Natural resource pulses influence social-network dynamics: experimental evidence from a tree cavity-dependent bird community

Natural resource pulses influence social-network dynamics: experimental evidence from a tree cavity-dependent bird community | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Natural resource pulses influence social-network dynamics: experimental evidence from a tree cavity-dependent bird community Andrea Rose Norris, Kathy Martin This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4360933/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract To explore how social networks might respond to ecological change we investigated the impact of two natural resource pulses at the foraging and nidic levels on intra- and inter-specific territorial behaviour of two species that co-occur year-round in multi-species groups. We simulated conspecific and heterospecific territorial intrusions in two insectivorous cavity-nesting species using 974 model presentations with territorial song playbacks during and after a dual resource pulse of insect (bark beetle) prey and nest cavities across 5 years in British Columbia, Canada. As beetle abundance increased, both species increased aggression toward conspecific intruders, but at peak beetle abundance, the (typically) subordinate generalist insectivore, mountain chickadee ( Poecile gambeli ), attacked model intruders more frequently than did the dominant bark insectivore, red-breasted nuthatch ( Sitta canadensis ). Surprisingly, chickadees shifted to an inter-specific resource defense strategy, responding more aggressively to nuthatch intruders than to conspecifics. Thus, obligate secondary cavity nesting chickadees dominated facultative excavating nuthatches, providing evidence of a dominance reversal at the nesting guild level. Both insectivores increased defense of high-quality territories, with increasing availability of food resources. The reversal in the interspecific dominance hierarchy suggests that behavioural mechanisms governing social networks and community structure may change during resource pulses. Overall, we suggest that social networks of chickadees and nuthatches are dynamic with high complexity and flexibility to major ecological disruptions. Future work that examines the fitness consequences of temporal variation in social network dynamics and resiliency could help to reveal evolutionary mechanisms by which these species co-exist. interspecific competition dominance hierarchies social resilience ecological resilience ecological disruption behavioural interactions Figures Figure 1 Figure 2 Figure 3 Significance Statement Links between social and ecological resilience may be important for animal societies, particularly as future generations experience rapid environmental change. Opportunities to evaluate how major environmental disruptions, such as resource pulses affect social networks in natural settings are extremely rare. By simulating territorial intrusions using song playbacks during and after a forest insect outbreak that resulted in a dual pulse of food and nest cavities for forest birds, we demonstrate that dominance hierarchies previously thought to govern year-round co-occurrence in chickadees and nuthatches can be reversed with increases in food resources for the typically dominant species (nuthatch). Our result that environmental variation allowed for plasticity in dominance hierarchies provides evidence that co-existence can be maintained through facilitative relationships (nuthatches providing nesting resources, and chickadees providing predator vigilance) between species that otherwise compete for food and nesting resources. Introduction Assessing the resiliency of social networks and predicting the responses of animal social systems to ecological change are emerging information needs in ecology (Shizuka and Johnson 2020 ; Strauss and Shizuka 2022 ; Coppinger et al. 2023 ). Many ecological and evolutionary processes are dependent on social networks that are affected by the biotic and abiotic contexts in which they occur (Thompson 1988 ; Chamberlain et al. 2014 ; Krams et al. 2020 ). Environmental change can destabilize existing social structures, leading to variable responses in social behaviour (Fisher et al. 2021 ). Resource pulses – brief, occasional, and intense events of high resource availability - may permeate through multiple levels of terrestrial and aquatic food webs to influence social networks (Ostfeld and Keesing 2000 ; Yang et al. 2008 ; St Clair et al. 2015 ). Examining thresholds of ecological change that lead to shifts in social network structure can help to reveal links between social and ecological resilience (Ilany and Akcay 2016 ). Studies of the effects of resource pulses on the variation in species interactions may help to fill key gaps in the functional dynamics of community ecology (Agrawal et al. 2007 ). In particular, there have been recent calls for more information on social networks and dominance hierarchies among multi-species groups (Coppinger et al. 2023 ). Variation in foraging niches within and among species has been shown to affect variation in social network structure (Feinsinger and Colwell 1978 ; López-Segoviano et al. 2018 ), a relationship demonstrated previously with experimentally pulsed resources (St Clair et al. 2015 ) but the opportunity to explore how natural resource pulses affect social interactions across species is rare. Forest bird communities are structured around complex social networks at the trophic and nidic levels, with species groups observed to be structured according to foraging and nesting guilds, respectively (Morse 1977 ; Martin et al. 2004 ; Sridhar et al. 2009 ; van der Hoek et al. 2020 ). In temperate regions, tits/chickadees (Paridae), nuthatches (Sittidae), and woodpeckers (Picidae) are among the bird species groups most frequently studied with respect to social networks due to their co-occurrence in both foraging and nesting guilds (Morse 1977 ; Martin et al. 2004 ). Chickadees show a great diversity of foraging behaviours as insect generalists, and while all species require tree cavities for nesting, some species are considered secondary cavity nesters as they do not typically excavate their cavities (Otter 2007 ; McCallum et al. 2020 ). Nuthatches are bark beetle-foraging specialists that are facultative excavators (I.e., they exhibit flexibility as they may excavate a new nesting cavity or use an existing cavity and are hereafter considered, excavators) (Matthysen 1998 ; Otter 2007 ). These differences in partitioning the foraging and nesting niches, (i.e., resource specialization) within the cavity-nesting community is hypothesized to allow for co-occurrence driving patterns in year-round coexistence (Martin et al. 2004 ; Chase and Leibold 2009 ). Species considered to be resource specialists are often stronger competitors due to their stronger reliance of some shared but limited resource (Chase and Leibold 2009 ); thus cavity limitation can drive competitive interactions among secondary cavity nesters (Aitken and Martin 2008 ) and bark beetle limitation could drive competitive interactions among bark beetle specialists. Community ecology lacks studies that experimentally test whether patterns in co-occurrence indicate ecological interactions driving community co-existence (Blanchet et al. 2020 ) but a dual resource pulse of both bark beetles and nesting cavities offers a unique opportunity to explore coexistence among species that vary in their specialization to each resource. Despite the niche differentiation nuthatches are found to be consistently dominant behaviourally over chickadees (Bock 1969 ; Otter 2007 ) with some exceptions reported (Waite and Grubb 1988 ). Both species exhibit aggressive behaviour towards conspecific and heterospecific individuals that threaten access to mates or food, which includes dominant individuals moving toward and supplanting their adversaries, and aggressive calls and displays that are unique to each species (Minock 1972 ; Waite and Grubb 1988 ). Socially, chickadees give alarm calls when predators are present, which nuthatches recognize and use to avoid predators (Templeton and Greene 2007 ; Carlson et al. 2020 ). In addition, chickadees use nesting cavities excavated by nuthatches, and their breeding populations show lagged positive functional and numerical responses to nuthatch densities (Aitken et al. 2002 ; Norris et al. 2013 , 2022 ). Due to their shared reliance on common resources and year-round co-occurrences including overlapping breeding territories and in rare instances nesting in the same tree cavity in the same year (Robinson et al. 2005 ), chickadees and nuthatches provide an excellent model in which to examine how a dual resource pulse in insect food and tree cavities affects their social network. Previously, we reported that chickadees used more cavities excavated by nuthatches, as nuthatches had excavated proportionately more new nest cavities in response to the food resource pulse of a forest insect (Mountain Pine Beetle, Dendroctonus ponderosae ), (Norris and Martin 2010 , 2014 ; Norris et al. 2013 , 2022 )). Here we used an experimental approach to infer the nature and strength of interactions within a population and between coexisting species (Martin et al. 1996 ; Martin and Martin 2001 ) to explore how changes in social network dynamics may have contributed to the observed plasticity in nesting behaviour that led to increased reproductive output for both species (Norris and Martin 2014 ; Norris et al. 2022 ). Specifically, we examine temporal variation in intra- and inter-specific interactions of mountain chickadee and red-breasted nuthatch, two small cavity-nesting competitors that show plasticity in their nest excavation behaviours and foraging strategies (on bark beetles). The identity of intruders often plays an important role in territoriality, particularly with respect to their relationship to the territory occupant such that neighbours and non-neighbours, or strangers, can elicit different responses depending on various factors such as environmental conditions and life history characteristics (Ydenberg et al. 1988 ; Eason and Hannon 1994 ; Müller and Manser 2007 ; Werba et al. 2022 ). For example, individuals that breed at lower densities and/or with sparse food resources can show higher aggression to territorial intrusions by novel intruders (strangers; dear enemy effect) relative to familiar intruders (neighbours), and individuals breeding at higher densities and/or with abundant food can show higher aggression to neighbours (nasty neighbour effect; (Yoon et al. 2012 )). We simulated territorial intrusions of conspecifics and heterospecifics to determine how the bark beetle outbreak and other environmental factors influenced the response of chickadees and nuthatches to territorial invaders. We evaluated our results with respect to three competing hypotheses suggested to influence species interactions (Fig. 1 ). Aggressive responses are predicted to: a) increase with increasing beetle abundance as the energy and potential reproductive benefits for individuals to defend high quality sites increases (Territory Investment Hypothesis), b) decrease towards heterospecifics but increase towards conspecifics, by expanding niche breadth, and reducing inter-specific dominance of resource specialists over generalists (Ecological Niche Hypothesis), or; c) decrease towards both species as individuals use the presence of conspecifics or heterospecifics with similar habitat requirements to assess territory quality (The Competitor Attraction Hypothesis). For example, if resource pulses impact these social networks according to the Territory Investment Hypothesis in which high quality resources are defended more aggressively, then intra- and inter-specific aggression among chickadees and nuthatches would both increase with higher beetle availability. The Ecological Niche Hypothesis (intra-specific mate competition is higher when inter-specific competition for the resources that most limit both species is low, (Chase and Leibold 2009 )) predicts that intra-specific aggression would increase with increasing beetle abundance, and inter-specific dominance of nuthatches over chickadees would be reduced. Alternatively, the Competitor Attraction Hypothesis in which tolerance of competitors increases as food resources are more abundant, predicts that both intra- and inter-specific aggression would decline with increasing beetle abundance (Fig. 1 ). Methods Study area We studied behaviour, fecundity, and habitat characteristics of cavity-nesting birds in 25 mixed coniferous-deciduous forest stands on the lands of the Tŝilhqot’in, Secwépemc, and Southern Dakelh Peoples, an area surrounding Williams Lake, British Columbia, Canada (51°52’N, 122°21’W), from 2004–2008. The predominant coniferous trees were Douglas-fir ( Pseudotsuga menziesii var. glauca ), lodgepole pine ( Pinus contorta var. latifolia ; hereafter, pine), and white and Engelmann hybrid spruce ( Picea glauca x engelmannii ; Meidinger and Pojar 1991). The predominant broadleaf tree was trembling aspen ( Populus tremuloides ). Study sites ranged from 15 to 32 ha (one 7-ha site) in size and varied in composition from continuous forest to five sites that comprised a series of ‘forest groves’ (0.2 to 5 ha) within a grassland matrix. Study system The small tree cavity nesting community comprised two species of insectivorous excavators and one secondary cavity nester (Martin and Eadie 1999 ). As many cavity excavators are also insectivores, large-scale insect outbreaks can lead to dual pulses in food and nest sites, potentially influencing the competitive interactions among tree cavity-dependent insectivores. Mountain pine beetle is a bark-boring insect that feeds on the phloem of pine trees and is a common disturbance agent in temperate forests that undergoes occasional patchy outbreaks in western North American forests (Taylor and Carroll 2003 ). Recent mountain pine beetle outbreaks in British Columbia increased year-round food availability, and subsequently, population densities of many insectivorous birds, including many excavators (Taylor and Carroll 2003 ; Martin et al. 2006 ). mountain chickadee ( Poecile gambeli ), a secondary cavity nester (cavity specialist) that relies on excavators and natural decay processes for nest cavities, is primarily a foliage gleaner, but can switch to other foraging substrates depending on forest insect abundance (McCallum et al. 2020 ). Red-breasted nuthatch ( Sitta canadensis ), is a facultative tree cavity nesting excavator, and is primarily a bark forager (Ghalambor and Martin 2020 ). The mountain pine beetle outbreak led to increases in population densities of both chickadees and nuthatches. Red-breasted nuthatch shifted nest site preference from areas of high nest site availability to those of high mountain pine beetle availability, where they excavated a greater proportion of nests (Norris and Martin 2008 , 2012 ). Mountain chickadee populations showed a one-year lag in increases following increased nuthatch populations, and used a greater proportion of smaller, safer nuthatch cavities following the beetle outbreak, suggesting that chickadee populations benefited from the higher densities of nuthatches (Norris et al. 2013 , 2022 ). However, the beetle outbreak also led to increased population densities of a common nest predator for chickadees and nuthatches, American red squirrel ( Tamiasciurus hudsonicus ;(Martin and Norris 2007 )). Because increased predator presence can lead to reduced parental activity around the nest resulting in reduced fecundity (Fontaine and Martin 2006 ), high squirrel densities may diminish territory quality and impede territory defence strategies. Such changes in territory characteristics could lead to increases or decreases in agonistic behaviour within and between species. We located nest trees of chickadees and nuthatches by checking all nesting cavities in trees used by other cavity-nesters in previous years (1995–2007) with a camera monitoring system on an extendable pole and by following individuals to their nests. We considered nests to be active if we found eggs or chicks in a cavity and monitored all nests until fledging or failure. Additional study area and nest monitoring details are given in (Martin and Eadie 1999 ; Aitken et al. 2002 ). Territorial intrusions We used song playbacks with intruder simulations to investigate interference competition within and between species (Martin et al. 1996 ) during territory establishment and before eggs were laid until after chicks fledged, between 1 May and 30 June, during (2004–2005) and after (2006–2008) the beetle outbreak (i.e., five years of measurement). To examine territorial responses of chickadees and nuthatches we simulated conspecific and heterospecific intrusions at six treatment types that represented two temporal- and two spatial-scales with respect to nesting (Table 1 ). We simulated intrusions within ~ 1 m of nest trees at nests that were active with either chickadees or nuthatches in the year of the presentation (1. active chickadee nest, 2. active nuthatch nest), 3. Nest cavities that were active in a previous year by either species (inactive nest), or within ~ 1 m of a tree suitable for excavation or nesting (aspen tree ≥ 15cm DBH, with or without existing tree cavities) but was not to our knowledge used for nesting by either species, and located in a random direction ~ 50m away from an active nest but still within the active territory (4. active chickadee territory, 5. active nuthatch territory) or 6. ~50m from an inactive nest within a territory not used by either chickadees or nuthatches in the year of the experiment (inactive territory). We compared responses of chickadees and nuthatches measured at each active, inactive, and suitable nest tree to those at suitable nest trees ~ 50 m from inactive nests (inactive territory) to assess the level of territorial aggression. The two species exhibit unique behaviours with respect to aggressive calls and displays, but both species exhibit the same behaviour of moving towards and supplanting intruders (Minock 1972 ; Grava et al. 2012 ). Therefore, we measured response to intruders by estimating the closest distance (m) that a respondent approached each intruder during each simulated intrusion to examine a common behaviour and compare interspecific responses (Kershner and Bollinger 1999 ). Although it was not possible to record data blind because our study involved focal animals in the field, we simulated intrusions of both species for each trial and presented each species in a random order. In 2004, we used song recordings from the second edition (1992) of the Peterson Field Guide audio compact disc from Cornell Lab of Ornithology, and during 2005–2008, we used recordings of songs of local chickadees and nuthatches collected ~ 20 km outside the study area. Songs were digitally manipulated so that each song was 2 min in length, and projected at similar volumes, then transferred onto a portable media player and broadcast over speakers. A taxidermic model specimen (intruder) of the appropriate species was