Vegetation structure shapes occupancy patterns of specialist and non-specialist birds in xerophytic woodlands

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Barzan, Noelia C. Calamari, Andrea P. Goijman, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8928094/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 Dry forests and woodlands are valuable yet fragile ecosystems prone to rapid degradation and structural simplification by overuse, including livestock grazing, fire, and logging. In these systems, forest birds depend on vegetation structural complexity to meet key foraging and breeding needs, making them sensitive indicators of habitat condition. We assessed bird occupancy in the Espinal woodlands of east-central Argentina, testing whether assemblage- and species level occupancy patterns of woodland specialists’ and non-woodland birds were related to vegetation structure and mediated by habitat affinity. Using a hierarchical occupancy model under Bayesian framework, we found that woodland specialists were associated with sites featuring closed canopies and larger trees, whereas non- woodland (disturbance-tolerant) species were more frequent open and structurally simplified woodlands. Increasing degradation—characterized by smaller trees, reduced canopy cover, and increased shrub encroachment— drove shifts from specialist-dominated assemblages toward those dominated by non-woodland (open-areas and shrubland) species. Several common woodland species showed consistent associations with well-preserved dense woodlands or with mature but more open stands, supporting their potential use as indicators of woodland condition. Although maintaining high canopy cover and large trees is essential for conserving disturbance-sensitive woodland bird assemblages, some insectivorous species restricted to xerophytic woodlands preferred mature stands with open understories, underscoring the importance of structural heterogeneity. Our results highlight the value of detectability-corrected occupancy modeling for identifying assemblage- and species-level responses to woodland degradation and for guiding conservation-oriented management in livestock-grazed dry woodlands. Terrestrial Ecology multi-species occupancy woodland specialists non-woodland species avian assemblages canopy cover tree diameter xerophytic woodlands Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 1. Introduction Dry forest and woodlands are valuable yet fragile ecosystems prone to rapid degradation and transformation by overuse, including livestock grazing, fire, and logging (Janzen 1998 ; Hoekstra et al. 2005 ; Torres et al. 2014 ; Macchi et al. 2019 ). These ecosystems harbour significant biodiversity and endemic species that contribute uniquely to global biodiversity (Ribeiro et al. 2021 ). In dry forests, transformation processes can be accelerated by wind and water erosion (Li and Jiang 2021 ) making their structural integrity essential for sustaining biological communities. Forest birds in these ecosystems are sensitive indicators of habitat quality, ecosystem functionality, and environmental degradation, as they rely on vegetation structure and composition to meet key ecological requirements such as breeding and foraging (Waltert et al. 2004 ; Prieto-Torres et al. 2018 ; Macchi et al. 2020 ; Briggs and Mainwaring 2022 ). Bird species responses to habitat degradation vary according to ecological traits. For example, ground-foraging birds are particularly affected by overgrazing, while those that feed and nest on large trees may respond negatively to forest cutting and fires in open xerophytic forests (Albanesi et al. 2014 ; Bellis et al. 2015 ; Neilly and Schwarzkopf 2019 ; Stanton et al. 2021 ; Dardanelli et al. 2022 ). Shrub encroachment -often promoted by long-term overgrazing in native forests (Asner et al. 2004 ; Sione et al. 2006 ; Stanton Jr et al. 2018 )- may benefit shrub-nesting birds but would be detrimental to cavity-nesting birds and ground-feeding birds (Barzan et al. 2023 ). Consequently, forest specialist birds then would be favored in forest with larger trees and closed canopy and decrease in degraded forest with lower canopy cover, smaller trees and denser shrub layer (Shahabuddin et al. 2021 ; Tallei et al. 2021 ; Barzan et al. 2023 ). In contrast, non-forest species tend to increase in successional forests and woodlands with open canopy and smaller trees (Albanesi et al. 2014 ; Bellis et al. 2015 ). This shift in community composition are often accompanied by changes in functional traits, with declines in insectivores and frugivorous birds and increases in granivores as degraded progresses (Gray et al. 2007 ; Albanesi et al. 2014 ). Identifying forest conditions that reconcile bird conservation with sustainable livestock production has been highlighted as a priority in grazed woodlands (Johnson et al. 2017 ; Frutos et al. 2020b , a ). In the xerophytic Espinal woodland of central-east Argentina, well preserved woodlands are preferred by local livestock farmers and conservationists over degraded ones (Rojido et al. 2021 ). The Espinal forest is a xerophytic woodland used mainly for livestock grazing by domestic cattle and sheep (Soca et al. 2020 ), and host about 30% of the total bird species in the country (Dardanelli et al. 2018 ). Previous studies in this region explored how woodland structure affected bird functional and taxonomic diversity, height-foraging guilds, and the occupancy of a few focal species (Dardanelli et al. 2022 ; Barzan et al. 2023 , 2025 , 2026 ). However, most have not accounted for imperfect detection or simultaneously evaluated community-level and all species-level responses to vegetation structure, limiting their ability to identify robust indicator species of woodland quality for birds. Occupancy models address this limitations by estimating the probability that a species occupies a site while explicitly accounting for imperfect detection and variation in sampling effort, study period, and other covariates (MacKenzie et al. 2006 ; Goijman and Zarco 2024 ). Multispecies hierarchical occupancy models further enable the simultaneous assessment of community-level and species-specific patterns, making them particularly suitable developing ecological indicators (Fraixedas et al. 2020 ). There is increasing interest in identifying birds that can be used as community and species-level indicators of forest condition, particularly those are easily recognizable, providers of key ecosystems services, abundant, and easy to capture and mark for individual tracking (Fraixedas et al. 2020 ). Therefore, analyzing the relationship between the occupancy of individual species and bird assemblages (based on their habitat affinity) would provide a broader and more precise set of detectability-corrected indicators, creating a more comprehensive toolbox for monitoring biodiversity conservation in livestock-managed xerophilous forests. We used a Bayesian framework to investigate avian site occupancy in relation to vegetation structure along a degradation gradient in Espinal woodlands. Our objectives were to (1) assess how woodland-affinity bird assemblages (forest specialists and non-forest specialists) and individual species respond to key woodland vegetation structure variables, and (2) identify potential indicator species of woodland condition in livestock managed xerophytic woodlands. We hypothesized that occupancy patterns of woodland and non-woodland birds, at both the assemblage and species level, would reflect their habitat affinities. Specifically, we predict that increasing degradation –characterized by smaller trees, lower canopy cover, and higher shrub cover- would shift bird assemblages from dominance by woodland specialists to assemblages dominated by adaptable non-woodland species, including open-area and successional shrubland birds. Furthermore, we predict that birds that provide valuable ecosystem functions, such as insectivores and frugivorous will be particularly affected by woodland degradation. Finally, we proposed a set of species useful for monitoring woodland condition and bird conservation in xerophytic woodlands under livestock grazing management. 