placed on a wire stand ~ 1m above the speakers and presented with the appropriate song type for each trial, with a 5-min period of silence following each intruder species presented. For each respondent, we recorded the species, individual (if colour banded), sex, time of day, behaviour (whether the respondent: called and call type, sang, swooped, attacked, etc.), and the closest distance (m) that they approached to the model intruder. In cases where the respondent attacked the intruder, and aggression levels remained high, we waited 10 min to start the presentation of the next intruder species until the aggressive individual returned to displaying the behaviour observed before the first intruder was presented. In 2004, mountain chickadees approached conspecifics farther than in other years except 2007 (F 4,251 =5.17, p < 0.01), suggesting that the recordings of local chickadees elicited a stronger response from the Peterson’s recordings, so 2004 was excluded in analyses examining responses of mountain chickadees. Nuthatches approached conspecifics closer in 2004 relative to only 2008 (F 4,226 =5.34, p < 0.01), therefore 2004 was included in all nuthatch analyses. Where intrusions were simulated at active nest territories, we visually inspected the nest cavity using a pole-mounted video camera, and recorded fecundity characteristics (number of eggs or nestlings) and the stage of the nest to determine breeding status (pre-nest, egg-laying, incubating, chick-rearing). Table 1 We conducted 974 territorial intrusion experiments according to six plot types (distance to nest tree, species using the cavity, and active or inactive nest status) assigned by mean distance to nest tree (m) observed to be occupied by a chickadee or nuthatch breeding pair (Territory holder species) in the same year as the experiment or in a previous year (active/inactive nest status, respectively). To test the additional hypothesis that proximity to nest affects territoriality we conducted simulations ~ 50 m from active and inactive nests at (~ 1 m from) any available tree suitable for excavation or nesting (aspen tree ≥ 15cm DBH) but which was never, to our knowledge, used by either species. We broadcasted song recordings paired with presentations of taxidermically prepared specimens of mountain chickadee and red-breasted nuthatch procured from the Beaty Biodiversity Museum at the University of British Columbia, Vancouver, to simulate intrusions at 25 study sites in interior British Columbia, Canada, from 2004–2008. We compared the responses measured for each species at each active, inactive, and suitable nest tree to those at inactive territories. Plot type Distance (m) Territory holder species Nest status Active chickadee nest (ACN) 1 chickadee active Active nuthatch nest (ANN) 1 nuthatch active Inactive nest 1 chickadee and/or nuthatch inactive Active chickadee territory (ACT) 50 chickadee active Active nuthatch territory (ANT) 50 nuthatch active Inactive territory 50 neither inactive Population densities To determine how population densities of conspecifics and heterospecifics (including predators) influenced the behavioural responses, we conducted point count surveys to estimate population densities per ha of mountain chickadee, red-breasted nuthatch, and red squirrel at 25 sites, during 2004–2008. Point count stations were spaced within a 100 m square grid ≥ 50 m from a grassland or wetland edge (one station ha − 1 ) in continuous forest sites, and at least 100 m apart in forest groves. From 0500–0930 hours, we recorded the species, and number of individual birds and squirrels detected within 50-m radius 6-min point counts at each station (7–32 stations site − 1 ). Each station across the 25 sites was surveyed three times (rounds) in each of the 5 years. We divided the total number of individuals observed on all rounds by the total number of point counts to obtain estimates of mean individuals ha − 1 for each site and year. Further details of population monitoring methods were reported in earlier studies (Martin and Eadie 1999 ; Norris and Martin 2010 ). Vegetation surveys To determine whether spatial and temporal variation in food and nest site availability influenced species interactions, we established 0.04-ha circular vegetation plots centered at each point count station every year during 2004–2008. For all trees ≥12.5 cm diameter at breast height (DBH; measured at 1.3 m above ground) in each plot, we recorded tree species, DBH, general health (e.g., presence of boring insects on the bole), and decay class. Decay class 1 was a live, healthy tree, 2 a live tree with visible sign of bark boring insects or heart rot fungus, and 3–8 were standing dead trees in progressive states of decay (Thomas 1979 ). Before and during the study period, an outbreak of mountain pine beetle occurred across all sites, with incidence of beetle attacks on pines increasing sharply after 2002, and by 2005 over 95% of the mature lodgepole pine trees (40% of the trees on the sites) were dead (Edworthy et al. 2011 ). However, the onset of the beetle outbreak showed temporal and spatial variation in the number of trees showing sign of beetle attack (Drever et al. 2009 ). Therefore, we could examine the effects of beetle abundance at the site-year level. Beetle eggs are laid beneath the bark in late summer where they overwinter and beetle larvae complete development in the following summer before emerging as adults (Reid 1962 ). Thus, beetle larvae provided a rich food source throughout the winters and following breeding seasons for insectivores. We determined beetle-infected pine densities as the total number of decay class 2 pine trees with bark boring insects, which was evident by the presence of dried resin outflows, or small entry holes (~ 2mm in diameter) on the bark, expressed on a per ha basis divided by the total number of 0.04 ha vegetation plots, for each site and year. Since over 90% of chickadee and nuthatch nests were in aspen trees (Martin and Eadie 1999 ), we determined the densities of potential nest trees per ha from number of aspen trees divided by the total number of 0.04 ha plots, for each site and year. Statistical analyses We examined how territory characteristics (proximity to active and inactive nests, food and nest site availability, and population densities of conspecifics, and heterospecifics, including squirrels) influenced intra- and inter-specific aggression of chickadees and nuthatches. We used the closest distance (m) that a respondent approached each intruder during the territory intrusion simulation as the metric of aggression. For both species, the data for closest distance approached were heavily skewed toward zero and showed an uneven distribution in the number of response variables between 0–50 m. As a result of the truncated normal distribution and the high number of zero values, we applied a mixture of the binomial (for closest distance = 0 or > 0) and left-truncated normal (for closest distance > 0) distributions. We used linear mixed-effects models (Crawley 2012 ) to examine how variation in closest distance approached was explained by the fixed-effects variables: intruder species (conspecific or heterospecific), plot type of the experiment (active chickadee nest; ACN, active nuthatch nest; ANN, inactive nest, active chickadee territory; ACT, active nuthatch territory; ANT, or inactive territory), breeding status of territory owners (if on an active nest plot), presentation sequence of intruders, and abundance of food (beetle-infected live pine densities per ha for the corresponding site and year in which the intrusion experiment was conducted) and nest sites (nest-tree densities per ha), and densities per ha of red-breasted nuthatch, mountain chickadee, and red squirrel, and all biologically relevant secondary interaction terms. Because we conducted intrusion experiments at multiple locations (plots) within sites and at multiple sites within years, we included plot nested within site as a random effect to account for the hierarchical error structure due to the repeated measures, in all models. Since the repeated measures were not evenly spaced within and between plots, we added a continuous autoregressive correlation within plots. These hierarchical errors were assumed to have normal distributions. We used penalized quasi-likelihood (PQL) methods to generate parameter estimates (Bolker et al. 2009 ). We used Wald’s t-test to eliminate fixed-effects variables from fully parameterized models, and to determine whether fixed-effect variables had a significant effect on the response variables given the other fixed-effect variables and the hierarchical error structure in the best-fit (final) model (Bolker et al. 2009 ). Negative signs of significant coefficients indicated that the closest distance approached decreased (I.e., the responding bird approached closer to the model, and was more aggressive) and positive signs indicated that distance approached increased (the bird approached further distances, and was less aggressive) with increases in the fixed effect variables (Crawley 2012 )). Penalized quasi-likelihood estimates were obtained using the function glmmPQL in the library MASS, and all data analyses were conducted in the program R version 2023.06.1 (R Core Team 2013; Ripley et al. 2013 ). Results We simulated 974 territorial intrusions across 25 sites, during 2004–2008. We detected 397 responses (i.e., at least one adult detected < 50 m from intruder) from the bark beetle generalist, mountain chickadee, and 372 responses from red-breasted nuthatch (bark beetle specialist). In 95 cases (23.9%) for mountain chickadees and in 30 cases (8.1%) for red-breasted nuthatch, respondents struck the intruder, knocking it to the ground, and then repeatedly attacked the intruder until the observer removed it. Overall, both species approached intruders closer when simulations were conducted on active nest plots (~ 1m from nest tree; ACN, ANN) compared to inactive territories and nuthatches also approached closer at suitable nest trees located ~ 50m away from active nests (active nuthatch territories; ANT) than those in inactive territories. Both species showed similar responses to conspecific intruders (mean closest distance approached: mountain chickadee, 9.1 m ± 0.77 SE; Nuthatch, 11 m ± 0.80 SE), but mountain chickadees approached heterospecific intruders significantly closer than did nuthatches (14 m ± 1.1 SE, and 21m ± 1.2 SE, respectively; Fig. 2 ). During the beetle outbreak (2004–2006), both species approached closer than the overall mean, and approached heterospecifics at least as close as the overall mean approach to conspecifics. After the beetle outbreak (2007–2008) neither species approached the intruder as close as those respondents measured during the beetle outbreak. Table 2 Mountain chickadee responses to conspecific and nuthatch territorial intruders across 112 plots at 25 sites in interior British Columbia, from 2005–2008. Parameter estimates (Estimate), standard errors (SE), and degrees of freedom (DF) of the final mixture distribution (normal and binomial), linear mixed-effects model, generated using penalized quasi-likelihood of closest distance approached by mountain chickadees to simulated intruders of red-breasted nuthatch (NM) and mountain chickadee (CM) at various locations (plots) within territories compared to inactive territories, with spatial and temporal variation in beetle abundance (beetle-infected pine densities; Be), and nuthatch densities. Estimates were generated from the final model, Closest distance ~ Intruder + Beetle density (Be) + Chickadee density + Nuthatch density + Plot type (PT) + Be PT; random effects = Site / Plot ID, with continuous autoregressive correlation within Plot ID. Fixed effect variables had significant effects on distance approached to intruders where p < 0.1, in bold. Although the responses in five classes of plot type were compared to those in random plots in inactive territories, only classes with significant effects are listed. Fixed Effect Estimate SE DF t-value p-value Model Intercept 15 2.6 211 5.9 < 0.001 Nuthatch model (NM; relative to CM) 6.4 1.5 211 4.2 < 0.002 Beetle-infected pine density (Be) 130 70 211 1.8 0.076 Chickadee density -8.7 4.8 211 -1.8 0.073 Nuthatch density 25 12 211 2.1 0.041 PT: Active chickadee nest (ACN) -9 2.3 211 -3.8 0.0002 Be x ACN interaction -140 70 211 -2 0.052 Table 3 Red-breasted nuthatch responses to conspecific and chickadee territorial intruders across 114 plots at 25 sites in interior British Columbia, from 2004–2008. Parameter estimates (Estimate), standard errors (SE), and degrees of freedom (DF) of the final mixture distribution (normal and binomial), linear mixed-effects model generated using penalized quasi-likelihood for closest distance approached by red-breasted nuthatches to simulated intruders of red-breasted nuthatch (NM) and mountain chickadee (CM), at various locations (plots) within active territories compared to inactive territories with spatial and temporal variation in beetle abundance (beetle-infected pine densities; Be), and Nuthatch densities. Estimates were generated from the final model, Closest distance ~ Intruder + Beetle (Be) + Nuthatch density + Plot type (PT) + Be PT; random effects = Site/Plot ID, with continuous autoregressive correlation within Plot ID. Fixed-effect variables with significant effects on distance approached to intruders where p < 0.1, given in bold. Although responses in five classes of plot type were compared to those in inactive territories, only classes with significant effects are listed. Fixed Effect Estimate SE DF t-value p-value (Intercept) 24 2.4 157 10 < 0.001 Nuthatch model (relative to CM) -12 1.5 157 -8.4 < 0.001 Beetle-infected pine density (Be) 16 18 157 0.89 0.37 Nuthatch density 22 9.3 157 2.3 0.021 PT: Active nuthatch territory (ANT) -4.7 3.1 157 -1.5 0.13 PT: Active nuthatch nest (ANN) -12 2.4 157 -4.9 < 0.001 Be x ANT interaction -44 26 157 -1.7 0.098 Be x ANN interaction -37 21 157 -1.8 0.08 Mountain chickadee On average, chickadees approached all intruders closest at experiments conducted in the immediate proximity of (~ 1 m from) active chickadee nests (Table 2 ) and conspecific intruders closer than heterospecific intruders, ( β NM = 6.4 ± 1.5 SE), which supported the Ecological Niche Hypothesis. However, as beetle abundance increased (2005 and 2006), chickadees approached heterospecific intruders closer than conspecific intruders at active chickadee nests ( β BexACN = -140 ± 70 SE; Fig. 3 ), supporting the Territory Investment Hypothesis (Table 2 ). Chickadees showed a nasty neighbour effect towards conspecifics, approaching intruders closer with increasing chickadee densities, but a dear enemy effect towards nuthatches, approaching farther with increasing nuthatch densities. Red-breasted nuthatch Consistent with the Ecological Niche Hypothesis, the final model describing variation in the closest distance approached to intruders predicted that nuthatches approached conspecifics closer than to chickadees ( β NM = -12 1.5 SE; Table 3 ). Nuthatches showed a dear enemy effect towards conspecifics, approaching intruders farther with increasing nuthatch densities. The relationship between response distance and beetle abundance depended upon whether the nest plot was active or inactive: Consistent with the Territory Investment Hypothesis, nuthatches approached intruders closer with increasing beetle abundance in active nuthatch territories (both at active nests and suitable nest trees ~ 50m from the nest; β BexANN = -37 21 SE, β BexANT = -44 26 SE, respectively), compared to suitable nest trees in inactive territories that were unoccupied by both chickadees and nuthatches in the year of the experiment. Discussion We found support for both the Ecological Niche and Territory Investment Hypotheses at different spatial and temporal scales. Chickadees showed greater annual variability in their responses and were more aggressive than nuthatches across all territories, sites, and years, consistent with the Ecological Niche Hypothesis. Nuthatches approached conspecific intruders twice as close as heterospecific intruders, overall, and approached intruders closest at both active nests and at suitable nest trees near active nuthatch nests (active nuthatch territories) relative to inactive territories. Both species were more aggressive to nuthatch intruders at active nest territories at sites and in years with increasing beetle abundance, suggesting that: 1) the more efficient beetle-foragers (nuthatches) may pose a greater threat to territory intrusion during beetle outbreaks, and 2) individuals increased their investment in territory defence with increases in food availability (Territory Investment Hypothesis). As with any experimental study design, our results are limited to those variables examined. Social networks are likely influenced by other factors affecting communication in animals such as demographic features, visual, auditory and other sensory cues such as vibrational signals (Hill 2001 ; Erbe and Thomas 2022 ), and the presence of other species including humans (Coppinger et al. 2023 ). Our experimental approach of presenting a model and broadcasting auditory signals, although a standard approach to measuring behavioural responses might have influenced the ways in which these species normally interact with one another within this spatial and temporal context. Ecological niche hypothesis In earlier work, we found that shifts in habitat and cavity preferences led to increases in reproductive output for both species, and hypothesized that increases in food availability could reduce territorial disputes (Norris et al. 2013 , 2022 ; Norris and Martin 2014 ). Our finding that responses to heterospecifics were stronger in chickadees than nuthatches (24% of responses by mountain chickadees led to an attack vs. 8% by nuthatches) is similar to another study approximately 300 km north of our study area, where mountain chickadees showed similar responses to conspecific intruders and to the behaviourally dominant heterospecific intruder, Black-capped chickadee ( Poecile atricapillus ), a small cavity excavator (Grava et al. 2012 ). Despite previous observations and generally accepted knowledge among titmice experts that nuthatches are behaviourally dominant over chickadees (Bock 1969 ; Kershner and Bollinger 1999 ; Otter 2007 ), others occasionally have found chickadees or titmice to be socially dominant over nuthatches in foraging flocks (Waite and Grubb 1988 ). Dhondt (Dhondt 1989 , 2012 ) has even suggested that greater interspecific (relative to intraspecific) competition during the breeding season is an evolutionary balancing mechanism promoting year-round coexistence in tits. As with the Dhondt studies, chickadees in our study showed unexpectedly higher aggression to their dominant heterospecific competitor during the breeding season. Notably, most studies of dominance hierarchies in titmice are conducted outside the breeding season and where patterns in social dominance are inferred from mainly from access to food (Waite and Grubb 1988 ; Ghalambor and Martin 2020 ; McCallum et al. 2020 ), rather than breeding resource