2. Materials and methods 2.1. Study area We conducted the study in the northeast of the Espinal ecoregion, in Entre Ríos province, Argentina (Fig. 1 ). The region is characterized by the presence of thorny shrubs and trees that form xerophytic woodlands and savannas interspersed with patches of agricultural lands (Lewis et al. 2009 ; Morello et al. 2012 ). Vegetation consists of low (6 to 12 m), and semi-open xerophytic woodland, dominated by Algarrobos (Mesquite) trees, mainly Neltuma affinis and N. nigra accompanied by Vachellia caven , Celtis tala , and Geoffroea decorticans (Morello et al. 2012 ). The shrub layer commonly includes species of the genera Baccharis, Aloysia , Castella , Vernonia , and Eupatorium (Menéndez and La Rocca 2006 , 2007 ). The herbaceous stratum includes herbs and grasses, and has a high richness, with more than 200 species (Menéndez and La Rocca 2006 ). Mean annual temperatures in the study area range from 13°C to 23°C, and mean annual precipitation is approximately 1000 mm; however, a marked water deficit occurs due to high evapotranspiration and low soil infiltration associated with the clayey substrate (Menéndez and La Rocca 2006 , 2007 ). The landscape topography consist of flat plains interspersed with smooth undulations (Menéndez and La Rocca 2006 , 2007 ). Livestock grazing and crop production are the main economic activities (Morello et al. 2012 ). The size of the farms usually variates between 200 and 1000 ha. 2.2. Sampling design The study was conducted on livestock farms where grazing occurs within Espinal woodlands. Farms were primarily dedicated to extensive cattle raising, with a mix of cattle and sheep ranching to a lesser extent. Signs of environmental degradation, including bare soil and low grass height and cover, were common. We selected 30 livestock paddocks across 15 farms distributed throughout the study area (Fig. 1 ). Farm size ranged from 50.5 to 1333.5 ha (mean = 351.2 ha). We sampled in 15 closed forest paddocks (higher shrub and tree stratum cover) and 15 open forest paddocks (lower shrub and tree stratum cover). Within each paddock, a 250 × 250 m grid was overlaid on maps to identify cells containing native woodland. From these, three grid cells with closed woodlands and three with open woodlands were selected to ensure variation in woody vegetation density. One bird sampling point was established in each selected cell, spaced at least 250 m apart and ≥ 100 m from paddock edges to minimize edge effects (Ralph et al. 1993 ; Bibby et al. 2000 ; Maya-Elizarrarás and Schondube 2015 ; Dardanelli et al. 2022 ). In total, 90 bird sampling points were surveyed. Birds were surveyed during the austral spring of 2021 using fixed-radius (50 m) point counts (Bibby et al. 2000 ). Three observers (SD, CFR & AEF) with more than 15 years of experience surveying birds within the Espinal ecoregion and similar ability to detect birds undertook the bird sampling, always during favorable weather conditions (minimal wind and no rain). At each paddock, three point-counts were visited twice, each time by a different randomly assigned observer, ensuring equal sampling effort among observers. Birds were classified into two assemblages based on habitat affinity: “woodland” and “non-woodland” species. Woodland and non-woodland bird species and assemblages wee modeled separately. To assess vegetation structure, we established 30 m transects centered on each bird point-count. Measurements were taken every 3 m along each transect. Canopy cover was estimated using the “Canopy Cover” mobile application; tree diameter at breast height (DBH, cm) was estimated using a diameter tape; litter depth (cm) was estimated using a graduated ruler; and vertical vegetation structure was assessed using the point interception method (Hays et al. 1981 ). Foliage contacts on a 3.3 m graduated rod across five vertical intervals: 0–0.2 m, 0.2–0.5 m, 0.5–1 m, 1–2 m, and > 2 m. These were grouped into three strata representative of Espinal woodland: 0-0.5 m herbaceous stratum, 0.5-2 m shrub stratum, and > 2 m tree stratum. Foliage counts at each strata were counted and converted to percentage cover (Bibby et al. 2000 ). To avoid multicollinearity, correlated covariates (Pearson r > 0.6) were excluded. Foliage cover in the tree stratum (> 2 m) was removed due to its correlation with canopy cover. Additionally, herbaceous cover (0-0.5 m) and litter depth were discarded because they showed no relationship with bird occupancy, yielding poor estimates. Final occupancy models included shrub cover, diameter at breast height (DBH), and canopy cover as predictors. 2.3. Occupancy modeling To assess the influence of vegetation structure on birds, we used hierarchical multi-species occupancy models under a Bayesian framework, with points nested within paddocks (Royle and Dorazio 2008 ; Zipkin et al. 2009 ; Goijman et al. 2015 ; Goijman and Zarco 2024 ). This approach allowed us to simultaneously estimate occupancy for both the entire assemblage and individual species, while accounting for imperfect detection. We modeled detection probability using the repeated surveys per point (k = 2) as a function of the time of the day (dusk/dawn) using linear and quadratic terms, allowing for control of potential variation in bird activity during the day. Occupancy was modeled as a function of shrub cover, diameter at breast height (DBH), and canopy cover. We standardized explanatory variables (mean = 0, SD = 1). We interpreted covariate effects on occupancy based on the mean of the posterior distribution and the 95% Bayesian credible interval (95% CRI). Covariates for which CRI did not include zero were considered to have strong effects. However, for those slightly overlapping zero (i.e., f > 0.80), we also report the proportion of the posterior distribution (f) that shared the same sign as the mean. We fitted models using Markov chain Monte Carlo (MCMC) methods via the jagsUI package (Kellner 2015 ) in R version 4.2.1 (R Development Core Team. 2022). We ran three chains of 100,000 iterations each and discarded the first 10,000 as burn-in, adapting 50,000 iterations with a thinning rate of 10. We used weakly informative priors for all parameters. Model convergence was assessed via visually inspecting trace plots and by calculating the Gelman–Rubin statistic, where values below 1.1 indicated satisfactory convergence (Gelman and Rubin 1992 ). 3. Results We recorded a total of 100 bird species, 57 were woodland species and 43 non-woodland species (Table S1). 3.1. Detection probabilities Detection probabilities (p) differed with time of day. Some species wee more detectable during the morning surveys, others during the evening surveys, while several showed no clear differences, indicating the absence of a consistent temporal pattern across species (Fig. S1, Fig. S2). Among woodland species, the highest detection probabilities -above 50%- were observed for the Small-billed Elaenia ( Elaenia parvirostris ), White-tipped Dove ( Leptotila verreauxi ), Spot-winged Pigeon ( Patagioenas maculosa ), Golden-billed Saltator ( Saltator aurantiirostris ), and Creamy-bellied Thrush ( Turdus amaurochalinus ). Among non-woodland species detection probabilities exceeding 50% were recorded for the Rufous-crowned Pygmy Tyrant ( Euscarthmus meloryphus ), Chalk-browed Mockingbird ( Mimus saturninus ), Rufous-collared Sparrow ( Zonotrichia capensis ), and House-Wren ( Troglodytes aedon ). 3.2. Responses of birds’ occupancy to vegetation structure The vegetation structure variables were related to the occupancy of both woodland and non-woodland assemblages, as well as with 77 out of 100 modeled bird species (Fig. 2 , Fig. 3 ). Globally, canopy cover showed the strongest effect, positively associated with woodland assemblage occupancy and negatively with non-woodland species. DBH showed a positive influence on the woodland assemblage but showed no clear effect on the non-woodland assemblage. Shrub cover did not affect assemblage-level occupancy for either group (Fig. 2 , Fig. 3 ). At the species level, canopy cover was also the vegetation structure variable that most influenced occupancy probabilities for bird species. Positive associations with canopy cover were found for 16 woodland species, including Small-billed Elaenia parvirostris ; Pearly-vented Tody-Tyrant Hemitriccus margaritaceiventer , White-tipped Dove Leptotila verreauxi , White-winged Becard Pachyramphus polychopterus , Green-winged Saltator Saltatir similis , Tropical Parula Setophaga pitiayumi , Great Antshrike Taraba major , Rufous-bellied Thrush Turdus rufiventris , and Ultramarine Grosbeak Cyanoloxia brissonii , among others (Fig. 2 , Fig. 4 ). In contrast, negative associations with canopy cover were found for 35 non-woodland species, including Chalk-browed Mockingbird Mimus saturninus , Grassland Sparrow Ammodramus humeralis , Red-crested Cardinal Paroaria coronata , Rufous Hornero Furnarius rufus , Double-collared Seedeater Sporophila caerulescens , Saffron Finch Sicalis flaveola , among others (Fig. 3 , Fig. 5 ). Tree diameter (DBH), was positively related to the occupancy of 25 woodland species, including Sayaca tanager Thraupis sayaca , Green-winged Saltator similis , Large Elaenia spectabilis , Tropical Parula Setophaga pitiayumi ; Picazuro pigeon Patagioenas picazuro , White-fronted Woodpecker Melanerpes cactorum , Grayish saltator Saltator coerulescens , Small-billed Elaenia parvirostris , and Narrow-billed Woodcreeper Lepidocolaptes angustirostris , among others (Fig. 2 , Fig. 6 ). Among non-woodland bird species, only seven were positively related to DBH -Grayish Baywing Agelaioides badius , Picui Ground-Dove Columbina picui , Plumbeous Ibis Theristicus caerulescens , Chotoy Spinetail Schoeniophylax phryganophilus , Fork-tailed Flycatcher Tyrannus savana , Pale-breasted Spinetail Synallaxis albescens , and Eared Dove Zenaida auriculata - (Fig. 3 , Fig. 7 ). Lastly, shrub cover showed contrasting effects at the species level (Fig. 2 , Fig. 3 ). Eleven woodland species exhibited positively associated with shrub cover, including Ultramarine Grosbeak Cyanoloxia brissonii , Pearly-vented Tody-Tyrant Hemitriccus margaritaceiventer , Gilded Hummingbird Hylocharis chrysura , and Tropical Parula Setophaga pitiayumi , among others. In contrasts, eight woodland species showed negative associations with shrub cover, including the Scimitar-billed Woodcreeper Drymornis bridgesii , Suiriri flycatcher Suiriri , Swainson's Flycatcher Myiarchus swainsoni , and Brown Cacholote Pseudoseisura lophotes , among others (Fig. 8 ). Among non-woodland bird species, shrub cover was negatively associated with the occupancy of 11 species, including Saffron finch Sicalis flaveola , Rufous Hornero Furnarius rufus , Monk Parakeet Myiopsitta monachus , Grayish Baywing Agelaioides badius , and Lark-like Brushrunner Coryphistera aludina , among others. In contrast, positive associations were found in only three species: the Rufous-crowned Pygmy Tyrant Euscarthmus meloryphus , the Red-crested Finch Coryphospingus cuculatus , and the Striped Cuckoo Tapera naevia (Fig. 9 ). 4. Discussion 4.1 Vegetation structure variables and bird occupancy Woodland birds and non-woodland birds showed contrasting responses to vegetation structure in xerophytic woodlands at both the assemblage and species levels. Woodland birds were primarily associated with mature woodlands characterized by large trees and closed canopies, whereas non-woodland species were more frequent in open woodlands with a lower canopy and shrub cover. Along a degradation gradient marked by decreasing tree diameter, and canopy cover, and increased shrub encroachment, bird assemblages shifted from dominance by woodland specialists to communities dominated by non-woodland birds associated with open-areas and successional scrublands. This pattern likely reflects the tendency of open woodlands -whether naturally open or thinned by livestock grazing- to be colonized by non-woodland species, consistent with previous studies in xerophytic woodlands and dry forests (Codesido et al. 2009 ; Albanesi et al. 2014 ; Loyn and McNabb 2015 ; Hansen et al. 2019 ; Dardanelli et al. 2022 ). Canopy cover emerged as the most influential vegetation structure variable, as it was related to the occupancy of 51 bird species and both assemblages. It consistently favored woodland species and negatively affected non-woodland species at the assemblage and species levels, corroborating earlier studies (Laiolo 2004 ; Hanspach et al. 2011 ; Hansen et al. 2019 ; Dardanelli et al. 2022 ). Our study extends previous work by demonstrating simultaneous, contrasting responses across entire assemblages of woodland and non-woodland birds, as well as among numerous individual species, a feature not documented in previous studies. Tree diameter (DBH) was also a key driver for woodland birds’ occupancy, with larger trees (over ~ 20-25cm) favoring 25 woodland species, most of which nest in trees (de la Peña 2006, 2013 ). Similar dependencies on large trees have been reported in other dry forest and woodland systems (Hansen et al. 2019 ; Neilly and Schwarzkopf 2019 ; Dardanelli et al. 2022 ). Although DBH was less important for non-woodland species, some open area and shrubland bird species -like the Fork-tailed Flycatcher, Plumbeous Ibis, Picui Ground Dove, Grayish Baywing, Pale-breasted Spinetail, and Chotoy Spinetail- showed positive associations, probably reflecting nesting requirements in isolated trees (de la Peña 2006, 2013 ). Similar results were found in grasslands with isolated trees in Uruguay (Aldabe et al. 2024). In contrast to canopy cover and DBH, shrub cover had a weaker and more variable influence. While neutral at the assemblage level for both groups, species-level responses mostly negative for non-woodland birds, and mixed for woodland birds (11 positive and eight negative). The mixed effect for woodland species was also reported for dry Chaco woodlands in northern Argentina (Codesido et al. 2009 ). Overall, these results highlight the importance of maintaining mature woodland structure to preserve woodland birds -particularly high canopy cover and large trees, while recognizing that understory heterogeneity can support species with differing ecological requirements. This structural degradation may also affect ecosystem services, as many of the species sensitive to shrub encroachment are insectivores contributing to invertebrate control. By explicitly taking into account imperfect detection, the hierarchical multispecies occupancy approach used here allowed us to identify responses to forest structure at both the assemblage and species-specific levels, strengthening the interpretation of vegetation-bird occupancy relationships in managed xerophytic forests. 4.2 Potential indicator bird species of woodland functionality Building on the vegetation structure-occupancy relationships identified above, several of the 77 species with significant structural associations merge as potential candidates for indicators of woodland functionality due to their consistent responses, abundance, conspicuousness and frequent capture in regional mist nest surveys (Guidetti 2020 ; Dellafiore and Brandolin 2023 ; Berón et al. 2025 ). These traits facilitate their potential use in monitoring programs, including individual marking and long-term tracking (Gregory et al. 2003 ; Mekonen 2017 ). Three common woodland species -the Green-winged Saltator ( Saltator similis ), the Tropical Parula ( Setophaga pitiayumi ), and the Large Elaenia ( Elaenia spectabilis )- were associated with dense, well preserved woodlands characterized by closed canopies, large trees, and closed understories. These species may serve as effective indicators of dense woodland condition while also contributing key ecosystem services such as like seed dispersal and invertebrate control (Cueto and Casenave 2002 ; Hoffmann and Krügel 2007 ; Berón et al. 2025 ; Billerman et al. 2025 ). Consistent with our results, the Large Elaenia and the Tropical Parula have previously been identified as indicator of woody density in the dry Chaco woodlands (Macchi et al. 2019 ). A second group of six common species, the Small-billed Elaenia ( Elaenia parvirostris ), the Grayish Saltator ( Saltator coerulescens ), the White-rimmed Warbler ( Myiothlypis leucoblepharus ), the Narrow-billed Woodcreeper ( Lepidocolaptes angustirostris ), the Great Antshrike ( Taraba major ), and the Rufous-bellied Thrush ( Turdus rufiventris ), was associated with mature woodlands with large trees and closed canopies, but showed no response to shrub cover. These species are therefore well suited as indicators of mature xerophytic woodlands with less dense understory, and also provide important ecosystem services through seed dispersal and insect predation (Hoffmann and Krügel 2007 ; Berón et al. 2025 ; Billerman et al. 2025 ). Finally, several insectivores’ woodland species contributing to invertebrate control services -such as Suiriri , Empidonomus aurantioatrocristatus , Pseudoseisura lophotes , Asthenes baeri , and Drymornis bridgesii - were negatively associated to shrub cover. These species are characteristic of mature, semi-open woodlands central Argentina (Chaco Woodland and Espinal Woodland; Morello et al. 2012 ), and are restricted in both habitat and geographic range. Consequently, they should be prioritized in conservation planning, with management strategies aimed at maintaining open understory conditions. In contrast, woodland species positively associated with shrub cover tend to exhibit broader habitat affinities, occurring in both dry woodlands and humid forests (Nores et al. 2005 ; Brarda et al. 2024 ; Billerman et al. 2025 ) and wider distribution range (Billerman et al. 2025 ), reducing their value as indicators of specific woodland conditions due to greater ecological plasticity. 5. Conclusions Bird species and assemblages in xerophytic Espinal woodlands responded to gradients of vegetation structure associated with degradation. Woodland species were consistently favored by mature woodland conditions characterized by closed canopies and large trees; whereas non-woodland species were favored in open and structurally simplified woodlands. These contrasting responses resulted in clear shifts in community composition as vegetation structure was structurally simplified, from assemblages dominated by woodland specialists to those dominated by disturbance-tolerant non-woodland species. Canopy cover appeared as the main driver of bird occupancy at both assemblage and species levels, highlighting its fundamental part in maintaining woodland birds. Tree size reinforced the importance of mature woodland structure, especially for species that nest in trees. In contrast, shrub cover has weaker and more heterogeneous effects, reflecting different understory preferences among species. Markedly, shrub encroachment disproportionately affected insectivorous birds, suggesting potential consequences for ecosystem services like invertebrate control. Together, these findings stress that conserving bird diversity in livestock grazed xerophytic woodlands requires maintaining mature woodland structure, particularly high canopy cover and mature trees, while conserving heterogeneity in the shrub stratum. Management strategies that maintain canopy cover and avoid shrub encroachment are hence essential to preserve woodland specialists’ birds and the ecological functions they provide. The detectability-corrected, assemblage- and species level responses identified in this study offer a robust framework for monitoring woodland condition and guiding conservation-oriented grazing management in dry woodlands in central Argentina. Declarations Acknowledgments We sincerely thank private landowners who allowed us to stay and sample birds and vegetation in their properties. Funding This work was funded by Argentine Fund for Scientific and Technological Research (FONCYT, project PICT 2019 01161). Competing Interests The authors have no relevant financial or non-financial interests to disclose. Author Contributions Sebastián Dardanelli : Conceptualization, Investigation, Data curation, Methodology, Writing - original draft, Writing - review & editing. Funding acquisition, Project administration. Flavia R. Barzan : Conceptualization, Data curation, Investigation, Visualization, Writing - review & editing. Noelia C. Calamari : Conceptualization, Investigation, Methodology, Writing - review & editing. C. Fabricio Reales : Investigation, Methodology, Writing - review & editing. Antonio E. Frutos : Investigation, Methodology, Writing - review & editing. Andrea P. Goijman : Investigation, Methodology, Formal analysis, Visualization, Writing - review & editing. Sonia B. Canavelli : Conceptualization, Investigation, Writing - review & editing. Laura M. Bellis : Investigation, Writing - review & editing. Carlos I. Piña : Investigation, Writing - review & editing. Data Availability The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request. References Albanesi S, Dardanelli S, Bellis LM (2014) Effects of fire disturbance on bird communities and species of mountain Serrano forest in central Argentina. J For Res 19:105–114. https://doi.org/10.1007/s10310-012-0388-4 Asner GP, Elmore AJ, Olander LP et al (2004) Grazing systems, ecosystem responses, and global change. Annu Rev Environ Resour 29:261–299 Barzan FR, Bellis LM, Calamari NC et al (2025) Using bird foraging height guilds and species to assess forest degradation by livestock production. 