supply. At the nesting guild, nest cavity resource specialists, or those who have greater limitation to nest-sites can behaviourally dominate generalists (in this case, we refer to those species capable of excavating their own cavity; Aitken and Martin 2008 ). For example, the secondary cavity nester, European starling ( Sturnus vulgaris ), can usurp cavities from excavating woodpeckers who also reuse cavities by initiating their nests before woodpeckers (Wiebe 2003 ; Frei et al. 2015 ). Thus, Starlings are often considered a behaviourally dominant species in the nest web, often having negative impacts on breeding success of rivals through interference competition (Wiebe 2003 ; Aitken and Martin 2008 ; Frei et al. 2015 ). Mountain chickadees initiated nests ~ 15d earlier than nuthatches, suggesting that earlier nesting facilitated their dominance over nuthatches (Norris and Martin 2014 ; Norris et al. 2022 ). In the first year of our study we reported an instance of nest sharing between mountain chickadee and red-breasted nuthatch, with a female nuthatch displacing a chickadee pair during the nestling stage and successfully fledging both nuthatch and chickadee young from the nest (Robinson et al. 2005 ) suggesting that chickadees have reproductive incentive to defend their nests against the more dominant heterospecific to prevent nest usurpation. Thus, our findings support the Ecological Niche Hypothesis and suggest that the dominance hierarchy between chickadees and nuthatches varies and can be reversed on breeding territories during resource pulses. These two species groups are the only cavity-nesting passerines to remain in boreal and hemi-boreal temperate regions during winter and due to their year-round co-occurrence and niche overlap probably have highly complex social networks and many other important social dynamics not tested here. Model systems where rank can be manipulated are suggested to be extremely useful for testing hypotheses about dominance network dynamics (Strauss and Shizuka 2022 ). We suggest that future work should explore the generality of our findings that chickadees that are subordinate in foraging groups can become dominant to excavating nuthatches on breeding territories during resource fluctuations. Competitor attraction hypothesis Since both species approached nuthatch intruders closest at active nest territories, it is possible that both species used nuthatches as cues in territory establishment and the distance approached to nuthatch intruders represented territory prospecting rather than defence. However, we found a significantly negative correlation between the elicited behaviour of attacking the model and distance approached to the model (In the simple linear model, Closest distance ~ Attacker vs. non-attacker, for chickadees, A = -13 m 1.8 SE, t = -6.8, p < 0.01, and nuthatches, A = -16 m 3.3 SE, t = -4.7, p < 0.01) suggesting that the closest distance approached indeed represented an aggressive response rather than a passive, exploratory response. Further, if individuals were using the presence of nuthatches to assess new territories, we would expect a closer approach to nuthatch intruders at all territories. Yet, both species approached similar distances to both nuthatch and chickadee intruders at heterospecific territories ( p > 0.1; Interaction effect of heterospecific nest plot and nuthatch intruder for both species), and the increased responses to nuthatch intruders were only observed at conspecific territories (Tables 1 , 2 ), indicating territorial defence responses. Since distance approached was correlated with an aggressive response, and both species approached intruders closer with increasing beetle abundance, neither intra- nor inter-specific aggression was reduced with increases in food availability, as was predicted under the competitor attraction hypothesis. Thus, we were able to reject both the conspecific and heterospecific attraction hypotheses for both chickadees and nuthatches. Territory investment hypothesis Both species showed an increasingly aggressive response to all intruders at active nest trees and nearby suitable nest trees within territories, with increasing beetle abundance, suggesting that investment in territorial defence increased with the beetle outbreak (or more accurately, investment declined with reductions in beetle availability at the temporal scale measured in this study). Food-supplemented song sparrows ( Melospiza melodia ) in the northeastern United States were more aggressive to territorial intruders than non-supplemented birds, particularly in rural environments where birds were less aggressive overall and resources were potentially more limited relative to those in urban areas (Foltz et al. 2015 ). High levels of aggression and territorial defence often require elevated energy expenditures, but territories containing ample resources required for increased defence may also provide greater reproductive benefits as the energy spent on territorial defence is readily recouped (Martin 1987). In cavity-nesting Prothonotary Warblers ( Protonotaria citrea ), pairs occupying higher quality territories produced more fledglings and competitively excluded other pairs from territories (Petit and Petit 1996 ). Mountain pine beetles provide a year-round food source from late summer when adult beetles lay eggs beneath the bark to the following summer when larval development is completed (Reid 1962 ). As both chickadees and nuthatches are winter residents, the beetle outbreak likely increased the energy reserves of individuals over winter and in spring before the breeding season. During the beetle outbreak, chickadees laid earlier and larger clutches, and had a higher probability of fledging nestlings, and nuthatches laid larger clutches later in the breeding season compared to before the outbreak (Norris and Martin 2014 ; Norris et al. 2022 ). Thus, it is likely that territories with high beetle abundance provided more food resulting in earlier nesting and higher fecundity, leading to an increase in territoriality before and during territory establishment in both species. Our result that chickadees approached intruders closer at sites and in years with increasing chickadee densities, supported the nasty neighbour effect that neighbouring conspecifics pose a greater threat than strangers due to higher potential for competition over resources and access to mates leading to positive density-dependent aggression (Brown 1964 ; Yoon et al. 2012 ). Contrary to their response to conspecific densities, however, chickadees showed lower aggression with rising nuthatch densities. Nuthatches also showed lower aggression with rising nuthatch densities, and both species were most aggressive to nuthatch intruders in the years of lowest nuthatch population densities (2005–2006; Fig. 2 ; (Norris and Martin 2010 )). Breeding populations of both chickadees and nuthatches showed high annual variability, and the result that aggression toward nuthatch intruders was higher when nuthatch densities were lowest and lower when densities were highest suggest that unfamiliar nuthatches (strangers) may pose a greater threat than neighbouring nuthatches, providing support for the ‘dear enemy’ effect that both species were less aggressive towards familiar nuthatches (i.e., a known threat), and avoided the costs associated with repetitive territorial disputes. The result that chickadees could switch between the nasty neighbour effect to conspecifics and the dear enemy effect to nuthatches indicates behavioural plasticity in territoriality, a pattern shown to occur across the breeding season for dusky warblers ( Phylloscopus fuscatus ) in Hebei, China (Wang et al. 2022 ). We provided evidence to support both the nasty neighbour and dear enemy effects in chickadees and nuthatches and suggest that future work examine how plasticity in territoriality across the year may contribute to the complex social networks and co-existence in this species group. Conclusion We found that a cavity specialist and foraging generalist chickadee dominated nuthatch (a beetle specialist and cavity generalist), suggesting that inter-specific dominance hierarchies observed at foraging guilds can be reversed in the breeding season during resource pulses. Increases in intra- and inter-specific competition with increases in beetle abundance suggests that behavioural mechanisms governing community structure may change dramatically during resource pulses that increase the disparity in territory quality. Our observation that aggressive responses declined following the beetle outbreak, returning to the typically reported relationships among chickadees and nuthatches suggests that these social networks exhibit resiliency following resource pulses. Future work that further examines the variation in responses to conspecifics and heterospecifics and their associated fitness consequences within the context of resource limitation might reveal how social networks may regulate year-round coexistence among these species groups (Dhondt 2012 ; Coppinger et al. 2023 ). Declarations Data availability All data generated or analyzed during this study are included in this published article (and its supplementary information files). Supplementary Information Below is the link to the electronic supplementary material. Supplementary file1 (Playbackdata_submit.csv) Supplementary file2 (Playbacks_submit.R) Ethics declarations Potential conflicts of interest We declare that we have no financial or non-financial competing interests to disclose. Research involving animal participants We followed all protocols required by the Animal Care Committees of the University of British Columbia and Environment and Climate Change Canada, under annually renewed permits from the University of British Columbia Animal Care Protocol and Environment and Climate Change Canada’s scientific permit and banding permit number 10365. Informed consent Both authors gave final approval for publication and agreed to be held accountable for the work performed therein. Acknowledgements We are grateful for Tŝilhqot’in, Secwépemc, and Southern Dakelh Peoples for their historical and continued relationships with these lands and the other-than human relatives, with whom these studies were conducted. We are grateful for the chickadee and nuthatch relatives who were involved in this study. We thank the many field technicians who assisted in data collection, specifically D. Gunawardana, M. Marjanovic, I. Behret, M. Behret, H. Kenyon, M. Edworthy, and K. Scotton. D. Cockle built and maintained the cavity monitoring equipment. Scout Island Nature Society in Williams Lake, BC donated the specimens for the models used in territorial intrusions. Discussions with K. Aitken, K. Wiebe, and D. Shizuka helped to shape the behavioural field trials, and A. Boyle, D. Weary, and discussions with the Martin-Arcese Lab group improved the quality of the manuscript. V. LeMay, D. Irwin, J. McLean, and J. Goheen assisted in study design. Statements and Declarations Funding: Research grants were awarded to KM from the Natural Sciences and Engineering Research Council of Canada (NSERC), Environment and Climate Change Canada, and Tolko Limited. ARN received post-graduate scholarships from NSERC, a Four-Year Doctoral Fellowship and a Pacific Century Graduate Scholarship from the University of British Columbia, and research grants from the Forest Investment Account Forest Science Program (Graduate Student Pilot Project and Mountain Pine Beetle Initiative Graduate Research Fund), the Southern Interior Bluebird Trail Society, and a Junco Technologies Award from the Society of Canadian Ornithologists and Bird Studies Canada. References Agrawal AA, Ackerly DD, Adler F et al (2007) Filling key gaps in population and community ecology. Front Ecol Environ 5:145–152 Aitken KEH, Martin K (2008) Resource selection plasticity and community responses to experimental reduction of a critical resource. Ecology 89:971–980. https://doi.org/10.1890/07-0711.1 Aitken KEH, Wiebe KL, Martin K (2002) Nest-Site Reuse Patterns for a Cavity-Nesting Bird Community in Interior British Columbia. Auk 119:391–402. https://doi.org/10.1093/auk/119.2.391 Blanchet FG, Cazelles K, Gravel D (2020) Co-occurrence is not evidence of ecological interactions. Ecol Lett 23:1050–1063. https://doi.org/10.1111/ele.13525 Bock CE (1969) Intra- vs. Interspecific Aggression in Pygmy Nuthatch Flocks. Ecology 50:903–905. https://doi.org/10.2307/1933706 Bolker BM, Brooks ME, Clark CJ et al (2009) Generalized linear mixed models: a practical guide for ecology and evolution. Trends Ecol Evol 24:127–135 Brown JL (1964) The evolution of diversity in avian territorial systems. Wilson Bull 160–169 Carlson NV, Greene E, Templeton CN (2020) Nuthatches vary their alarm calls based upon the source of the eavesdropped signals. Nat Commun 11:526. https://doi.org/10.1038/s41467-020-14414-w Chamberlain SA, Bronstein JL, Rudgers JA (2014) How context dependent are species interactions? Ecol Lett 17:881–890. https://doi.org/10.1111/ele.12279 Chase JM (2011) Ecological niche theory. Theory Ecol 93–107 Chase JM, Leibold MA (2009) Ecological niches: linking classical and contemporary approaches. University of Chicago Press Coppinger BA, Carlson NV, Freeberg TM, Sieving KE (2023) Mixed-species groups and the question of dominance in the social ecosystem. Philos Trans R Soc B Biol Sci 378:20220097. https://doi.org/10.1098/rstb.2022.0097 Crawley MJ (2012) The R book. Wiley Dhondt AA (1989) Ecological and Evolutionary Effects of Interspecific Competition in Tits. Wilson Bull 101:198–216 Dhondt AA (2012) Interspecific competition in birds. Oxford Avian Biology Drever MC, Goheen JR, Martin K (2009) Species–energy theory, pulsed resources, and regulation of avian richness during a mountain pine beetle outbreak. Ecology 90:1095–1105 Eason P, Hannon S (1994) New birds on the block: new neighbors increase defensive costs for territorial male willow ptarmigan. Behav Ecol Sociobiol 34:419–426 Edworthy AB, Drever MC, Martin K (2011) Woodpeckers increase in abundance but maintain fecundity in response to an outbreak of mountain pine bark beetles. Ecol Manag 261:203–210 Erbe C, Thomas JA (2022) Exploring Animal Behavior Through Sound: Volume 1: Methods. Springer Nature Feinsinger P, Colwell RK (1978) Community Organization Among Neotropical Nectar-Feeding Birds. Am Zool 18:779–795. https://doi.org/10.1093/icb/18.4.779 Fisher DN, Kilgour RJ, Siracusa ER et al (2021) Anticipated effects of abiotic environmental change on intraspecific social interactions. Biol Rev 96:2661–2693. https://doi.org/10.1111/brv.12772 Foltz SL, Ross AE, Laing BT et al (2015) Get off my lawn: increased aggression in urban song sparrows is related to resource availability. Behav Ecol 26:1548–1557. https://doi.org/10.1093/beheco/arv111 Fontaine JJ, Martin TE (2006) Habitat selection responses of parents to offspring predation risk: an experimental test. Am Nat 168:811–818 Frei B, Nocera JJ, Fyles JW (2015) Interspecific competition and nest survival of the threatened Red-headed Woodpecker. J Ornithol 156:743–753 Ghalambor CK, Martin TE (2020) Red-breasted Nuthatch (Sitta canadensis). In: Billerman SM, Keeney BK, Rodewald PG, Schulenberg TS (eds) Birds of the World. Cornell Lab of Ornithology Grava A, Grava T, Otter KA (2012) Differential Response to Interspecific and Intraspecific Signals Amongst Chickadees. Ethology 118:711–720. https://doi.org/10.1111/j.1439-0310.2012.02061.x Hill PS (2001) Vibration and animal communication: a review. Am Zool 41:1135–1142 Ilany A, Akcay E (2016) Social inheritance can explain the structure of animal social networks. Nat Commun 7:12084 Kershner EL, Bollinger EK (1999) Aggressive Response of Chickadees Towards Black-Capped and Carolina Chickadee Calls in Central Illinois. Wilson Bull 111:363–367 Krams IA, Luoto S, Krama T et al (2020) Egalitarian mixed-species bird groups enhance winter survival of subordinate group members but only in high-quality forests. Sci Rep 10:4005. https://doi.org/10.1038/s41598-020-60144-w López-Segoviano G, Bribiesca R, Arizmendi MDC (2018) The role of size and dominance in the feeding behaviour of coexisting hummingbirds. Ibis 160:283–292. https://doi.org/10.1111/ibi.12543 Martin K, Aitken KEH, Wiebe KL (2004) Nest Sites and Nest Webs for Cavity-Nesting Communities in Interior British Columbia, Canada: Nest Characteristics and Niche Partitioning. Condor 106:5–19 Martin K, Eadie JM (1999) Nest webs: A community-wide approach to the management and conservation of cavity-nesting forest birds. Ecol Manag 115:243–257. https://doi.org/10.1016/S0378-1127(98)00403-4 Martin K, Norris A (2007) Life in the small-bodied cavitynester guild: Demography of sympatric mountain and black-capped chickadees within nest web communities under changing habitat conditions. Ecol Behav Chickadees Titmice Integr Approach 111–130 Martin K, Norris A, Drever M (2006) Effects of bark beetle outbreaks on avian biodiversity in the British Columbia interior: Implications for critical habitat management. J Ecosyst Manag Martin PR, Fotheringham JR, Ratcliffe L, Robertson RJ (1996) Response of American redstarts (suborder Passeri) and least flycatchers (suborder Tyranni) to heterospecific playback: the role of song in aggressive interactions and interference competition. Behav Ecol Sociobiol 39:227–235 Martin PR, Martin TE (2001) Behavioral interactions between coexisting species: song playback experiments with wood warblers. Ecology 82:207–218 Matthysen E (1998) The nuthatches. A&C Black McCallum DA, Grundel R, Dahlsten DL (2020) Mountain Chickadee (Poecile gambeli). In: Billerman SM, Keeney BK, Rodewald PG, Schulenberg TS (eds) Birds of the World. Cornell Lab of Ornithology Minock ME (1972) Interspecific aggression between black-capped and mountain chickadees at winter feeding stations. Condor 74:454–461 Mönkkönen M, Helle P, Soppela K (1990) Numerical and behavioural responses of migrant passerines to experimental manipulation of resident tits (Parus spp.): heterospecific attraction in northern breeding bird communites? Oecologia 85:218–225 Morse DH (1977) Feeding Behavior and Predator Avoidance in Heterospecific Groups. Bioscience 27:332–339. https://doi.org/10.2307/1297632 Morse DH (1974) Niche breadth as a function of social dominance. Am Nat 108:818–830 Müller CA, Manser MB (2007) Nasty neighbours’ rather than ‘dear enemies’ in a social carnivore. Proc R Soc B Biol Sci 274:959–965 Norris AR, Drever MC, Martin K (2013) Insect outbreaks increase populations and facilitate reproduction in a cavity-dependent songbird, the M ountain C hickadee P oecile gambeli. Ibis 155:165–176 Norris AR, Martin K (2010) The perils of plasticity: dual resource pulses increase facilitation but destabilize populations of small-bodied cavity-nesters. Oikos 119:1126–1135 Norris AR, Martin K (2014) Direct and indirect effects of an insect outbreak increase the reproductive output for an avian insectivore and nest-cavity excavator, the red-breasted nuthatch Sitta canadensis. J Avian Biol 45:280–290 Norris AR, Martin K (2008) Mountain pine beetle presence affects nest patch choice of red-breasted nuthatches. J Wildl Manag 72:733–737 Norris AR, Martin K (2012) Red-breasted nuthatches (Sitta canadensis) increase cavity excavation in response to a mountain pine beetle (Dendroctonus ponderosae) outbreak. Ecoscience 19:308–315 Norris AR, Martin K, Cockle KL (2022) Weather and nest cavity characteristics influence fecundity in mountain chickadees. PeerJ 10:e14327 Ostfeld RS, Keesing F (2000) Pulsed resources and community dynamics of consumers in terrestrial ecosystems. Trends Ecol Evol 15:232–237 Otter KA (2007) Ecology and Behavior of Chickadees and Titmice: An Integrated Approach. OUP Oxford Petit LJ, Petit DR (1996) Factors governing habitat selection by prothonotary warblers: field tests of the Fretwell-Lucas models. Ecol Monogr 66:367–387 R Core Team R (2013) R: A language and environment for statistical computing Reid R (1962) Biology of the Mountain Pine Beetle, Dendroctonus monticolae Hopkins, in the East Kootenay Region of British Columbia I. Life Cycle, Brood Development, and Flight Periods1. Can Entomol 94:531–538 Ripley B, Venables B, Bates DM et al (2013) Package ‘mass’. Cran R 538:113–120 Robinson PA, Norris AR, Martin K (2005) Interspecific nest sharing by Red-breasted Nuthatch and Mountain Chickadee. Wilson Bull 117:400–402 Shizuka D, Johnson AE (2020) How demographic processes shape animal social networks. Behav Ecol 31:1–11. https://doi.org/10.1093/beheco/arz083 Sridhar H, Beauchamp G, Shanker K (2009) Why do birds participate in mixed-species foraging flocks? A large-scale synthesis. Anim Behav 78:337–347. https://doi.org/10.1016/j.anbehav.2009.05.008 St Clair JJH, Burns ZT, Bettaney EM et al (2015) Experimental resource pulses influence social-network dynamics and the potential for information flow in tool-using crows. Nat Commun 6:7197. https://doi.org/10.1038/ncomms8197 Stamps JA (1988) Conspecific attraction and aggregation in territorial species. Am Nat 131:329–347 Strauss ED, Shizuka D (2022) The dynamics of dominance: open questions, challenges and solutions. Philos Trans R Soc B Biol Sci 377:20200445. https://doi.org/10.1098/rstb.2020.0445 Taylor SW, Carroll AL (2003) Disturbance, forest age, and mountain pine beetle outbreak dynamics in BC: A historical perspective. Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre … Templeton CN, Greene E (2007) Nuthatches eavesdrop on variations in heterospecific chickadee mobbing alarm calls. Proc Natl Acad Sci 104:5479–5482 Thomas JW (1979) Wildlife habitats in managed forests: the Blue Mountains of Oregon and Washington. Wildlife Management Institute Thompson JN (1988) Variation in Interspecific Interactions. Annu Rev Ecol Syst 19:65–87. https://doi.org/10.1146/annurev.es.19.110188.000433 van der Hoek Y, Gaona GV, Ciach M, Martin K (2020) Global relationships between tree-cavity excavators and forest bird richness. R Soc Open Sci 7:192177 Waite TA, Grubb TC (1988) Copying of Foraging Locations in Mixed-Species Flocks of Temperate-Deciduous Woodland Birds: An Experimental Study. Condor 90:132–140. https://doi.org/10.2307/1368442 Wang H, Ma L, Wang J, Hou J (2022) Modulation of dear enemy effects by male dusky warblers (Phylloscopus fuscatus) at different reproductive stages. Behav Processes 200:104706. https://doi.org/10.1016/j.beproc.2022.104706 Werba JA, Stuckert AM, Edwards M, McCoy MW (2022) Stranger danger: A meta-analysis of the dear enemy hypothesis. Behav Processes 194:104542. https://doi.org/10.1016/j.beproc.2021.104542 Wiebe KL (2003) Delayed timing as a strategy to avoid nest-site competition: testing a model using data from starlings and flickers. Oikos 100:291–298 Yang LH, Bastow JL, Spence KO, Wright AN (2008) What can we learn from resource pulses. Ecology 89:621–634 Ydenberg RC, Giraldeau L, Falls JB (1988) Neighbours, strangers, and the asymmetric war of attrition. Anim Behav 36:343–347 Yoon J, Sillett TS, Morrison SA, Ghalambor CK (2012) Breeding density, not life history, predicts interpopulation differences in territorial aggression in a passerine bird. Anim Behav 84:515–521. https://doi.org/10.1016/j.anbehav.2012.05.024 Supplementary Files Playbackdatasubmit.csv Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4360933","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":303567157,"identity":"461c819a-3c63-4d88-bca5-fb7dc516d437","order_by":0,"name":"Andrea Rose Norris","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABB0lEQVRIiWNgGAWjYHACAzjrAEMFgwyEAULEaTnDwEOaFgbGNogWBnxa+Gc3b/vwoYYhj1/67MODP+fZ8RhcO3vwAGPbHXkG9sMPsGmRuHOseOaMYwzFkn3pBod5tyXzGNzOSwBqeWbYwJNmgE0Lw40cY2YeNobEDWfYGA4zbmMGaskxAGo5nMAgwYBVizxIy59/EC0Hf86pR9bC/gGr30FagL4GaznA23AYWQsPVlsMb6QVM/b2SSTO7AE6jOfYcR5JkJaEc88M23hyCrBpkbuRvJnhxzebxH4eNuaPP2qq5fhu5xh/+FB2R56f/fgGrN6HBhwaPwGI2fCoHwWjYBSMglGAHwAAu2hiIQYvZKwAAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0001-5080-1285","institution":"Environment and Climate Change Canada","correspondingAuthor":true,"prefix":"","firstName":"Andrea","middleName":"Rose","lastName":"Norris","suffix":""},{"id":303567158,"identity":"9a4c16af-7e24-4442-a5cb-3a757e8b6f26","order_by":1,"name":"Kathy Martin","email":"","orcid":"","institution":"The University of British Columbia Faculty of Forestry","correspondingAuthor":false,"prefix":"","firstName":"Kathy","middleName":"","lastName":"Martin","suffix":""}],"badges":[],"createdAt":"2024-05-02 20:37:06","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4360933/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4360933/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":57367757,"identity":"00d7bbcc-2e99-4d8b-89f7-4eba61e7825b","added_by":"auto","created_at":"2024-05-29 17:34:39","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":190962,"visible":true,"origin":"","legend":"\u003cp\u003ePredicted changes in aggressive responses of mountain chickadees and red-breasted nuthatches to conspecific and heterospecific intruders with a dual pulse of mountain pine beetle abundance and nest cavities. Competitive interactions increase with resource availability through greater incentive to defend high quality resources and obtain greater potential reproductive benefits (Territory Investment Hypothesis; TIH; Fig 1a; (Brown 1964; Petit and Petit 1996; López-Segoviano et al. 2018)). Increased intra-specific competition but decreased inter-specific competition may result from expanded niche breadths that occur with pulsed resources, and interspecific dominance hierarchies are relaxed such that the social network resembles an egalitarian society with reductions in inter-specific dominance of resource specialists over generalists (Fig 1b, Ecological Niche Hypothesis; ENH; (Morse 1974; Chase and Leibold 2009; Chase 2011; Krams et al. 2020)). Finally, Fig 1c depicts a scenario where both intra- and inter-specific competition may decrease if individuals use the presence of conspecifics (Stamps 1988) or heterospecifics with the same habitat requirements (Mönkkönen et al. 1990) to assess territory quality in unpredictable environments. (The Competitor Attraction Hypothesis; CAH).\u003c/p\u003e","description":"","filename":"Fig11.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4360933/v1/9b98fd5ac212b87edbde7985.jpg"},{"id":57367755,"identity":"49f82746-c7c3-40a1-a0c2-e9256ecac59d","added_by":"auto","created_at":"2024-05-29 17:34:39","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":260388,"visible":true,"origin":"","legend":"\u003cp\u003eAnnual variation in median closest distance approached by a) mountain chickadees, and b) red-breasted nuthatches to conspecific and heterospecific intruders, with overall means indicated by dashed lines, across 974 intrusion experiments conducted at 25 sites in interior British Columbia. Round brackets indicate the total number of responses elicited, and square brackets show the total number of intruder trials in each year, boxes show data within the 75\u003csup\u003eth\u003c/sup\u003e percentiles, whiskers show the maximum and minimum within the 90\u003csup\u003eth\u003c/sup\u003e percentiles, and circles show outliers.\u003c/p\u003e","description":"","filename":"Fig12.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4360933/v1/c9074e0c8d4b4beb9d4b257a.jpg"},{"id":57368168,"identity":"500d5354-ea3d-4b2a-bc3b-5c4ab27a9c45","added_by":"auto","created_at":"2024-05-29 17:42:39","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":227490,"visible":true,"origin":"","legend":"\u003cp\u003eMean closest distance approached by respondent a) mountain chickadees and b) red-breasted nuthatches, to chickadee (CM) and nuthatch (NM) intruders across sites and years with increasing levels of beetle abundance, at active (solid lines) and inactive (dashed lines) nests occupied by conspecifics, in interior British Columbia, during 2004-2008 (2004 excluded in Figure 3b). Lines were generated from the linear models: Distance ~ Beetle (Be) + Plot type (PT) + Be x PT (see Tables 2,3), and responses were noted from any individual respondents observed within a 50m radius of the simulated intrusion.\u003c/p\u003e","description":"","filename":"Fig13.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4360933/v1/c2a6186936dad476d2562e14.jpg"},{"id":59162180,"identity":"3d391576-1f5f-4d9f-aa76-fa8ca7b996fa","added_by":"auto","created_at":"2024-06-27 05:40:25","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1375702,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4360933/v1/f6c75d4e-8bbe-427e-a874-17e77ff770f1.pdf"},{"id":57367758,"identity":"fb1f17d7-cf3b-48a0-a0ca-4813307c8ebc","added_by":"auto","created_at":"2024-05-29 17:34:39","extension":"csv","order_by":7,"title":"","display":"","copyAsset":false,"role":"supplement","size":1227751,"visible":true,"origin":"","legend":"","description":"","filename":"Playbackdatasubmit.csv","url":"https://assets-eu.researchsquare.com/files/rs-4360933/v1/4ba0f728e16147a3c56a1251.csv"}],"financialInterests":"","formattedTitle":"Natural resource pulses influence social-network dynamics: experimental evidence from a tree cavity-dependent bird community","fulltext":[{"header":"Significance Statement","content":"\u003cp\u003eLinks between social and ecological resilience may be important for animal societies, particularly as future generations experience rapid environmental change. Opportunities to evaluate how major environmental disruptions, such as resource pulses affect social networks in natural settings are extremely rare. By simulating territorial intrusions using song playbacks during and after a forest insect outbreak that resulted in a dual pulse of food and nest cavities for forest birds, we demonstrate that dominance hierarchies previously thought to govern year-round co-occurrence in chickadees and nuthatches can be reversed with increases in food resources for the typically dominant species (nuthatch). Our result that environmental variation allowed for plasticity in dominance hierarchies provides evidence that co-existence can be maintained through facilitative relationships (nuthatches providing nesting resources, and chickadees providing predator vigilance) between species that otherwise compete for food and nesting resources.\u003c/p\u003e"},{"header":"Introduction","content":"\u003cp\u003eAssessing the resiliency of social networks and predicting the responses of animal social systems to ecological change are emerging information needs in ecology (Shizuka and Johnson \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Strauss and Shizuka \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Coppinger et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Many ecological and evolutionary processes are dependent on social networks that are affected by the biotic and abiotic contexts in which they occur (Thompson \u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e1988\u003c/span\u003e; Chamberlain et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Krams et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Environmental change can destabilize existing social structures, leading to variable responses in social behaviour (Fisher et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Resource pulses \u0026ndash; brief, occasional, and intense events of high resource availability - may permeate through multiple levels of terrestrial and aquatic food webs to influence social networks (Ostfeld and Keesing \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Yang et al. \u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; St Clair et al. \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Examining thresholds of ecological change that lead to shifts in social network structure can help to reveal links between social and ecological resilience (Ilany and Akcay \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Studies of the effects of resource pulses on the variation in species interactions may help to fill key gaps in the functional dynamics of community ecology (Agrawal et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). In particular, there have been recent calls for more information on social networks and dominance hierarchies among multi-species groups (Coppinger et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Variation in foraging niches within and among species has been shown to affect variation in social network structure (Feinsinger and Colwell \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e1978\u003c/span\u003e; L\u0026oacute;pez-Segoviano et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), a relationship demonstrated previously with experimentally pulsed resources (St Clair et al. \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) but the opportunity to explore how natural resource pulses affect social interactions across species is rare.\u003c/p\u003e \u003cp\u003eForest bird communities are structured around complex social networks at the trophic and nidic levels, with species groups observed to be structured according to foraging and nesting guilds, respectively (Morse \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e1977\u003c/span\u003e; Martin et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Sridhar et al. \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; van der Hoek et al. \u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). In temperate regions, tits/chickadees (Paridae), nuthatches (Sittidae), and woodpeckers (Picidae) are among the bird species groups most frequently studied with respect to social networks due to their co-occurrence in both foraging and nesting guilds (Morse \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e1977\u003c/span\u003e; Martin et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). Chickadees show a great diversity of foraging behaviours as insect generalists, and while all species require tree cavities for nesting, some species are considered secondary cavity nesters as they do not typically excavate their cavities (Otter \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; McCallum et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Nuthatches are bark beetle-foraging specialists that are facultative excavators (I.e., they exhibit flexibility as they may excavate a new nesting cavity or use an existing cavity and are hereafter considered, excavators) (Matthysen \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e1998\u003c/span\u003e; Otter \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). These differences in partitioning the foraging and nesting niches, (i.e., resource specialization) within the cavity-nesting community is hypothesized to allow for co-occurrence driving patterns in year-round coexistence (Martin et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Chase and Leibold \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). Species considered to be resource specialists are often stronger competitors due to their stronger reliance of some shared but limited resource (Chase and Leibold \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2009\u003c/span\u003e); thus cavity limitation can drive competitive interactions among secondary cavity nesters (Aitken and Martin \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2008\u003c/span\u003e) and bark beetle limitation could drive competitive interactions among bark beetle specialists. Community ecology lacks studies that experimentally test whether patterns in co-occurrence indicate ecological interactions driving community co-existence (Blanchet et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) but a dual resource pulse of both bark beetles and nesting cavities offers a unique opportunity to explore coexistence among species that vary in their specialization to each resource.\u003c/p\u003e \u003cp\u003eDespite the niche differentiation nuthatches are found to be consistently dominant behaviourally over chickadees (Bock \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e1969\u003c/span\u003e; Otter \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2007\u003c/span\u003e) with some exceptions reported (Waite and Grubb \u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e1988\u003c/span\u003e). Both species exhibit aggressive behaviour towards conspecific and heterospecific individuals that threaten access to mates or food, which includes dominant individuals moving toward and supplanting their adversaries, and aggressive calls and displays that are unique to each species (Minock \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e1972\u003c/span\u003e; Waite and Grubb \u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e1988\u003c/span\u003e). Socially, chickadees give alarm calls when predators are present, which nuthatches recognize and use to avoid predators (Templeton and Greene \u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Carlson et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). In addition, chickadees use nesting cavities excavated by nuthatches, and their breeding populations show lagged positive functional and numerical responses to nuthatch densities (Aitken et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; Norris et al. \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2013\u003c/span\u003e, \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Due to their shared reliance on common resources and year-round co-occurrences including overlapping breeding territories and in rare instances nesting in the same tree cavity in the same year (Robinson et al. \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2005\u003c/span\u003e), chickadees and nuthatches provide an excellent model in which to examine how a dual resource pulse in insect food and tree cavities affects their social network.