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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-8928094","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":598185036,"identity":"339b0a7e-57f9-4d43-a9e1-0886aa07695b","order_by":0,"name":"Sebastián Dardanelli","email":"data:image/png;base64,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","orcid":"https://orcid.org/0000-0003-4341-3879","institution":"CONICET","correspondingAuthor":true,"prefix":"","firstName":"Sebastián","middleName":"","lastName":"Dardanelli","suffix":""},{"id":598185037,"identity":"69921773-2887-4614-9c25-201cbc461998","order_by":1,"name":"Flavia R. 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Beta posterior mean (black dots for individual species) indicates how variation in the respective covariate influences bird occupancy. Individual species’ Bayesian credible intervals (95% CRI) colored in black do not overlap or slightly overlap zero (f-values \u0026gt;0.80, proportion of the posterior distribution had the same sign as the mean). Vertical grey lines indicate the posterior mean of beta (solid line) for the woodland species assemblage and the 95% CRI (dashed lines). Bird species codes in Table S1.\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-8928094/v1/4e73bdf7f943cade7f1d5595.png"},{"id":104399867,"identity":"85cd04b3-372b-4a92-bb4a-b063e847e50c","added_by":"auto","created_at":"2026-03-11 12:07:53","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1370874,"visible":true,"origin":"","legend":"\u003cp\u003eStandardized effects of shrub cover, DBH, and canopy cover on non-woodland species occupancy in xerophytic woodlands in central-east Argentina. Beta posterior mean (black dots for individual species) indicates how variation in the respective covariate influences bird occupancy. Individual species’ Bayesian credible intervals (95% CRI) colored in black do not overlap or slightly overlap zero (f-values \u0026gt;0.80, proportion of the posterior distribution had the same sign as the mean). Vertical grey lines indicate the posterior mean of beta (solid line) for the non-woodland species assemblage and the 95% CRI (dashed lines). Bird species codes in Table S1.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-8928094/v1/88500ed7366f9c9f3db0629c.png"},{"id":104399562,"identity":"3529ab2a-51c3-4c5d-b3ac-5c47b1674806","added_by":"auto","created_at":"2026-03-11 12:06:38","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1244394,"visible":true,"origin":"","legend":"\u003cp\u003eWoodland bird species (color lines) and woodland bird specialists’ assemblage (black line) probabilities of occupancy responses (psi + 95% CRI) to canopy cover woodlands in Argentina. Bird species codes in Table S1.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-8928094/v1/2eff47ee498234c3a5a1b662.png"},{"id":104399851,"identity":"e208d00a-4624-48af-9985-db1958e00e0c","added_by":"auto","created_at":"2026-03-11 12:07:51","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":2320047,"visible":true,"origin":"","legend":"\u003cp\u003eNon-woodland bird species (color lines) and non-woodland bird assemblage (black line) probabilities of occupancy responses (psi + 95% CRI) to canopy cover woodlands in Argentina.\u003cem\u003e \u003c/em\u003eBird species codes in Table S1.\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-8928094/v1/a901f54f81bcb5b207305e02.png"},{"id":104400208,"identity":"707cf2a4-8b93-4b92-8b3f-14ebfb8a10cc","added_by":"auto","created_at":"2026-03-11 12:09:13","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1980824,"visible":true,"origin":"","legend":"\u003cp\u003eWoodland bird species (colored line) and woodland bird specialists’ assemblage (black line) probabilities of occupancy responses (psi + 95% CRI) to DBH in woodlands in Argentina. Bird species codes in Table S1.\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-8928094/v1/e22409eb147fe13c6020ecae.png"},{"id":104399779,"identity":"df65127b-8f46-4596-b106-fd5c0223fec8","added_by":"auto","created_at":"2026-03-11 12:07:34","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":533398,"visible":true,"origin":"","legend":"\u003cp\u003eNon-woodland bird species’ (colored line) and non-woodland bird assemblage (black line) probability of occupancy responses (psi + 95% CRI) to DBH in woodlands in Argentina. Bird species codes in Table S1.\u003c/p\u003e","description":"","filename":"image7.png","url":"https://assets-eu.researchsquare.com/files/rs-8928094/v1/8af6d35d3f4d968665b7d81d.png"},{"id":104399969,"identity":"6d188f5a-6f35-4a99-83c7-6eb15299767a","added_by":"auto","created_at":"2026-03-11 12:08:20","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":1493344,"visible":true,"origin":"","legend":"\u003cp\u003eWoodland bird species (color lines) and woodland bird specialists’ assemblage (black lines) probabilities of occupancy responses (psi + 95% CRI) to shrub cover in woodlands in Argentina. Bird species codes in Table S1.\u003c/p\u003e","description":"","filename":"image8.png","url":"https://assets-eu.researchsquare.com/files/rs-8928094/v1/51673ad658e2a390279ce255.png"},{"id":104400341,"identity":"8508e68b-91db-409d-98b7-36d2fe8663ca","added_by":"auto","created_at":"2026-03-11 12:09:41","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":1128668,"visible":true,"origin":"","legend":"\u003cp\u003eNon-woodland bird species (color lines) and non-woodland bird assemblage (black lines) probabilities of occupancy responses (psi + 95% CRI) to shrub cover in woodlands in Argentina Bird species codes in Table S1.\u003c/p\u003e","description":"","filename":"image9.png","url":"https://assets-eu.researchsquare.com/files/rs-8928094/v1/b30be9af689735b5f6943836.png"},{"id":104410520,"identity":"35964a2f-5f4d-44fd-8211-ba49e84cd52a","added_by":"auto","created_at":"2026-03-11 12:52:33","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":11658751,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8928094/v1/1157a482-d68a-421a-a588-3fe8c1b5fd2a.pdf"},{"id":103711224,"identity":"8810abea-4686-4561-b1bb-55497f79dc98","added_by":"auto","created_at":"2026-03-02 03:45:15","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":983722,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eElectronic Supplementary Material\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"Supplementarymaterial2.docx","url":"https://assets-eu.researchsquare.com/files/rs-8928094/v1/4e6841ba9bf6ba2958ff9987.docx"}],"financialInterests":"The authors declare no competing interests.","formattedTitle":"\u003cp\u003eVegetation structure shapes occupancy patterns of specialist and non-specialist birds in xerophytic woodlands\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eDry forest and woodlands are valuable yet fragile ecosystems prone to rapid degradation and transformation by overuse, including livestock grazing, fire, and logging (Janzen \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e1998\u003c/span\u003e; Hoekstra et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Torres et al. \u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Macchi et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). These ecosystems harbour significant biodiversity and endemic species that contribute uniquely to global biodiversity (Ribeiro et al. \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). In dry forests, transformation processes can be accelerated by wind and water erosion (Li and Jiang \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) making their structural integrity essential for sustaining biological communities.\u003c/p\u003e \u003cp\u003eForest birds in these ecosystems are sensitive indicators of habitat quality, ecosystem functionality, and environmental degradation, as they rely on vegetation structure and composition to meet key ecological requirements such as breeding and foraging (Waltert et al. \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Prieto-Torres et al. \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Macchi et al. \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Briggs and Mainwaring \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Bird species responses to habitat degradation vary according to ecological traits. For example, ground-foraging birds are particularly affected by overgrazing, while those that feed and nest on large trees may respond negatively to forest cutting and fires in open xerophytic forests (Albanesi et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Bellis et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Neilly and Schwarzkopf \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Stanton et al. \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Dardanelli et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Shrub encroachment -often promoted by long-term overgrazing in native forests (Asner et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Sione et al. \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Stanton Jr et al. \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2018\u003c/span\u003e)- may benefit shrub-nesting birds but would be detrimental to cavity-nesting birds and ground-feeding birds (Barzan et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Consequently, forest specialist birds then would be favored in forest with larger trees and closed canopy and decrease in degraded forest with lower canopy cover, smaller trees and denser shrub layer (Shahabuddin et al. \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Tallei et al. \u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Barzan et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). In contrast, non-forest species tend to increase in successional forests and woodlands with open canopy and smaller trees (Albanesi et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Bellis et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). This shift in community composition are often accompanied by changes in functional traits, with declines in insectivores and frugivorous birds and increases in granivores as degraded progresses (Gray et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Albanesi et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIdentifying forest conditions that reconcile bird conservation with sustainable livestock production has been highlighted as a priority in grazed woodlands (Johnson et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Frutos et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2020b\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003ea\u003c/span\u003e). In the xerophytic Espinal woodland of central-east Argentina, well preserved woodlands are preferred by local livestock farmers and conservationists over degraded ones (Rojido et al. \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe Espinal forest is a xerophytic woodland used mainly for livestock grazing by domestic cattle and sheep (Soca et al. \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2020\u003c/span\u003e), and host about 30% of the total bird species in the country (Dardanelli et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Previous studies in this region explored how woodland structure affected bird functional and taxonomic diversity, height-foraging guilds, and the occupancy of a few focal species (Dardanelli et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Barzan et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2023\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2025\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2026\u003c/span\u003e). However, most have not accounted for imperfect detection or simultaneously evaluated community-level and all species-level responses to vegetation structure, limiting their ability to identify robust indicator species of woodland quality for birds.\u003c/p\u003e \u003cp\u003eOccupancy models address this limitations by estimating the probability that a species occupies a site while explicitly accounting for imperfect detection and variation in sampling effort, study period, and other covariates (MacKenzie et al. \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Goijman and Zarco \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Multispecies hierarchical occupancy models further enable the simultaneous assessment of community-level and species-specific patterns, making them particularly suitable developing ecological indicators (Fraixedas et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). There is increasing interest in identifying birds that can be used as community and species-level indicators of forest condition, particularly those are easily recognizable, providers of key ecosystems services, abundant, and easy to capture and mark for individual tracking (Fraixedas et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Therefore, analyzing the relationship between the occupancy of individual species and bird assemblages (based on their habitat affinity) would provide a broader and more precise set of detectability-corrected indicators, creating a more comprehensive toolbox for monitoring biodiversity conservation in livestock-managed xerophilous forests.\u003c/p\u003e \u003cp\u003eWe used a Bayesian framework to investigate avian site occupancy in relation to vegetation structure along a degradation gradient in Espinal woodlands. Our objectives were to (1) assess how woodland-affinity bird assemblages (forest specialists and non-forest specialists) and individual species respond to key woodland vegetation structure variables, and (2) identify potential indicator species of woodland condition in livestock managed xerophytic woodlands. We hypothesized that occupancy patterns of woodland and non-woodland birds, at both the assemblage and species level, would reflect their habitat affinities. Specifically, we predict that increasing degradation \u0026ndash;characterized by smaller trees, lower canopy cover, and higher shrub cover- would shift bird assemblages from dominance by woodland specialists to assemblages dominated by adaptable non-woodland species, including open-area and successional shrubland birds. Furthermore, we predict that birds that provide valuable ecosystem functions, such as insectivores and frugivorous will be particularly affected by woodland degradation. Finally, we proposed a set of species useful for monitoring woodland condition and bird conservation in xerophytic woodlands under livestock grazing management.\u003c/p\u003e"},{"header":"2. Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Study area\u003c/h2\u003e \u003cp\u003eWe conducted the study in the northeast of the Espinal ecoregion, in Entre R\u0026iacute;os province, Argentina (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The region is characterized by the presence of thorny shrubs and trees that form xerophytic woodlands and savannas interspersed with patches of agricultural lands (Lewis et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Morello et al. \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Vegetation consists of low (6 to 12 m), and semi-open xerophytic woodland, dominated by Algarrobos (Mesquite) trees, mainly \u003cem\u003eNeltuma affinis\u003c/em\u003e and \u003cem\u003eN. nigra\u003c/em\u003e accompanied by \u003cem\u003eVachellia caven\u003c/em\u003e, \u003cem\u003eCeltis tala\u003c/em\u003e, and \u003cem\u003eGeoffroea decorticans\u003c/em\u003e (Morello et al. \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). The shrub layer commonly includes species of the genera \u003cem\u003eBaccharis, Aloysia\u003c/em\u003e, \u003cem\u003eCastella\u003c/em\u003e, \u003cem\u003eVernonia\u003c/em\u003e, \u003cem\u003eand Eupatorium\u003c/em\u003e (Men\u0026eacute;ndez and La Rocca \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2006\u003c/span\u003e, \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). The herbaceous stratum includes herbs and grasses, and has a high richness, with more than 200 species (Men\u0026eacute;ndez and La Rocca \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2006\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eMean annual temperatures in the study area range from 13\u0026deg;C to 23\u0026deg;C, and mean annual precipitation is approximately 1000 mm; however, a marked water deficit occurs due to high evapotranspiration and low soil infiltration associated with the clayey substrate (Men\u0026eacute;ndez and La Rocca \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2006\u003c/span\u003e, \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). The landscape topography consist of flat plains interspersed with smooth undulations (Men\u0026eacute;ndez and La Rocca \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2006\u003c/span\u003e, \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). Livestock grazing and crop production are the main economic activities (Morello et al. \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). The size of the farms usually variates between 200 and 1000 ha.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Sampling design\u003c/h2\u003e \u003cp\u003eThe study was conducted on livestock farms where grazing occurs within Espinal woodlands. Farms were primarily dedicated to extensive cattle raising, with a mix of cattle and sheep ranching to a lesser extent. Signs of environmental degradation, including bare soil and low grass height and cover, were common.\u003c/p\u003e \u003cp\u003eWe selected 30 livestock paddocks across 15 farms distributed throughout the study area (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Farm size ranged from 50.5 to 1333.5 ha (mean\u0026thinsp;=\u0026thinsp;351.2 ha). We sampled in 15 closed forest paddocks (higher shrub and tree stratum cover) and 15 open forest paddocks (lower shrub and tree stratum cover). Within each paddock, a 250 \u0026times; 250 m grid was overlaid on maps to identify cells containing native woodland. From these, three grid cells with closed woodlands and three with open woodlands were selected to ensure variation in woody vegetation density. One bird sampling point was established in each selected cell, spaced at least 250 m apart and \u0026ge;\u0026thinsp;100 m from paddock edges to minimize edge effects (Ralph et al. \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e1993\u003c/span\u003e; Bibby et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Maya-Elizarrar\u0026aacute;s and Schondube \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Dardanelli et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). In total, 90 bird sampling points were surveyed.