\u003c/p\u003e \u003cp\u003ePreviously, we reported that chickadees used more cavities excavated by nuthatches, as nuthatches had excavated proportionately more new nest cavities in response to the food resource pulse of a forest insect (Mountain Pine Beetle, \u003cem\u003eDendroctonus ponderosae\u003c/em\u003e), (Norris and Martin \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2010\u003c/span\u003e, \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Norris et al. \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2013\u003c/span\u003e, \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2022\u003c/span\u003e)). Here we used an experimental approach to infer the nature and strength of interactions within a population and between coexisting species (Martin et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e1996\u003c/span\u003e; Martin and Martin \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2001\u003c/span\u003e) to explore how changes in social network dynamics may have contributed to the observed plasticity in nesting behaviour that led to increased reproductive output for both species (Norris and Martin \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Norris et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Specifically, we examine temporal variation in intra- and inter-specific interactions of mountain chickadee and red-breasted nuthatch, two small cavity-nesting competitors that show plasticity in their nest excavation behaviours and foraging strategies (on bark beetles). The identity of intruders often plays an important role in territoriality, particularly with respect to their relationship to the territory occupant such that neighbours and non-neighbours, or strangers, can elicit different responses depending on various factors such as environmental conditions and life history characteristics (Ydenberg et al. \u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e1988\u003c/span\u003e; Eason and Hannon \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e1994\u003c/span\u003e; M\u0026uuml;ller and Manser \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Werba et al. \u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). For example, individuals that breed at lower densities and/or with sparse food resources can show higher aggression to territorial intrusions by novel intruders (strangers; dear enemy effect) relative to familiar intruders (neighbours), and individuals breeding at higher densities and/or with abundant food can show higher aggression to neighbours (nasty neighbour effect; (Yoon et al. \u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e2012\u003c/span\u003e)). We simulated territorial intrusions of conspecifics and heterospecifics to determine how the bark beetle outbreak and other environmental factors influenced the response of chickadees and nuthatches to territorial invaders. We evaluated our results with respect to three competing hypotheses suggested to influence species interactions (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Aggressive responses are predicted to: a) increase with increasing beetle abundance as the energy and potential reproductive benefits for individuals to defend high quality sites increases (Territory Investment Hypothesis), b) decrease towards heterospecifics but increase towards conspecifics, by expanding niche breadth, and reducing inter-specific dominance of resource specialists over generalists (Ecological Niche Hypothesis), or; c) decrease towards both species as individuals use the presence of conspecifics or heterospecifics with similar habitat requirements to assess territory quality (The Competitor Attraction Hypothesis). For example, if resource pulses impact these social networks according to the Territory Investment Hypothesis in which high quality resources are defended more aggressively, then intra- and inter-specific aggression among chickadees and nuthatches would both increase with higher beetle availability. The Ecological Niche Hypothesis (intra-specific mate competition is higher when inter-specific competition for the resources that most limit both species is low, (Chase and Leibold \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2009\u003c/span\u003e)) predicts that intra-specific aggression would increase with increasing beetle abundance, and inter-specific dominance of nuthatches over chickadees would be reduced. Alternatively, the Competitor Attraction Hypothesis in which tolerance of competitors increases as food resources are more abundant, predicts that both intra- and inter-specific aggression would decline with increasing beetle abundance (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStudy area\u003c/h2\u003e \u003cp\u003eWe studied behaviour, fecundity, and habitat characteristics of cavity-nesting birds in 25 mixed coniferous-deciduous forest stands on the lands of the Tŝilhqot\u0026rsquo;in, Secw\u0026eacute;pemc, and Southern Dakelh Peoples, an area surrounding Williams Lake, British Columbia, Canada (51\u0026deg;52\u0026rsquo;N, 122\u0026deg;21\u0026rsquo;W), from 2004\u0026ndash;2008. The predominant coniferous trees were Douglas-fir (\u003cem\u003ePseudotsuga menziesii\u003c/em\u003e var. \u003cem\u003eglauca\u003c/em\u003e), lodgepole pine (\u003cem\u003ePinus contorta\u003c/em\u003e var. \u003cem\u003elatifolia\u003c/em\u003e; hereafter, pine), and white and Engelmann hybrid spruce (\u003cem\u003ePicea glauca x engelmannii\u003c/em\u003e; Meidinger and Pojar 1991). The predominant broadleaf tree was trembling aspen (\u003cem\u003ePopulus tremuloides\u003c/em\u003e). Study sites ranged from 15 to 32 ha (one 7-ha site) in size and varied in composition from continuous forest to five sites that comprised a series of \u0026lsquo;forest groves\u0026rsquo; (0.2 to 5 ha) within a grassland matrix.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eStudy system\u003c/h2\u003e \u003cp\u003eThe small tree cavity nesting community comprised two species of insectivorous excavators and one secondary cavity nester (Martin and Eadie \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e1999\u003c/span\u003e). As many cavity excavators are also insectivores, large-scale insect outbreaks can lead to dual pulses in food and nest sites, potentially influencing the competitive interactions among tree cavity-dependent insectivores. Mountain pine beetle is a bark-boring insect that feeds on the phloem of pine trees and is a common disturbance agent in temperate forests that undergoes occasional patchy outbreaks in western North American forests (Taylor and Carroll \u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). Recent mountain pine beetle outbreaks in British Columbia increased year-round food availability, and subsequently, population densities of many insectivorous birds, including many excavators (Taylor and Carroll \u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; Martin et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). mountain chickadee (\u003cem\u003ePoecile gambeli\u003c/em\u003e), a secondary cavity nester (cavity specialist) that relies on excavators and natural decay processes for nest cavities, is primarily a foliage gleaner, but can switch to other foraging substrates depending on forest insect abundance (McCallum et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Red-breasted nuthatch (\u003cem\u003eSitta canadensis\u003c/em\u003e), is a facultative tree cavity nesting excavator, and is primarily a bark forager (Ghalambor and Martin \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe mountain pine beetle outbreak led to increases in population densities of both chickadees and nuthatches. Red-breasted nuthatch shifted nest site preference from areas of high nest site availability to those of high mountain pine beetle availability, where they excavated a greater proportion of nests (Norris and Martin \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2008\u003c/span\u003e, \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Mountain chickadee populations showed a one-year lag in increases following increased nuthatch populations, and used a greater proportion of smaller, safer nuthatch cavities following the beetle outbreak, suggesting that chickadee populations benefited from the higher densities of nuthatches (Norris et al. \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2013\u003c/span\u003e, \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). However, the beetle outbreak also led to increased population densities of a common nest predator for chickadees and nuthatches, American red squirrel (\u003cem\u003eTamiasciurus hudsonicus\u003c/em\u003e;(Martin and Norris \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2007\u003c/span\u003e)). Because increased predator presence can lead to reduced parental activity around the nest resulting in reduced fecundity (Fontaine and Martin \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2006\u003c/span\u003e), high squirrel densities may diminish territory quality and impede territory defence strategies. Such changes in territory characteristics could lead to increases or decreases in agonistic behaviour within and between species.\u003c/p\u003e \u003cp\u003eWe located nest trees of chickadees and nuthatches by checking all nesting cavities in trees used by other cavity-nesters in previous years (1995\u0026ndash;2007) with a camera monitoring system on an extendable pole and by following individuals to their nests. We considered nests to be active if we found eggs or chicks in a cavity and monitored all nests until fledging or failure. Additional study area and nest monitoring details are given in (Martin and Eadie \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e1999\u003c/span\u003e; Aitken et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2002\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eTerritorial intrusions\u003c/h2\u003e \u003cp\u003eWe used song playbacks with intruder simulations to investigate interference competition within and between species (Martin et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e1996\u003c/span\u003e) during territory establishment and before eggs were laid until after chicks fledged, between 1 May and 30 June, during (2004\u0026ndash;2005) and after (2006\u0026ndash;2008) the beetle outbreak (i.e., five years of measurement). To examine territorial responses of chickadees and nuthatches we simulated conspecific and heterospecific intrusions at six treatment types that represented two temporal- and two spatial-scales with respect to nesting (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). We simulated intrusions within ~\u0026thinsp;1 m of nest trees at nests that were active with either chickadees or nuthatches in the year of the presentation (1. active chickadee nest, 2. active nuthatch nest), 3. Nest cavities that were active in a previous year by either species (inactive nest), or within ~\u0026thinsp;1 m of a tree suitable for excavation or nesting (aspen tree\u0026thinsp;\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003e\u0026ge;\u003c/span\u003e\u0026thinsp;15cm DBH, with or without existing tree cavities) but was not to our knowledge used for nesting by either species, and located in a random direction\u0026thinsp;~\u0026thinsp;50m away from an active nest but still within the active territory (4. active chickadee territory, 5. active nuthatch territory) or 6. ~50m from an inactive nest within a territory not used by either chickadees or nuthatches in the year of the experiment (inactive territory). We compared responses of chickadees and nuthatches measured at each active, inactive, and suitable nest tree to those at suitable nest trees\u0026thinsp;~\u0026thinsp;50 m from inactive nests (inactive territory) to assess the level of territorial aggression. The two species exhibit unique behaviours with respect to aggressive calls and displays, but both species exhibit the same behaviour of moving towards and supplanting intruders (Minock \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e1972\u003c/span\u003e; Grava et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Therefore, we measured response to intruders by estimating the closest distance (m) that a respondent approached each intruder during each simulated intrusion to examine a common behaviour and compare interspecific responses (Kershner and Bollinger \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e1999\u003c/span\u003e). Although it was not possible to record data blind because our study involved focal animals in the field, we simulated intrusions of both species for each trial and presented each species in a random order. In 2004, we used song recordings from the second edition (1992) of the Peterson Field Guide audio compact disc from Cornell Lab of Ornithology, and during 2005\u0026ndash;2008, we used recordings of songs of local chickadees and nuthatches collected\u0026thinsp;~\u0026thinsp;20 km outside the study area. Songs were digitally manipulated so that each song was 2 min in length, and projected at similar volumes, then transferred onto a portable media player and broadcast over speakers. A taxidermic model specimen (intruder) of the appropriate species was placed on a wire stand\u0026thinsp;~\u0026thinsp;1m above the speakers and presented with the appropriate song type for each trial, with a 5-min period of silence following each intruder species presented. For each respondent, we recorded the species, individual (if colour banded), sex, time of day, behaviour (whether the respondent: called and call type, sang, swooped, attacked, etc.), and the closest distance (m) that they approached to the model intruder. In cases where the respondent attacked the intruder, and aggression levels remained high, we waited 10 min to start the presentation of the next intruder species until the aggressive individual returned to displaying the behaviour observed before the first intruder was presented. In 2004, mountain chickadees approached conspecifics farther than in other years except 2007 (F\u003csub\u003e4,251\u003c/sub\u003e=5.17, p\u0026thinsp;\u0026lt;\u0026thinsp;0.01), suggesting that the recordings of local chickadees elicited a stronger response from the Peterson\u0026rsquo;s recordings, so 2004 was excluded in analyses examining responses of mountain chickadees. Nuthatches approached conspecifics closer in 2004 relative to only 2008 (F\u003csub\u003e4,226\u003c/sub\u003e=5.34, p\u0026thinsp;\u0026lt;\u0026thinsp;0.01), therefore 2004 was included in all nuthatch analyses. Where intrusions were simulated at active nest territories, we visually inspected the nest cavity using a pole-mounted video camera, and recorded fecundity characteristics (number of eggs or nestlings) and the stage of the nest to determine breeding status (pre-nest, egg-laying, incubating, chick-rearing).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eWe conducted 974 territorial intrusion experiments according to six plot types (distance to nest tree, species using the cavity, and active or inactive nest status) assigned by mean distance to nest tree (m) observed to be occupied by a chickadee or nuthatch breeding pair (Territory holder species) in the same year as the experiment or in a previous year (active/inactive nest status, respectively). To test the additional hypothesis that proximity to nest affects territoriality we conducted simulations\u0026thinsp;~\u0026thinsp;50 m from active and inactive nests at (~\u0026thinsp;1 m from) any available tree suitable for excavation or nesting (aspen tree\u0026thinsp;\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003e\u0026ge;\u003c/span\u003e\u0026thinsp;15cm DBH) but which was never, to our knowledge, used by either species. We broadcasted song recordings paired with presentations of taxidermically prepared specimens of mountain chickadee and red-breasted nuthatch procured from the Beaty Biodiversity Museum at the University of British Columbia, Vancouver, to simulate intrusions at 25 study sites in interior British Columbia, Canada, from 2004\u0026ndash;2008. We compared the responses measured for each species at each active, inactive, and suitable nest tree to those at inactive territories.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePlot type\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDistance (m)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTerritory holder species\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNest status\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eActive chickadee nest (ACN)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003echickadee\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eactive\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eActive nuthatch nest (ANN)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003enuthatch\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eactive\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eInactive nest\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003echickadee and/or nuthatch\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003einactive\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eActive chickadee territory (ACT)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003echickadee\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eactive\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eActive nuthatch territory (ANT)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003enuthatch\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eactive\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eInactive territory\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eneither\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003einactive\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003ePopulation densities\u003c/h2\u003e \u003cp\u003eTo determine how population densities of conspecifics and heterospecifics (including predators) influenced the behavioural responses, we conducted point count surveys to estimate population densities per ha of mountain chickadee, red-breasted nuthatch, and red squirrel at 25 sites, during 2004\u0026ndash;2008. Point count stations were spaced within a 100 m square grid\u0026thinsp;\u0026ge;\u0026thinsp;50 m from a grassland or wetland edge (one station ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) in continuous forest sites, and at least 100 m apart in forest groves. From 0500\u0026ndash;0930 hours, we recorded the species, and number of individual birds and squirrels detected within 50-m radius 6-min point counts at each station (7\u0026ndash;32 stations site\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). Each station across the 25 sites was surveyed three times (rounds) in each of the 5 years. We divided the total number of individuals observed on all rounds by the total number of point counts to obtain estimates of mean individuals ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for each site and year. Further details of population monitoring methods were reported in earlier studies (Martin and Eadie \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e1999\u003c/span\u003e; Norris and Martin \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2010\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eVegetation surveys\u003c/h2\u003e \u003cp\u003eTo determine whether spatial and temporal variation in food and nest site availability influenced species interactions, we established 0.04-ha circular vegetation plots centered at each point count station every year during 2004\u0026ndash;2008. For all trees \u0026ge;12.5 cm diameter at breast height (DBH; measured at 1.3 m above ground) in each plot, we recorded tree species, DBH, general health (e.g., presence of boring insects on the bole), and decay class. Decay class 1 was a live, healthy tree, 2 a live tree with visible sign of bark boring insects or heart rot fungus, and 3\u0026ndash;8 were standing dead trees in progressive states of decay (Thomas \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e1979\u003c/span\u003e). Before and during the study period, an outbreak of mountain pine beetle occurred across all sites, with incidence of beetle attacks on pines increasing sharply after 2002, and by 2005 over 95% of the mature lodgepole pine trees (40% of the trees on the sites) were dead (Edworthy et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). However, the onset of the beetle outbreak showed temporal and spatial variation in the number of trees showing sign of beetle attack (Drever et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). Therefore, we could examine the effects of beetle abundance at the site-year level. Beetle eggs are laid beneath the bark in late summer where they overwinter and beetle larvae complete development in the following summer before emerging as adults (Reid \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e1962\u003c/span\u003e). Thus, beetle larvae provided a rich food source throughout the winters and following breeding seasons for insectivores. We determined beetle-infected pine densities as the total number of decay class 2 pine trees with bark boring insects, which was evident by the presence of dried resin outflows, or small entry holes (~\u0026thinsp;2mm in diameter) on the bark, expressed on a per ha basis divided by the total number of 0.04 ha vegetation plots, for each site and year. Since over 90% of chickadee and nuthatch nests were in aspen trees (Martin and Eadie \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e1999\u003c/span\u003e), we determined the densities of potential nest trees per ha from number of aspen trees divided by the total number of 0.04 ha plots, for each site and year.