\u003c/p\u003e \u003cp\u003eBirds were surveyed during the austral spring of 2021 using fixed-radius (50 m) point counts (Bibby et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2000\u003c/span\u003e). Three observers (SD, CFR \u0026amp; AEF) with more than 15 years of experience surveying birds within the Espinal ecoregion and similar ability to detect birds undertook the bird sampling, always during favorable weather conditions (minimal wind and no rain). At each paddock, three point-counts were visited twice, each time by a different randomly assigned observer, ensuring equal sampling effort among observers.\u003c/p\u003e \u003cp\u003eBirds were classified into two assemblages based on habitat affinity: \u0026ldquo;woodland\u0026rdquo; and \u0026ldquo;non-woodland\u0026rdquo; species. Woodland and non-woodland bird species and assemblages wee modeled separately.\u003c/p\u003e \u003cp\u003eTo assess vegetation structure, we established 30 m transects centered on each bird point-count. Measurements were taken every 3 m along each transect. Canopy cover was estimated using the \u0026ldquo;Canopy Cover\u0026rdquo; mobile application; tree diameter at breast height (DBH, cm) was estimated using a diameter tape; litter depth (cm) was estimated using a graduated ruler; and vertical vegetation structure was assessed using the point interception method (Hays et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e1981\u003c/span\u003e). Foliage contacts on a 3.3 m graduated rod across five vertical intervals: 0\u0026ndash;0.2 m, 0.2\u0026ndash;0.5 m, 0.5\u0026ndash;1 m, 1\u0026ndash;2 m, and \u0026gt;\u0026thinsp;2 m. These were grouped into three strata representative of Espinal woodland: 0-0.5 m herbaceous stratum, 0.5-2 m shrub stratum, and \u0026gt;\u0026thinsp;2 m tree stratum. Foliage counts at each strata were counted and converted to percentage cover (Bibby et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2000\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eTo avoid multicollinearity, correlated covariates (Pearson r\u0026thinsp;\u0026gt;\u0026thinsp;0.6) were excluded. Foliage cover in the tree stratum (\u0026gt;\u0026thinsp;2 m) was removed due to its correlation with canopy cover. Additionally, herbaceous cover (0-0.5 m) and litter depth were discarded because they showed no relationship with bird occupancy, yielding poor estimates. Final occupancy models included shrub cover, diameter at breast height (DBH), and canopy cover as predictors.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Occupancy modeling\u003c/h2\u003e \u003cp\u003eTo assess the influence of vegetation structure on birds, we used hierarchical multi-species occupancy models under a Bayesian framework, with points nested within paddocks (Royle and Dorazio \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Zipkin et al. \u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Goijman et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Goijman and Zarco \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). This approach allowed us to simultaneously estimate occupancy for both the entire assemblage and individual species, while accounting for imperfect detection.\u003c/p\u003e \u003cp\u003eWe modeled detection probability using the repeated surveys per point (k\u0026thinsp;=\u0026thinsp;2) as a function of the time of the day (dusk/dawn) using linear and quadratic terms, allowing for control of potential variation in bird activity during the day. Occupancy was modeled as a function of shrub cover, diameter at breast height (DBH), and canopy cover. We standardized explanatory variables (mean\u0026thinsp;=\u0026thinsp;0, SD\u0026thinsp;=\u0026thinsp;1).\u003c/p\u003e \u003cp\u003eWe interpreted covariate effects on occupancy based on the mean of the posterior distribution and the 95% Bayesian credible interval (95% CRI). Covariates for which CRI did not include zero were considered to have strong effects. However, for those slightly overlapping zero (i.e., f\u0026thinsp;\u0026gt;\u0026thinsp;0.80), we also report the proportion of the posterior distribution (f) that shared the same sign as the mean.\u003c/p\u003e \u003cp\u003eWe fitted models using Markov chain Monte Carlo (MCMC) methods via the jagsUI package (Kellner \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) in R version 4.2.1 (R Development Core Team. 2022). We ran three chains of 100,000 iterations each and discarded the first 10,000 as burn-in, adapting 50,000 iterations with a thinning rate of 10. We used weakly informative priors for all parameters. Model convergence was assessed via visually inspecting trace plots and by calculating the Gelman\u0026ndash;Rubin statistic, where values below 1.1 indicated satisfactory convergence (Gelman and Rubin \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e1992\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results","content":"\u003cp\u003eWe recorded a total of 100 bird species, 57 were woodland species and 43 non-woodland species (Table S1).\u003c/p\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Detection probabilities\u003c/h2\u003e \u003cp\u003eDetection probabilities (p) differed with time of day. Some species wee more detectable during the morning surveys, others during the evening surveys, while several showed no clear differences, indicating the absence of a consistent temporal pattern across species (Fig. S1, Fig. S2).\u003c/p\u003e \u003cp\u003eAmong woodland species, the highest detection probabilities -above 50%- were observed for the Small-billed Elaenia (\u003cem\u003eElaenia parvirostris\u003c/em\u003e), White-tipped Dove (\u003cem\u003eLeptotila verreauxi\u003c/em\u003e), Spot-winged Pigeon (\u003cem\u003ePatagioenas maculosa\u003c/em\u003e), Golden-billed Saltator (\u003cem\u003eSaltator aurantiirostris\u003c/em\u003e), and Creamy-bellied Thrush (\u003cem\u003eTurdus amaurochalinus\u003c/em\u003e). Among non-woodland species detection probabilities exceeding 50% were recorded for the Rufous-crowned Pygmy Tyrant (\u003cem\u003eEuscarthmus meloryphus\u003c/em\u003e), Chalk-browed Mockingbird (\u003cem\u003eMimus saturninus\u003c/em\u003e), Rufous-collared Sparrow (\u003cem\u003eZonotrichia capensis\u003c/em\u003e), and House-Wren (\u003cem\u003eTroglodytes aedon\u003c/em\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Responses of birds\u0026rsquo; occupancy to vegetation structure\u003c/h2\u003e \u003cp\u003eThe vegetation structure variables were related to the occupancy of both woodland and non-woodland assemblages, as well as with 77 out of 100 modeled bird species (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Globally, canopy cover showed the strongest effect, positively associated with woodland assemblage occupancy and negatively with non-woodland species. DBH showed a positive influence on the woodland assemblage but showed no clear effect on the non-woodland assemblage. Shrub cover did not affect assemblage-level occupancy for either group (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAt the species level, canopy cover was also the vegetation structure variable that most influenced occupancy probabilities for bird species. Positive associations with canopy cover were found for 16 woodland species, including Small-billed Elaenia \u003cem\u003eparvirostris\u003c/em\u003e; Pearly-vented Tody-Tyrant \u003cem\u003eHemitriccus margaritaceiventer\u003c/em\u003e, White-tipped Dove \u003cem\u003eLeptotila verreauxi\u003c/em\u003e, White-winged Becard \u003cem\u003ePachyramphus polychopterus\u003c/em\u003e, Green-winged Saltator \u003cem\u003eSaltatir similis\u003c/em\u003e, Tropical Parula \u003cem\u003eSetophaga pitiayumi\u003c/em\u003e, Great Antshrike \u003cem\u003eTaraba major\u003c/em\u003e, Rufous-bellied Thrush \u003cem\u003eTurdus rufiventris\u003c/em\u003e, and Ultramarine Grosbeak \u003cem\u003eCyanoloxia brissonii\u003c/em\u003e, among others (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn contrast, negative associations with canopy cover were found for 35 non-woodland species, including Chalk-browed Mockingbird \u003cem\u003eMimus saturninus\u003c/em\u003e, Grassland Sparrow \u003cem\u003eAmmodramus humeralis\u003c/em\u003e, Red-crested Cardinal \u003cem\u003eParoaria coronata\u003c/em\u003e, Rufous Hornero \u003cem\u003eFurnarius rufus\u003c/em\u003e, Double-collared Seedeater \u003cem\u003eSporophila caerulescens\u003c/em\u003e, Saffron Finch \u003cem\u003eSicalis flaveola\u003c/em\u003e, among others (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTree diameter (DBH), was positively related to the occupancy of 25 woodland species, including Sayaca tanager \u003cem\u003eThraupis sayaca\u003c/em\u003e, Green-winged Saltator \u003cem\u003esimilis\u003c/em\u003e, Large Elaenia \u003cem\u003espectabilis\u003c/em\u003e, Tropical Parula \u003cem\u003eSetophaga pitiayumi\u003c/em\u003e; Picazuro pigeon \u003cem\u003ePatagioenas picazuro\u003c/em\u003e, White-fronted Woodpecker \u003cem\u003eMelanerpes cactorum\u003c/em\u003e, Grayish saltator \u003cem\u003eSaltator coerulescens\u003c/em\u003e, Small-billed Elaenia \u003cem\u003eparvirostris\u003c/em\u003e, and Narrow-billed