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analyses\u003c/h2\u003e \u003cp\u003eWe examined how territory characteristics (proximity to active and inactive nests, food and nest site availability, and population densities of conspecifics, and heterospecifics, including squirrels) influenced intra- and inter-specific aggression of chickadees and nuthatches. We used the closest distance (m) that a respondent approached each intruder during the territory intrusion simulation as the metric of aggression. For both species, the data for closest distance approached were heavily skewed toward zero and showed an uneven distribution in the number of response variables between 0\u0026ndash;50 m. As a result of the truncated normal distribution and the high number of zero values, we applied a mixture of the binomial (for closest distance\u0026thinsp;=\u0026thinsp;0 or \u0026gt;\u0026thinsp;0) and left-truncated normal (for closest distance\u0026thinsp;\u0026gt;\u0026thinsp;0) distributions. We used linear mixed-effects models (Crawley \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2012\u003c/span\u003e) to examine how variation in closest distance approached was explained by the fixed-effects variables: intruder species (conspecific or heterospecific), plot type of the experiment (active chickadee nest; ACN, active nuthatch nest; ANN, inactive nest, active chickadee territory; ACT, active nuthatch territory; ANT, or inactive territory), breeding status of territory owners (if on an active nest plot), presentation sequence of intruders, and abundance of food (beetle-infected live pine densities per ha for the corresponding site and year in which the intrusion experiment was conducted) and nest sites (nest-tree densities per ha), and densities per ha of red-breasted nuthatch, mountain chickadee, and red squirrel, and all biologically relevant secondary interaction terms. Because we conducted intrusion experiments at multiple locations (plots) within sites and at multiple sites within years, we included plot nested within site as a random effect to account for the hierarchical error structure due to the repeated measures, in all models. Since the repeated measures were not evenly spaced within and between plots, we added a continuous autoregressive correlation within plots. These hierarchical errors were assumed to have normal distributions.\u003c/p\u003e \u003cp\u003eWe used penalized quasi-likelihood (PQL) methods to generate parameter estimates (Bolker et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). We used Wald\u0026rsquo;s t-test to eliminate fixed-effects variables from fully parameterized models, and to determine whether fixed-effect variables had a significant effect on the response variables given the other fixed-effect variables and the hierarchical error structure in the best-fit (final) model (Bolker et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). Negative signs of significant coefficients indicated that the closest distance approached decreased (I.e., the responding bird approached closer to the model, and was more aggressive) and positive signs indicated that distance approached increased (the bird approached further distances, and was less aggressive) with increases in the fixed effect variables (Crawley \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2012\u003c/span\u003e)). Penalized quasi-likelihood estimates were obtained using the function glmmPQL in the library MASS, and all data analyses were conducted in the program R version 2023.06.1 (R Core Team 2013; Ripley et al. \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2013\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eWe simulated 974 territorial intrusions across 25 sites, during 2004\u0026ndash;2008. We detected 397 responses (i.e., at least one adult detected\u0026thinsp;\u0026lt;\u0026thinsp;50 m from intruder) from the bark beetle generalist, mountain chickadee, and 372 responses from red-breasted nuthatch (bark beetle specialist). In 95 cases (23.9%) for mountain chickadees and in 30 cases (8.1%) for red-breasted nuthatch, respondents struck the intruder, knocking it to the ground, and then repeatedly attacked the intruder until the observer removed it. Overall, both species approached intruders closer when simulations were conducted on active nest plots (~\u0026thinsp;1m from nest tree; ACN, ANN) compared to inactive territories and nuthatches also approached closer at suitable nest trees located\u0026thinsp;~\u0026thinsp;50m away from active nests (active nuthatch territories; ANT) than those in inactive territories. Both species showed similar responses to conspecific intruders (mean closest distance approached: mountain chickadee, 9.1 m\u0026thinsp;\u0026plusmn;\u0026thinsp;0.77 SE; Nuthatch, 11 m\u0026thinsp;\u0026plusmn;\u0026thinsp;0.80 SE), but mountain chickadees approached heterospecific intruders significantly closer than did nuthatches (14 m\u0026thinsp;\u0026plusmn;\u0026thinsp;1.1 SE, and 21m\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2 SE, respectively; Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003e). During the beetle outbreak (2004\u0026ndash;2006), both species approached closer than the overall mean, and approached heterospecifics at least as close as the overall mean approach to conspecifics. After the beetle outbreak (2007\u0026ndash;2008) neither species approached the intruder as close as those respondents measured during the beetle outbreak.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMountain chickadee responses to conspecific and nuthatch territorial intruders across 112 plots at 25 sites in interior British Columbia, from 2005\u0026ndash;2008. Parameter estimates (Estimate), standard errors (SE), and degrees of freedom (DF) of the final mixture distribution (normal and binomial), linear mixed-effects model, generated using penalized quasi-likelihood of closest distance approached by mountain chickadees to simulated intruders of red-breasted nuthatch (NM) and mountain chickadee (CM) at various locations (plots) within territories compared to inactive territories, with spatial and temporal variation in beetle abundance (beetle-infected pine densities; Be), and nuthatch densities. Estimates were generated from the final model, Closest distance\u0026thinsp;~\u0026thinsp;Intruder\u0026thinsp;+\u0026thinsp;Beetle density (Be)\u0026thinsp;+\u0026thinsp;Chickadee density\u0026thinsp;+\u0026thinsp;Nuthatch density\u0026thinsp;+\u0026thinsp;Plot type (PT)\u0026thinsp;+\u0026thinsp;Be\u003cdiv description=\"\" class=\"Drawing\" id=\"22\" name=\"Picture 30\"\u003e\u003c/div\u003ePT; random effects\u0026thinsp;=\u0026thinsp;Site / Plot ID, with continuous autoregressive correlation within Plot ID. Fixed effect variables had significant effects on distance approached to intruders where p\u0026thinsp;\u0026lt;\u0026thinsp;0.1, in bold. Although the responses in five classes of plot type were compared to those in random plots in inactive territories, only classes with significant effects are listed.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFixed Effect\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eEstimate\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSE\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDF\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003et-value\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003ep-value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eModel Intercept\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e211\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e5.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eNuthatch model (NM; relative to CM)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e211\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026thinsp;0.002\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eBeetle-infected pine density (Be)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e130\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e211\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e0.076\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eChickadee density\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-8.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e211\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e0.073\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eNuthatch density\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e211\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e0.041\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003ePT: Active chickadee nest (ACN)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e211\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-3.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e0.0002\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eBe x ACN interaction\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-140\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e211\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e0.052\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eRed-breasted nuthatch responses to conspecific and chickadee territorial intruders across 114 plots at 25 sites in interior British Columbia, from 2004\u0026ndash;2008. Parameter estimates (Estimate), standard errors (SE), and degrees of freedom (DF) of the final mixture distribution (normal and binomial), linear mixed-effects model generated using penalized quasi-likelihood for closest distance approached by red-breasted nuthatches to simulated intruders of red-breasted nuthatch (NM) and mountain chickadee (CM), at various locations (plots) within active territories compared to inactive territories with spatial and temporal variation in beetle abundance (beetle-infected pine densities; Be), and Nuthatch densities. Estimates were generated from the final model, Closest distance\u0026thinsp;~\u0026thinsp;Intruder\u0026thinsp;+\u0026thinsp;Beetle (Be)\u0026thinsp;+\u0026thinsp;Nuthatch density\u0026thinsp;+\u0026thinsp;Plot type (PT)\u0026thinsp;+\u0026thinsp;Be \u003cdiv description=\"\" class=\"Drawing\" id=\"1454743877\" name=\"Picture 1454743877\"\u003e\u003c/div\u003e PT; random effects\u0026thinsp;=\u0026thinsp;Site/Plot ID, with continuous autoregressive correlation within Plot ID. Fixed-effect variables with significant effects on distance approached to intruders where p\u0026thinsp;\u0026lt;\u0026thinsp;0.1, given in bold. Although responses in five classes of plot type were compared to those in inactive territories, only classes with significant effects are listed.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFixed Effect\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eEstimate\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSE\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDF\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003et-value\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003ep-value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e(Intercept)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e157\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eNuthatch model (relative to CM)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e157\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-8.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026thinsp;0.001\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBeetle-infected pine density (Be)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e157\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.89\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.37\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eNuthatch density\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e9.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e157\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e0.021\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePT: Active nuthatch territory (ANT)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-4.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e157\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.13\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003ePT: Active nuthatch nest (ANN)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e157\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-4.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026thinsp;0.001\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eBe x ANT interaction\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e157\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-1.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e0.098\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eBe x ANN interaction\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-37\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e157\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e0.08\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003eMountain chickadee\u003c/h2\u003e \u003cp\u003eOn average, chickadees approached all intruders closest at experiments conducted in the immediate proximity of (~\u0026thinsp;1 m from) active chickadee nests (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) and conspecific intruders closer than heterospecific intruders, (\u003cem\u003eβ\u003c/em\u003e\u003csub\u003e\u003cem\u003eNM\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;6.4\u0026thinsp;\u0026plusmn;\u0026thinsp;1.5 SE), which supported the Ecological Niche Hypothesis. However, as beetle abundance increased (2005 and 2006), chickadees approached heterospecific intruders closer than conspecific intruders at active chickadee nests (\u003cem\u003eβ\u003c/em\u003e\u003csub\u003e\u003cem\u003eBexACN\u003c/em\u003e\u003c/sub\u003e= -140\u0026thinsp;\u0026plusmn;\u0026thinsp;70 SE; Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003e), supporting the Territory Investment Hypothesis (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Chickadees showed a nasty neighbour effect towards conspecifics, approaching intruders closer with increasing chickadee densities, but a dear enemy effect towards nuthatches, approaching farther with increasing nuthatch densities.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eRed-breasted nuthatch\u003c/h2\u003e \u003cp\u003eConsistent with the Ecological Niche Hypothesis, the final model describing variation in the closest distance approached to intruders predicted that nuthatches approached conspecifics closer than to chickadees (\u003cem\u003eβ\u003c/em\u003e\u003csub\u003e\u003cem\u003eNM\u003c/em\u003e\u003c/sub\u003e = -12 1.5 SE; Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Nuthatches showed a dear enemy effect towards conspecifics, approaching intruders farther with increasing nuthatch densities. The relationship between response distance and beetle abundance depended upon whether the nest plot was active or inactive: Consistent with the Territory Investment Hypothesis, nuthatches approached intruders closer with increasing beetle abundance in active nuthatch territories (both at active nests and suitable nest trees\u0026thinsp;~\u0026thinsp;50m from the nest; \u003cem\u003eβ\u003c/em\u003e\u003csub\u003e\u003cem\u003eBexANN\u003c/em\u003e\u003c/sub\u003e = -37 21 SE, \u003cem\u003eβ\u003c/em\u003e\u003csub\u003e\u003cem\u003eBexANT\u003c/em\u003e\u003c/sub\u003e = -44 26 SE, respectively), compared to suitable nest trees in inactive territories that were unoccupied by both chickadees and nuthatches in the year of the experiment.\u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eWe found support for both the Ecological Niche and Territory Investment Hypotheses at different spatial and temporal scales. Chickadees showed greater annual variability in their responses and were more aggressive than nuthatches across all territories, sites, and years, consistent with the Ecological Niche Hypothesis. Nuthatches approached conspecific intruders twice as close as heterospecific intruders, overall, and approached intruders closest at both active nests and at suitable nest trees near active nuthatch nests (active nuthatch territories) relative to inactive territories. Both species were more aggressive to nuthatch intruders at active nest territories at sites and in years with increasing beetle abundance, suggesting that: 1) the more efficient beetle-foragers (nuthatches) may pose a greater threat to territory intrusion during beetle outbreaks, and 2) individuals increased their investment in territory defence with increases in food availability (Territory Investment Hypothesis).\u003c/p\u003e \u003cp\u003eAs with any experimental study design, our results are limited to those variables examined. Social networks are likely influenced by other factors affecting communication in animals such as demographic features, visual, auditory and other sensory cues such as vibrational signals (Hill \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2001\u003c/span\u003e; Erbe and Thomas \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), and the presence of other species including humans (Coppinger et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Our experimental approach of presenting a model and broadcasting auditory signals, although a standard approach to measuring behavioural responses might have influenced the ways in which these species normally interact with one another within this spatial and temporal context.