Woodcreeper \u003cem\u003eLepidocolaptes angustirostris\u003c/em\u003e, among others (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAmong non-woodland bird species, only seven were positively related to DBH -Grayish Baywing \u003cem\u003eAgelaioides badius\u003c/em\u003e, Picui Ground-Dove \u003cem\u003eColumbina picui\u003c/em\u003e, Plumbeous Ibis \u003cem\u003eTheristicus caerulescens\u003c/em\u003e, Chotoy Spinetail \u003cem\u003eSchoeniophylax phryganophilus\u003c/em\u003e, Fork-tailed Flycatcher \u003cem\u003eTyrannus savana\u003c/em\u003e, Pale-breasted Spinetail \u003cem\u003eSynallaxis albescens\u003c/em\u003e, and Eared Dove \u003cem\u003eZenaida auriculata\u003c/em\u003e- (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eLastly, shrub cover showed contrasting effects at the species level (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Eleven woodland species exhibited positively associated with shrub cover, including Ultramarine Grosbeak \u003cem\u003eCyanoloxia brissonii\u003c/em\u003e, Pearly-vented Tody-Tyrant \u003cem\u003eHemitriccus margaritaceiventer\u003c/em\u003e, Gilded Hummingbird \u003cem\u003eHylocharis chrysura\u003c/em\u003e, and Tropical Parula \u003cem\u003eSetophaga pitiayumi\u003c/em\u003e, among others. In contrasts, eight woodland species showed negative associations with shrub cover, including the Scimitar-billed Woodcreeper \u003cem\u003eDrymornis bridgesii\u003c/em\u003e, Suiriri flycatcher \u003cem\u003eSuiriri\u003c/em\u003e, Swainson's Flycatcher \u003cem\u003eMyiarchus swainsoni\u003c/em\u003e, and Brown Cacholote \u003cem\u003ePseudoseisura lophotes\u003c/em\u003e, among others (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAmong non-woodland bird species, shrub cover was negatively associated with the occupancy of 11 species, including Saffron finch \u003cem\u003eSicalis flaveola\u003c/em\u003e, Rufous Hornero \u003cem\u003eFurnarius rufus\u003c/em\u003e, Monk Parakeet \u003cem\u003eMyiopsitta monachus\u003c/em\u003e, Grayish Baywing \u003cem\u003eAgelaioides badius\u003c/em\u003e, and Lark-like Brushrunner \u003cem\u003eCoryphistera aludina\u003c/em\u003e, among others. In contrast, positive associations were found in only three species: the Rufous-crowned Pygmy Tyrant \u003cem\u003eEuscarthmus meloryphus\u003c/em\u003e, the Red-crested Finch \u003cem\u003eCoryphospingus cuculatus\u003c/em\u003e, and the Striped Cuckoo \u003cem\u003eTapera naevia\u003c/em\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e4.1 Vegetation structure variables and bird occupancy\u003c/h2\u003e \u003cp\u003eWoodland birds and non-woodland birds showed contrasting responses to vegetation structure in xerophytic woodlands at both the assemblage and species levels. Woodland birds were primarily associated with mature woodlands characterized by large trees and closed canopies, whereas non-woodland species were more frequent in open woodlands with a lower canopy and shrub cover. Along a degradation gradient marked by decreasing tree diameter, and canopy cover, and increased shrub encroachment, bird assemblages shifted from dominance by woodland specialists to communities dominated by non-woodland birds associated with open-areas and successional scrublands. This pattern likely reflects the tendency of open woodlands -whether naturally open or thinned by livestock grazing- to be colonized by non-woodland species, consistent with previous studies in xerophytic woodlands and dry forests (Codesido et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Albanesi et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Loyn and McNabb \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Hansen et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Dardanelli et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eCanopy cover emerged as the most influential vegetation structure variable, as it was related to the occupancy of 51 bird species and both assemblages. It consistently favored woodland species and negatively affected non-woodland species at the assemblage and species levels, corroborating earlier studies (Laiolo \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Hanspach et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Hansen et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Dardanelli et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Our study extends previous work by demonstrating simultaneous, contrasting responses across entire assemblages of woodland and non-woodland birds, as well as among numerous individual species, a feature not documented in previous studies.\u003c/p\u003e \u003cp\u003eTree diameter (DBH) was also a key driver for woodland birds\u0026rsquo; occupancy, with larger trees (over ~\u0026thinsp;20-25cm) favoring 25 woodland species, most of which nest in trees (de la Pe\u0026ntilde;a 2006, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Similar dependencies on large trees have been reported in other dry forest and woodland systems (Hansen et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Neilly and Schwarzkopf \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Dardanelli et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Although DBH was less important for non-woodland species, some open area and shrubland bird species -like the Fork-tailed Flycatcher, Plumbeous Ibis, Picui Ground Dove, Grayish Baywing, Pale-breasted Spinetail, and Chotoy Spinetail- showed positive associations, probably reflecting nesting requirements in isolated trees (de la Pe\u0026ntilde;a 2006, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Similar results were found in grasslands with isolated trees in Uruguay (Aldabe et al. 2024).\u003c/p\u003e \u003cp\u003eIn contrast to canopy cover and DBH, shrub cover had a weaker and more variable influence. While neutral at the assemblage level for both groups, species-level responses mostly negative for non-woodland birds, and mixed for woodland birds (11 positive and eight negative). The mixed effect for woodland species was also reported for dry Chaco woodlands in northern Argentina (Codesido et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2009\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eOverall, these results highlight the importance of maintaining mature woodland structure to preserve woodland birds -particularly high canopy cover and large trees, while recognizing that understory heterogeneity can support species with differing ecological requirements. This structural degradation may also affect ecosystem services, as many of the species sensitive to shrub encroachment are insectivores contributing to invertebrate control. By explicitly taking into account imperfect detection, the hierarchical multispecies occupancy approach used here allowed us to identify responses to forest structure at both the assemblage and species-specific levels, strengthening the interpretation of vegetation-bird occupancy relationships in managed xerophytic forests.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e\u003cem\u003e4.2 Potential indicator bird species of woodland functionality\u003c/em\u003e\u003c/h2\u003e \u003cp\u003eBuilding on the vegetation structure-occupancy relationships identified above, several of the 77 species with significant structural associations merge as potential candidates for indicators of woodland functionality due to their consistent responses, abundance, conspicuousness and frequent capture in regional mist nest surveys (Guidetti \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Dellafiore and Brandolin \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Ber\u0026oacute;n et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). These traits facilitate their potential use in monitoring programs, including individual marking and long-term tracking (Gregory et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; Mekonen \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2017\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThree common woodland species -the Green-winged Saltator (\u003cem\u003eSaltator similis\u003c/em\u003e), the Tropical Parula (\u003cem\u003eSetophaga pitiayumi\u003c/em\u003e), and the Large Elaenia (\u003cem\u003eElaenia spectabilis\u003c/em\u003e)- were associated with dense, well preserved woodlands characterized by closed canopies, large trees, and closed understories. These species may serve as effective indicators of dense woodland condition while also contributing key ecosystem services such as like seed dispersal and invertebrate control (Cueto and Casenave \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; Hoffmann and Kr\u0026uuml;gel \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Ber\u0026oacute;n et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2025\u003c/span\u003e; Billerman et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). Consistent with our results, the Large Elaenia and the Tropical Parula have previously been identified as indicator of woody density in the dry Chaco woodlands (Macchi et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eA second group of six common species, the Small-billed Elaenia (\u003cem\u003eElaenia parvirostris\u003c/em\u003e), the Grayish Saltator (\u003cem\u003eSaltator coerulescens\u003c/em\u003e), the White-rimmed Warbler (\u003cem\u003eMyiothlypis leucoblepharus\u003c/em\u003e), the Narrow-billed Woodcreeper (\u003cem\u003eLepidocolaptes angustirostris\u003c/em\u003e), the Great Antshrike (\u003cem\u003eTaraba major\u003c/em\u003e), and the Rufous-bellied Thrush (\u003cem\u003eTurdus