\u003c/p\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eEcological niche hypothesis\u003c/h2\u003e \u003cp\u003eIn earlier work, we found that shifts in habitat and cavity preferences led to increases in reproductive output for both species, and hypothesized that increases in food availability could reduce territorial disputes (Norris et al. \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2013\u003c/span\u003e, \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Norris and Martin \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Our finding that responses to heterospecifics were stronger in chickadees than nuthatches (24% of responses by mountain chickadees led to an attack vs. 8% by nuthatches) is similar to another study approximately 300 km north of our study area, where mountain chickadees showed similar responses to conspecific intruders and to the behaviourally dominant heterospecific intruder, Black-capped chickadee (\u003cem\u003ePoecile atricapillus\u003c/em\u003e), a small cavity excavator (Grava et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Despite previous observations and generally accepted knowledge among titmice experts that nuthatches are behaviourally dominant over chickadees (Bock \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e1969\u003c/span\u003e; Kershner and Bollinger \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e1999\u003c/span\u003e; Otter \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2007\u003c/span\u003e), others occasionally have found chickadees or titmice to be socially dominant over nuthatches in foraging flocks (Waite and Grubb \u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e1988\u003c/span\u003e). Dhondt (Dhondt \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e1989\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2012\u003c/span\u003e) has even suggested that greater interspecific (relative to intraspecific) competition during the breeding season is an evolutionary balancing mechanism promoting year-round coexistence in tits. As with the Dhondt studies, chickadees in our study showed unexpectedly higher aggression to their dominant heterospecific competitor during the breeding season. Notably, most studies of dominance hierarchies in titmice are conducted outside the breeding season and where patterns in social dominance are inferred from mainly from access to food (Waite and Grubb \u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e1988\u003c/span\u003e; Ghalambor and Martin \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; McCallum et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2020\u003c/span\u003e), rather than breeding resource supply.\u003c/p\u003e \u003cp\u003eAt the nesting guild, nest cavity resource specialists, or those who have greater limitation to nest-sites can behaviourally dominate generalists (in this case, we refer to those species capable of excavating their own cavity; Aitken and Martin \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). For example, the secondary cavity nester, European starling (\u003cem\u003eSturnus vulgaris\u003c/em\u003e), can usurp cavities from excavating woodpeckers who also reuse cavities by initiating their nests before woodpeckers (Wiebe \u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; Frei et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Thus, Starlings are often considered a behaviourally dominant species in the nest web, often having negative impacts on breeding success of rivals through interference competition (Wiebe \u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; Aitken and Martin \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Frei et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Mountain chickadees initiated nests\u0026thinsp;~\u0026thinsp;15d earlier than nuthatches, suggesting that earlier nesting facilitated their dominance over nuthatches (Norris and Martin \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Norris et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). In the first year of our study we reported an instance of nest sharing between mountain chickadee and red-breasted nuthatch, with a female nuthatch displacing a chickadee pair during the nestling stage and successfully fledging both nuthatch and chickadee young from the nest (Robinson et al. \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2005\u003c/span\u003e) suggesting that chickadees have reproductive incentive to defend their nests against the more dominant heterospecific to prevent nest usurpation. Thus, our findings support the Ecological Niche Hypothesis and suggest that the dominance hierarchy between chickadees and nuthatches varies and can be reversed on breeding territories during resource pulses. These two species groups are the only cavity-nesting passerines to remain in boreal and hemi-boreal temperate regions during winter and due to their year-round co-occurrence and niche overlap probably have highly complex social networks and many other important social dynamics not tested here. Model systems where rank can be manipulated are suggested to be extremely useful for testing hypotheses about dominance network dynamics (Strauss and Shizuka \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). We suggest that future work should explore the generality of our findings that chickadees that are subordinate in foraging groups can become dominant to excavating nuthatches on breeding territories during resource fluctuations.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eCompetitor attraction hypothesis\u003c/h2\u003e \u003cp\u003eSince both species approached nuthatch intruders closest at active nest territories, it is possible that both species used nuthatches as cues in territory establishment and the distance approached to nuthatch intruders represented territory prospecting rather than defence. However, we found a significantly negative correlation between the elicited behaviour of attacking the model and distance approached to the model (In the simple linear model, Closest distance\u0026thinsp;~\u0026thinsp;Attacker vs. non-attacker, for chickadees, \u003csub\u003eA\u003c/sub\u003e = -13 m 1.8 SE, \u003cem\u003et\u003c/em\u003e = -6.8, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01, and nuthatches, \u003csub\u003eA\u003c/sub\u003e = -16 m 3.3 SE, \u003cem\u003et\u003c/em\u003e = -4.7, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01) suggesting that the closest distance approached indeed represented an aggressive response rather than a passive, exploratory response. Further, if individuals were using the presence of nuthatches to assess new territories, we would expect a closer approach to nuthatch intruders at all territories. Yet, both species approached similar distances to both nuthatch and chickadee intruders at heterospecific territories (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.1; Interaction effect of heterospecific nest plot and nuthatch intruder for both species), and the increased responses to nuthatch intruders were only observed at conspecific territories (Tables\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, \u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), indicating territorial defence responses. Since distance approached was correlated with an aggressive response, and both species approached intruders closer with increasing beetle abundance, neither intra- nor inter-specific aggression was reduced with increases in food availability, as was predicted under the competitor attraction hypothesis. Thus, we were able to reject both the conspecific and heterospecific attraction hypotheses for both chickadees and nuthatches.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eTerritory investment hypothesis\u003c/h2\u003e \u003cp\u003eBoth species showed an increasingly aggressive response to all intruders at active nest trees and nearby suitable nest trees within territories, with increasing beetle abundance, suggesting that investment in territorial defence increased with the beetle outbreak (or more accurately, investment declined with reductions in beetle availability at the temporal scale measured in this study). Food-supplemented song sparrows (\u003cem\u003eMelospiza melodia\u003c/em\u003e) in the northeastern United States were more aggressive to territorial intruders than non-supplemented birds, particularly in rural environments where birds were less aggressive overall and resources were potentially more limited relative to those in urban areas (Foltz et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). High levels of aggression and territorial defence often require elevated energy expenditures, but territories containing ample resources required for increased defence may also provide greater reproductive benefits as the energy spent on territorial defence is readily recouped (Martin 1987). In cavity-nesting Prothonotary Warblers (\u003cem\u003eProtonotaria citrea\u003c/em\u003e), pairs occupying higher quality territories produced more fledglings and competitively excluded other pairs from territories (Petit and Petit \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e1996\u003c/span\u003e). Mountain pine beetles provide a year-round food source from late summer when adult beetles lay eggs beneath the bark to the following summer when larval development is completed (Reid \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e1962\u003c/span\u003e). As both chickadees and nuthatches are winter residents, the beetle outbreak likely increased the energy reserves of individuals over winter and in spring before the breeding season. During the beetle outbreak, chickadees laid earlier and larger clutches, and had a higher probability of fledging nestlings, and nuthatches laid larger clutches later in the breeding season compared to before the outbreak (Norris and Martin \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Norris et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Thus, it is likely that territories with high beetle abundance provided more food resulting in earlier nesting and higher fecundity, leading to an increase in territoriality before and during territory establishment in both species.\u003c/p\u003e \u003cp\u003eOur result that chickadees approached intruders closer at sites and in years with increasing chickadee densities, supported the nasty neighbour effect that neighbouring conspecifics pose a greater threat than strangers due to higher potential for competition over resources and access to mates leading to positive density-dependent aggression (Brown \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e1964\u003c/span\u003e; Yoon et al. \u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Contrary to their response to conspecific densities, however, chickadees showed lower aggression with rising nuthatch densities. Nuthatches also showed lower aggression with rising nuthatch densities, and both species were most aggressive to nuthatch intruders in the years of lowest nuthatch population densities (2005\u0026ndash;2006; Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003e; (Norris and Martin \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2010\u003c/span\u003e)). Breeding populations of both chickadees and nuthatches showed high annual variability, and the result that aggression toward nuthatch intruders was higher when nuthatch densities were lowest and lower when densities were highest suggest that unfamiliar nuthatches (strangers) may pose a greater threat than neighbouring nuthatches, providing support for the \u0026lsquo;dear enemy\u0026rsquo; effect that both species were less aggressive towards familiar nuthatches (i.e., a known threat), and avoided the costs associated with repetitive territorial disputes. The result that chickadees could switch between the nasty neighbour effect to conspecifics and the dear enemy effect to nuthatches indicates behavioural plasticity in territoriality, a pattern shown to occur across the breeding season for dusky warblers (\u003cem\u003ePhylloscopus fuscatus\u003c/em\u003e) in Hebei, China (Wang et al. \u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). We provided evidence to support both the nasty neighbour and dear enemy effects in chickadees and nuthatches and suggest that future work examine how plasticity in territoriality across the year may contribute to the complex social networks and co-existence in this species group.\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eWe found that a cavity specialist and foraging generalist chickadee dominated nuthatch (a beetle specialist and cavity generalist), suggesting that inter-specific dominance hierarchies observed at foraging guilds can be reversed in the breeding season during resource pulses. Increases in intra- and inter-specific competition with increases in beetle abundance suggests that behavioural mechanisms governing community structure may change dramatically during resource pulses that increase the disparity in territory quality. Our observation that aggressive responses declined following the beetle outbreak, returning to the typically reported relationships among chickadees and nuthatches suggests that these social networks exhibit resiliency following resource pulses. Future work that further examines the variation in responses to conspecifics and heterospecifics and their associated fitness consequences within the context of resource limitation might reveal how social networks may regulate year-round coexistence among these species groups (Dhondt \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Coppinger et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e "},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll data generated or analyzed during this study are included in this published article (and its supplementary information files).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSupplementary Information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eBelow is the link to the electronic supplementary material.\u003c/p\u003e\n\u003cp\u003eSupplementary file1 (Playbackdata_submit.csv)\u003c/p\u003e\n\u003cp\u003eSupplementary file2 (Playbacks_submit.R)\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics declarations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePotential conflicts of interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe declare that we have no financial or non-financial competing interests to disclose.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResearch involving animal participants\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe followed all protocols required by the Animal Care Committees of the University of British Columbia and Environment and Climate Change Canada, under annually renewed permits from the University of British Columbia Animal Care Protocol and Environment and Climate Change Canada\u0026rsquo;s scientific permit and banding permit number 10365.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eInformed consent\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eBoth authors gave final approval for publication and agreed to be held accountable for the work performed therein.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;We are grateful for Tŝilhqot\u0026rsquo;in, Secw\u0026eacute;pemc, and Southern Dakelh Peoples for their historical and continued relationships with these lands and the other-than human relatives, with whom these studies were conducted. We are grateful for the chickadee and nuthatch relatives who were involved in this study. We thank the many field technicians who assisted in data collection, specifically D. Gunawardana, M. Marjanovic, I. Behret, M. Behret, H. Kenyon, M. Edworthy, and K. Scotton. D. Cockle built and maintained the cavity monitoring equipment. Scout Island Nature Society in Williams Lake, BC donated the specimens for the models used in territorial intrusions. Discussions with K. Aitken, K. Wiebe, and D. Shizuka helped to shape the behavioural field trials, and A. Boyle, D. Weary, and discussions with the Martin-Arcese Lab group improved the quality of the manuscript. V. LeMay, D. Irwin, J. McLean, and J. Goheen assisted in study design.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eStatements and Declarations\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eResearch grants were awarded to KM from the Natural Sciences and Engineering Research Council of Canada (NSERC), Environment and Climate Change Canada,\u0026nbsp;and Tolko Limited. ARN received post-graduate scholarships from NSERC, a Four-Year Doctoral Fellowship and a\u0026nbsp;Pacific Century Graduate Scholarship from the University of British Columbia, and research grants from the Forest Investment Account Forest Science Program (Graduate Student Pilot Project and Mountain Pine Beetle Initiative Graduate Research Fund), the Southern Interior Bluebird Trail Society, and a Junco Technologies Award from the Society of Canadian Ornithologists and Bird Studies Canada.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAgrawal AA, Ackerly DD, Adler F et al (2007) Filling key gaps in population and community ecology. Front Ecol Environ 5:145\u0026ndash;152\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAitken KEH, Martin K (2008) Resource selection plasticity and community responses to experimental reduction of a critical resource. Ecology 89:971\u0026ndash;980. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1890/07-0711.1\u003c/span\u003e\u003cspan address=\"10.1890/07-0711.1\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAitken KEH, Wiebe KL, Martin K (2002) Nest-Site Reuse Patterns for a Cavity-Nesting Bird Community in Interior British Columbia. Auk 119:391\u0026ndash;402. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1093/auk/119.2.391\u003c/span\u003e\u003cspan address=\"10.1093/auk/119.2.391\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBlanchet FG, Cazelles K, Gravel D (2020) Co-occurrence is not evidence of ecological interactions. Ecol Lett 23:1050\u0026ndash;1063. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1111/ele.13525\u003c/span\u003e\u003cspan address=\"10.1111/ele.13525\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBock CE (1969) Intra- vs. Interspecific Aggression in Pygmy Nuthatch Flocks. Ecology 50:903\u0026ndash;905. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.2307/1933706\u003c/span\u003e\u003cspan address=\"10.2307/1933706\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBolker BM, Brooks ME, Clark CJ et al (2009) Generalized linear mixed models: a practical guide for ecology and evolution. Trends Ecol Evol 24:127\u0026ndash;135\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBrown JL (1964) The evolution of diversity in avian territorial systems. Wilson Bull 160\u0026ndash;169\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCarlson NV, Greene E, Templeton CN (2020) Nuthatches vary their alarm calls based upon the source of the eavesdropped signals. Nat Commun 11:526. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1038/s41467-020-14414-w\u003c/span\u003e\u003cspan address=\"10.1038/s41467-020-14414-w\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChamberlain SA, Bronstein JL, Rudgers JA (2014) How context dependent are species interactions? Ecol Lett 17:881\u0026ndash;890. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1111/ele.12279\u003c/span\u003e\u003cspan address=\"10.1111/ele.12279\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChase JM (2011) Ecological niche theory. Theory Ecol 93\u0026ndash;107\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChase JM, Leibold MA (2009) Ecological niches: linking classical and contemporary approaches. University of Chicago Press\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCoppinger BA, Carlson NV, Freeberg TM, Sieving KE (2023) Mixed-species groups and the question of dominance in the social ecosystem. Philos Trans R Soc B Biol Sci 378:20220097. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1098/rstb.2022.0097\u003c/span\u003e\u003cspan address=\"10.1098/rstb.2022.0097\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCrawley MJ (2012) The R book. Wiley\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDhondt AA (1989) Ecological and Evolutionary Effects of Interspecific Competition in Tits. Wilson Bull 101:198\u0026ndash;216\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDhondt AA (2012) Interspecific competition in birds. Oxford Avian Biology\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDrever MC, Goheen JR, Martin K (2009) Species\u0026ndash;energy theory, pulsed resources, and regulation of avian richness during a mountain pine beetle outbreak. Ecology 90:1095\u0026ndash;1105\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEason P, Hannon S (1994) New birds on the block: new neighbors increase defensive costs for territorial male willow ptarmigan. Behav Ecol Sociobiol 34:419\u0026ndash;426\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEdworthy AB, Drever MC, Martin K (2011) Woodpeckers increase in abundance but maintain fecundity in response to an outbreak of mountain pine bark beetles. Ecol Manag 261:203\u0026ndash;210\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eErbe C, Thomas JA (2022) Exploring Animal Behavior Through Sound: Volume 1: Methods. Springer Nature\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFeinsinger P, Colwell RK (1978) Community Organization Among Neotropical Nectar-Feeding Birds. Am Zool 18:779\u0026ndash;795. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1093/icb/18.4.779\u003c/span\u003e\u003cspan address=\"10.1093/icb/18.4.779\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFisher DN, Kilgour RJ, Siracusa ER et al (2021) Anticipated effects of abiotic environmental change on intraspecific social interactions. Biol Rev 96:2661\u0026ndash;2693. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1111/brv.12772\u003c/span\u003e\u003cspan address=\"10.1111/brv.12772\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFoltz SL, Ross AE, Laing BT et al (2015) Get off my lawn: increased aggression in urban song sparrows is related to resource availability. Behav Ecol 26:1548\u0026ndash;1557. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1093/beheco/arv111\u003c/span\u003e\u003cspan address=\"10.1093/beheco/arv111\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFontaine JJ, Martin TE (2006) Habitat selection responses of parents to offspring predation risk: an experimental test. Am Nat 168:811\u0026ndash;818\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFrei B, Nocera JJ, Fyles JW (2015) Interspecific competition and nest survival of the threatened Red-headed Woodpecker. J Ornithol 156:743\u0026ndash;753\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGhalambor CK, Martin TE (2020) Red-breasted Nuthatch (Sitta canadensis). In: Billerman SM, Keeney BK, Rodewald PG, Schulenberg TS (eds) Birds of the World. Cornell Lab of Ornithology\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGrava A, Grava T, Otter KA (2012) Differential Response to Interspecific and Intraspecific Signals Amongst Chickadees. Ethology 118:711\u0026ndash;720. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1111/j.1439-0310.2012.02061.x\u003c/span\u003e\u003cspan address=\"10.1111/j.1439-0310.2012.02061.x\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHill PS (2001) Vibration and animal communication: a review. Am Zool 41:1135\u0026ndash;1142\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eIlany A, Akcay E (2016) Social inheritance can explain the structure of animal social networks. Nat Commun 7:12084\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKershner EL, Bollinger EK (1999) Aggressive Response of Chickadees Towards Black-Capped and Carolina Chickadee Calls in Central Illinois. Wilson Bull 111:363\u0026ndash;367\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKrams IA, Luoto S, Krama T et al (2020) Egalitarian mixed-species bird groups enhance winter survival of subordinate group members but only in high-quality forests. Sci Rep 10:4005. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1038/s41598-020-60144-w\u003c/span\u003e\u003cspan address=\"10.1038/s41598-020-60144-w\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eL\u0026oacute;pez-Segoviano G, Bribiesca R, Arizmendi MDC (2018) The role of size and dominance in the feeding behaviour of coexisting hummingbirds. Ibis 160:283\u0026ndash;292. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1111/ibi.12543\u003c/span\u003e\u003cspan address=\"10.1111/ibi.12543\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMartin K, Aitken KEH, Wiebe KL (2004) Nest Sites and Nest Webs for Cavity-Nesting Communities in Interior British Columbia, Canada: Nest Characteristics and Niche Partitioning. Condor 106:5\u0026ndash;19\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMartin K, Eadie JM (1999) Nest webs: A community-wide approach to the management and conservation of cavity-nesting forest birds. Ecol Manag 115:243\u0026ndash;257. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/S0378-1127(98)00403-4\u003c/span\u003e\u003cspan address=\"10.1016/S0378-1127(98)00403-4\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMartin K, Norris A (2007) Life in the small-bodied cavitynester guild: Demography of sympatric mountain and black-capped chickadees within nest web communities under changing habitat conditions. Ecol Behav Chickadees Titmice Integr Approach 111\u0026ndash;130\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMartin K, Norris A, Drever M (2006) Effects of bark beetle outbreaks on avian biodiversity in the British Columbia interior: Implications for critical habitat management. J Ecosyst Manag\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMartin PR, Fotheringham JR, Ratcliffe L, Robertson RJ (1996) Response of American redstarts (suborder Passeri) and least flycatchers (suborder Tyranni) to heterospecific playback: the role of song in aggressive interactions and interference competition. Behav Ecol Sociobiol 39:227\u0026ndash;235\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMartin PR, Martin TE (2001) Behavioral interactions between coexisting species: song playback experiments with wood warblers. Ecology 82:207\u0026ndash;218\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMatthysen E (1998) The nuthatches. A\u0026amp;C Black\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMcCallum DA, Grundel R, Dahlsten DL (2020) Mountain Chickadee (Poecile gambeli). In: Billerman SM, Keeney BK, Rodewald PG, Schulenberg TS (eds) Birds of the World. Cornell Lab of Ornithology\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMinock ME (1972) Interspecific aggression between black-capped and mountain chickadees at winter feeding stations. Condor 74:454\u0026ndash;461\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eM\u0026ouml;nkk\u0026ouml;nen M, Helle P, Soppela K (1990) Numerical and behavioural responses of migrant passerines to experimental manipulation of resident tits (Parus spp.): heterospecific attraction in northern breeding bird communites? Oecologia 85:218\u0026ndash;225\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMorse DH (1977) Feeding Behavior and Predator Avoidance in Heterospecific Groups. Bioscience 27:332\u0026ndash;339. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.2307/1297632\u003c/span\u003e\u003cspan address=\"10.2307/1297632\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMorse DH (1974) Niche breadth as a function of social dominance. Am Nat 108:818\u0026ndash;830\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eM\u0026uuml;ller CA, Manser MB (2007) Nasty neighbours\u0026rsquo; rather than \u0026lsquo;dear enemies\u0026rsquo; in a social carnivore. Proc R Soc B Biol Sci 274:959\u0026ndash;965\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNorris AR, Drever MC, Martin K (2013) Insect outbreaks increase populations and facilitate reproduction in a cavity-dependent songbird, the M ountain C hickadee P oecile gambeli. Ibis 155:165\u0026ndash;176\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNorris AR, Martin K (2010) The perils of plasticity: dual resource pulses increase facilitation but destabilize populations of small-bodied cavity-nesters. Oikos 119:1126\u0026ndash;1135\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNorris AR, Martin K (2014) Direct and indirect effects of an insect outbreak increase the reproductive output for an avian insectivore and nest-cavity excavator, the red-breasted nuthatch Sitta canadensis. J Avian Biol 45:280\u0026ndash;290\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNorris AR, Martin K (2008) Mountain pine beetle presence affects nest patch choice of red-breasted nuthatches. J Wildl Manag 72:733\u0026ndash;737\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNorris AR, Martin K (2012) Red-breasted nuthatches (Sitta canadensis) increase cavity excavation in response to a mountain pine beetle (Dendroctonus ponderosae) outbreak. Ecoscience 19:308\u0026ndash;315\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNorris AR, Martin K, Cockle KL (2022) Weather and nest cavity characteristics influence fecundity in mountain chickadees. PeerJ 10:e14327\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eOstfeld RS, Keesing F (2000) Pulsed resources and community dynamics of consumers in terrestrial ecosystems. Trends Ecol Evol 15:232\u0026ndash;237\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eOtter KA (2007) Ecology and Behavior of Chickadees and Titmice: An Integrated Approach. OUP Oxford\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePetit LJ, Petit DR (1996) Factors governing habitat selection by prothonotary warblers: field tests of the Fretwell-Lucas models. Ecol Monogr 66:367\u0026ndash;387\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eR Core Team R (2013) R: A language and environment for statistical computing\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eReid R (1962) Biology of the Mountain Pine Beetle, Dendroctonus monticolae Hopkins, in the East Kootenay Region of British Columbia I. Life Cycle, Brood Development, and Flight Periods1. Can Entomol 94:531\u0026ndash;538\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRipley B, Venables B, Bates DM et al (2013) Package \u0026lsquo;mass\u0026rsquo;. Cran R 538:113\u0026ndash;120\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRobinson PA, Norris AR, Martin K (2005) Interspecific nest sharing by Red-breasted Nuthatch and Mountain Chickadee. Wilson Bull 117:400\u0026ndash;402\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eShizuka D, Johnson AE (2020) How demographic processes shape animal social networks. Behav Ecol 31:1\u0026ndash;11. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1093/beheco/arz083\u003c/span\u003e\u003cspan address=\"10.1093/beheco/arz083\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSridhar H, Beauchamp G, Shanker K (2009) Why do birds participate in mixed-species foraging flocks? A large-scale synthesis. Anim Behav 78:337\u0026ndash;347. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.anbehav.2009.05.008\u003c/span\u003e\u003cspan address=\"10.1016/j.anbehav.2009.05.008\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSt Clair JJH, Burns ZT, Bettaney EM et al (2015) Experimental resource pulses influence social-network dynamics and the potential for information flow in tool-using crows. Nat Commun 6:7197. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1038/ncomms8197\u003c/span\u003e\u003cspan address=\"10.1038/ncomms8197\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eStamps JA (1988) Conspecific attraction and aggregation in territorial species. Am Nat 131:329\u0026ndash;347\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eStrauss ED, Shizuka D (2022) The dynamics of dominance: open questions, challenges and solutions. Philos Trans R Soc B Biol Sci 377:20200445. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1098/rstb.2020.0445\u003c/span\u003e\u003cspan address=\"10.1098/rstb.2020.0445\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTaylor SW, Carroll AL (2003) Disturbance, forest age, and mountain pine beetle outbreak dynamics in BC: A historical perspective. Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre \u0026hellip;\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTempleton CN, Greene E (2007) Nuthatches eavesdrop on variations in heterospecific chickadee mobbing alarm calls. Proc Natl Acad Sci 104:5479\u0026ndash;5482\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eThomas JW (1979) Wildlife habitats in managed forests: the Blue Mountains of Oregon and Washington. Wildlife Management Institute\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eThompson JN (1988) Variation in Interspecific Interactions. Annu Rev Ecol Syst 19:65\u0026ndash;87. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1146/annurev.es.19.110188.000433\u003c/span\u003e\u003cspan address=\"10.1146/annurev.es.19.110188.000433\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003evan der Hoek Y, Gaona GV, Ciach M, Martin K (2020) Global relationships between tree-cavity excavators and forest bird richness. R Soc Open Sci 7:192177\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWaite TA, Grubb TC (1988) Copying of Foraging Locations in Mixed-Species Flocks of Temperate-Deciduous Woodland Birds: An Experimental Study. Condor 90:132\u0026ndash;140. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.2307/1368442\u003c/span\u003e\u003cspan address=\"10.2307/1368442\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang H, Ma L, Wang J, Hou J (2022) Modulation of dear enemy effects by male dusky warblers (Phylloscopus fuscatus) at different reproductive stages. Behav Processes 200:104706. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.beproc.2022.104706\u003c/span\u003e\u003cspan address=\"10.1016/j.beproc.2022.104706\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWerba JA, Stuckert AM, Edwards M, McCoy MW (2022) Stranger danger: A meta-analysis of the dear enemy hypothesis. Behav Processes 194:104542. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.beproc.2021.104542\u003c/span\u003e\u003cspan address=\"10.1016/j.beproc.2021.104542\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWiebe KL (2003) Delayed timing as a strategy to avoid nest-site competition: testing a model using data from starlings and flickers. Oikos 100:291\u0026ndash;298\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYang LH, Bastow JL, Spence KO, Wright AN (2008) What can we learn from resource pulses. Ecology 89:621\u0026ndash;634\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYdenberg RC, Giraldeau L, Falls JB (1988) Neighbours, strangers, and the asymmetric war of attrition. Anim Behav 36:343\u0026ndash;347\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYoon J, Sillett TS, Morrison SA, Ghalambor CK (2012) Breeding density, not life history, predicts interpopulation differences in territorial aggression in a passerine bird. Anim Behav 84:515\u0026ndash;521. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.anbehav.2012.05.024\u003c/span\u003e\u003cspan address=\"10.1016/j.anbehav.2012.05.024\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"interspecific competition, dominance hierarchies, social resilience, ecological resilience, ecological disruption, behavioural interactions","lastPublishedDoi":"10.21203/rs.3.rs-4360933/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4360933/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eTo explore how social networks might respond to ecological change we investigated the impact of two natural resource pulses at the foraging and nidic levels on intra- and inter-specific territorial behaviour of two species that co-occur year-round in multi-species groups. We simulated conspecific and heterospecific territorial intrusions in two insectivorous cavity-nesting species using 974 model presentations with territorial song playbacks during and after a dual resource pulse of insect (bark beetle) prey and nest cavities across 5 years in British Columbia, Canada. As beetle abundance increased, both species increased aggression toward conspecific intruders, but at peak beetle abundance, the (typically) subordinate generalist insectivore, mountain chickadee (\u003cem\u003ePoecile gambeli\u003c/em\u003e), attacked model intruders more frequently than did the dominant bark insectivore, red-breasted nuthatch (\u003cem\u003eSitta canadensis\u003c/em\u003e). Surprisingly, chickadees shifted to an inter-specific resource defense strategy, responding more aggressively to nuthatch intruders than to conspecifics. Thus, obligate secondary cavity nesting chickadees dominated facultative excavating nuthatches, providing evidence of a dominance reversal at the nesting guild level. Both insectivores increased defense of high-quality territories, with increasing availability of food resources. The reversal in the interspecific dominance hierarchy suggests that behavioural mechanisms governing social networks and community structure may change during resource pulses. Overall, we suggest that social networks of chickadees and nuthatches are dynamic with high complexity and flexibility to major ecological disruptions. Future work that examines the fitness consequences of temporal variation in social network dynamics and resiliency could help to reveal evolutionary mechanisms by which these species co-exist.\u003c/p\u003e","manuscriptTitle":"Natural resource pulses influence social-network dynamics: experimental evidence from a tree cavity-dependent bird community","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-05-29 17:34:34","doi":"10.21203/rs.3.rs-4360933/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"d73a27de-cdd8-4082-b676-91b0c354b2cc","owner":[],"postedDate":"May 29th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-07-08T04:33:49+00:00","versionOfRecord":[],"versionCreatedAt":"2024-05-29 17:34:34","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4360933","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4360933","identity":"rs-4360933","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}