rufiventris\u003c/em\u003e), was associated with mature woodlands with large trees and closed canopies, but showed no response to shrub cover. These species are therefore well suited as indicators of mature xerophytic woodlands with less dense understory, and also provide important ecosystem services through seed dispersal and insect predation (Hoffmann and Kr\u0026uuml;gel \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Ber\u0026oacute;n et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2025\u003c/span\u003e; Billerman et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2025\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eFinally, several insectivores\u0026rsquo; woodland species contributing to invertebrate control services -such as \u003cem\u003eSuiriri\u003c/em\u003e, \u003cem\u003eEmpidonomus aurantioatrocristatus\u003c/em\u003e, \u003cem\u003ePseudoseisura lophotes\u003c/em\u003e, \u003cem\u003eAsthenes baeri\u003c/em\u003e, and \u003cem\u003eDrymornis bridgesii\u003c/em\u003e- were negatively associated to shrub cover. These species are characteristic of mature, semi-open woodlands central Argentina (Chaco Woodland and Espinal Woodland; Morello et al. \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2012\u003c/span\u003e), and are restricted in both habitat and geographic range. Consequently, they should be prioritized in conservation planning, with management strategies aimed at maintaining open understory conditions. In contrast, woodland species positively associated with shrub cover tend to exhibit broader habitat affinities, occurring in both dry woodlands and humid forests (Nores et al. \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Brarda et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Billerman et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2025\u003c/span\u003e) and wider distribution range (Billerman et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2025\u003c/span\u003e), reducing their value as indicators of specific woodland conditions due to greater ecological plasticity.\u003c/p\u003e \u003c/div\u003e"},{"header":"5. Conclusions","content":"\u003cp\u003eBird species and assemblages in xerophytic Espinal woodlands responded to gradients of vegetation structure associated with degradation. Woodland species were consistently favored by mature woodland conditions characterized by closed canopies and large trees; whereas non-woodland species were favored in open and structurally simplified woodlands. These contrasting responses resulted in clear shifts in community composition as vegetation structure was structurally simplified, from assemblages dominated by woodland specialists to those dominated by disturbance-tolerant non-woodland species.\u003c/p\u003e \u003cp\u003eCanopy cover appeared as the main driver of bird occupancy at both assemblage and species levels, highlighting its fundamental part in maintaining woodland birds. Tree size reinforced the importance of mature woodland structure, especially for species that nest in trees. In contrast, shrub cover has weaker and more heterogeneous effects, reflecting different understory preferences among species. Markedly, shrub encroachment disproportionately affected insectivorous birds, suggesting potential consequences for ecosystem services like invertebrate control.\u003c/p\u003e \u003cp\u003eTogether, these findings stress that conserving bird diversity in livestock grazed xerophytic woodlands requires maintaining mature woodland structure, particularly high canopy cover and mature trees, while conserving heterogeneity in the shrub stratum. Management strategies that maintain canopy cover and avoid shrub encroachment are hence essential to preserve woodland specialists\u0026rsquo; birds and the ecological functions they provide. The detectability-corrected, assemblage- and species level responses identified in this study offer a robust framework for monitoring woodland condition and guiding conservation-oriented grazing management in dry woodlands in central Argentina.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe sincerely thank private landowners who allowed us to stay and sample birds and vegetation in their properties.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was funded by Argentine Fund for Scientific and Technological Research (FONCYT, project PICT 2019 01161).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors have no relevant financial or non-financial interests to disclose.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSebasti\u0026aacute;n Dardanelli\u003c/strong\u003e: Conceptualization, Investigation, Data curation, Methodology, Writing - original draft, Writing - review \u0026amp; editing. Funding acquisition, Project administration. \u003cstrong\u003eFlavia R. Barzan\u003c/strong\u003e: Conceptualization, Data curation, Investigation, Visualization, Writing - review \u0026amp; editing. \u003cstrong\u003eNoelia C. Calamari\u003c/strong\u003e: Conceptualization, Investigation, Methodology, Writing - review \u0026amp; editing. \u003cstrong\u003eC. Fabricio Reales\u003c/strong\u003e: Investigation, Methodology, Writing - review \u0026amp; editing. \u003cstrong\u003eAntonio E. Frutos\u003c/strong\u003e: Investigation, Methodology, Writing - review \u0026amp; editing. \u003cstrong\u003eAndrea P. Goijman\u003c/strong\u003e: Investigation, Methodology, Formal analysis, Visualization, Writing - review \u0026amp; editing. \u003cstrong\u003eSonia B. Canavelli\u003c/strong\u003e: Conceptualization, Investigation, Writing - review \u0026amp; editing. \u003cstrong\u003eLaura M. Bellis\u003c/strong\u003e: Investigation, Writing - review \u0026amp; editing. \u003cstrong\u003eCarlos I. Pi\u0026ntilde;a\u003c/strong\u003e: Investigation, Writing - review \u0026amp; editing.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAlbanesi S, Dardanelli S, Bellis LM (2014) Effects of fire disturbance on bird communities and species of mountain Serrano forest in central Argentina. 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J Appl Ecol 46:815\u0026ndash;822. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1111/j.1365-2664.2009.01664.x\u003c/span\u003e\u003cspan address=\"10.1111/j.1365-2664.2009.01664.x\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[{"identity":"7283dfe3-8048-4091-a70d-39ae253a5ef4","identifier":"10.13039/501100006668","name":"Fondo para la Investigación Científica y Tecnológica","awardNumber":"PICT 2019 01161","order_by":0}],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"CICyTTP (CONICET)","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":"multi-species occupancy, woodland specialists, non-woodland species, avian assemblages, canopy cover, tree diameter, xerophytic woodlands","lastPublishedDoi":"10.21203/rs.3.rs-8928094/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8928094/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eDry forests and woodlands are valuable yet fragile ecosystems prone to rapid degradation and structural simplification by overuse, including livestock grazing, fire, and logging. In these systems, forest birds depend on vegetation structural complexity to meet key foraging and breeding needs, making them sensitive indicators of habitat condition. We assessed bird occupancy in the Espinal woodlands of east-central Argentina, testing whether assemblage- and species level occupancy patterns of woodland specialists\u0026rsquo; and non-woodland birds were related to vegetation structure and mediated by habitat affinity. Using a hierarchical occupancy model under Bayesian framework, we found that woodland specialists were associated with sites featuring closed canopies and larger trees, whereas non- woodland (disturbance-tolerant) species were more frequent open and structurally simplified woodlands. Increasing degradation\u0026mdash;characterized by smaller trees, reduced canopy cover, and increased shrub encroachment\u0026mdash; drove shifts from specialist-dominated assemblages toward those dominated by non-woodland (open-areas and shrubland) species. Several common woodland species showed consistent associations with well-preserved dense woodlands or with mature but more open stands, supporting their potential use as indicators of woodland condition. Although maintaining high canopy cover and large trees is essential for conserving disturbance-sensitive woodland bird assemblages, some insectivorous species restricted to xerophytic woodlands preferred mature stands with open understories, underscoring the importance of structural heterogeneity. Our results highlight the value of detectability-corrected occupancy modeling for identifying assemblage- and species-level responses to woodland degradation and for guiding conservation-oriented management in livestock-grazed dry woodlands.\u003c/p\u003e","manuscriptTitle":"Vegetation structure shapes occupancy patterns of specialist and non-specialist birds in xerophytic woodlands","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-02 03:45:09","doi":"10.21203/rs.3.rs-8928094/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":"42e3aaee-7ae6-4f5a-89f4-c4f6518d5a4e","owner":[],"postedDate":"March 2nd, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":63658006,"name":"Terrestrial Ecology"}],"tags":[],"updatedAt":"2026-03-02T03:45:09+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-02 03:45:09","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8928094","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8928094","identity":"rs-8928094","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}