Agonistic behaviour of Mediterranean Peregrine Falcons during the breeding season: defending cliff territories from intruders

Agonistic behaviour of Mediterranean Peregrine Falcons during the breeding season: defending cliff territories from intruders | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL This is a preprint and has not been peer reviewed. Data may be preliminary. 12 January 2026 V1 Latest version Share on Agonistic behaviour of Mediterranean Peregrine Falcons during the breeding season: defending cliff territories from intruders Authors : Maurizio Sarà 0000-0003-4274-422X [email protected] and Laura Zanca Authors Info & Affiliations https://doi.org/10.22541/au.176826080.07970791/v1 319 views 69 downloads Contents Abstract Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract Agonistic interactions play a key role in structuring raptor communities, particularly in cliff-nesting assemblages where space and security are limiting resources. We investigated the frequency, intensity and temporal modulation of agonistic behaviour in a Mediterranean island population of the peregrine falcon Falco peregrinus, focusing on interactions with common ravens Corvus corax and other cliff-dwelling species. Using 15 years of standardised focal observations across 83 nesting cliffs, we quantified aggressive activities and actions and modelled their relationships with cliff characteristics, neighbour proximity, interacting species and breeding stage. Agonistic behaviour occurred at most cliffs, but in a minority of the sampling period (16%), indicating episodic but widespread territorial conflict. The intensity of aggression was primarily shaped by nearest-neighbour distance to other falcons, species-specific interaction asymmetries and breeding stage, rather than by cliff size alone or by social status (neighbour vs intruder). Peregrine falcons showed peak aggression during territorial displays and courtship, followed by a marked decline during incubation and chick rearing, whereas common ravens exhibited a progressive seasonal increase in aggression despite declining investment across breeding stages. These contrasting patterns indicate that seasonal aggression is not universally driven by increasing reproductive value of nest contents but instead reflects species-specific cost–benefit landscapes shaped by territorial rigidity, social structure and life-history strategy. Introduction Territoriality is widely represented among diurnal raptors (Newton 1979). This trait has been significantly modified through recent evolutionary adaptations driven by body size, climate, and habitat changes, thus creating the broad range of territorial patterns that are now strongly associated with the ecology of most species (Martínez-Hesterkamp et al. 2018). Generally, the defence of one’s territory is expressed through both interspecific and intraspecific aggressive exclusion. This array of often spectacular behaviours is predicted to increase when two phylogenetically or ecologically related species occur in sympatry (Wiens 1989, Krüger 2002, Friedemann et al. 2017), and is used to avoid or resolve competition for resources, to establish, defend and maintain territories (Sergio et al. 2004, Martínez et al. 2008, Jiménez-Franco et al. 2011), or to increase reproductive potential (Orians and Willson 1964, Cody 1978). Agonistic behaviour is therefore considered among the key factors structuring raptor communities (Jaksić 1985), with dominance hierarchies often emerging because of body size and competitive ability (Leyequién et al. 2007, Baladrón and Pretelli 2013, Friedemann et al. 2017). In addition to competition, interspecific relationships among raptors are strongly shaped by predation risk, which influences both reproductive ecology and behaviour (Newton 1998, Sergio and Hiraldo 2008). Eggs, nestlings and even adults may be preyed upon by other raptors, owls, corvids, mammals and reptiles (Cramp and Simmons 1980, Ferguson-Lees and Christie 2001), imposing selective pressures on nest placement, concealment and parental investment (Sofaer et al. 2013, Gladow et al. 2025). Patterns and displays of such agonistic behaviours vary depending on the species’ ecology, lifestyle or breeding system (Newton 1979, Cramp and Simmons 1980, Ferguson-Lees and Christie 2001, White et al. 2013) and range from low-intensity displays such as postures, flights and vocalizations (Jamieson and Seymour 1983) to high-intensity actions including chasing, diving and physical attacks (Bildstein and Collopy 1985, Dawson and Mannan 1991). Their frequency and intensity vary with resource limitation, breeding stage and species-specific traits such as sexual size dimorphism (Andersson et al. 1992, Morrison et al. 2006, Boerner and Krüger 2009). Aggressive behaviour can play an important role in individual fitness, as demonstrated by the different colour morphs of the common buzzard ( Buteo buteo ) (Boerner and Krüger 2009). In males, light-coloured individuals show higher levels of aggression towards an interspecific predator compared to intermediate and dark morphs, whereas in females the pattern is reversed. This results in sex-specific differences in aggression between the morphs, potentially leading to differential fitness outcomes (Boerner and Krüger 2009). Territorial responses are also modulated by social context. Many species show reduced aggression towards neighbours compared to unfamiliar intruders (reviewed in Ydenberg et al. 1988, Temeles 1994), a pattern known as ‘the dear enemy effect’ (Fisher 1954). This phenomenon has led to the formulation of the ‘familiarity’ and ‘threat-level’ hypotheses to explain variation in agonistic interactions among territorial competitors. Familiarity between neighbouring individuals is thought to decrease the likelihood of role errors during territorial encounters (Ydenberg et al. 1988), thereby reducing the costs of repeated aggression, including time and energy expenditure and the risk of injury, through the regulation of neighbour relationships (Wilson 1975). Territorial interactions may also provide opportunities for information gathering, allowing individuals to adjust subsequent behavioural strategies (Getty 1989). However, reduced aggression towards neighbours is not universal: in a minority of species (approximately 9% of those examined, Temeles 1990, 1994), responses towards neighbours exceed those directed at strangers. In such cases, an inverse ‘nasty neighbour effect’ (Müller and Manser 2007, Christensen and Radford 2018) may arise, particularly when familiar neighbours represent an unreliable or elevated threat (Godard 1993, Olendorf et al. 2004). During reproduction, aggression is often interpreted through the reproductive value of the nest contents hypothesis, which predicts increasing defence as offspring age and reproductive investment accumulates (Montgomerie and Weatherhead 1988, Redondo and Carranza 1989). While this pattern has been confirmed in common buzzard, where the level of defence against interspecific dummies (goshawks, Accipiter gentilis ) varies according to the age of the offspring but not their number (Krüger 2002), other raptors deviate markedly depending on breeding system, territorial stability and ecological context (Jamieson and Seymour 1983, García and Arroyo 2002). Despite their potential importance in structuring cliff-nesting bird communities, agonistic interactions among cliff-nesting raptors have been quantitatively investigated in relatively few studies (Jenkins and van Zyl 2005, Martínez et al. 2008, Rodríguez et al. 2017). Although comparative analyses have been conducted across several continents, including Australia (Bauer and McDonald 2018), North America (Morrison et al. 2006), and South America (Baladrón and Pretelli 2013), such research remains scarce relative to the global distribution and ecological diversity of raptors. Ground-nesting Holarctic harriers ( Circus spp.) have emerged as particularly suitable model species for the study of territorial and interspecific aggression and have therefore received comparatively greater attention (e.g. Bildstein and Collopy 1985, Temeles 1990, Arroyo et al. 2002, García and Arroyo 2002, Wiącek 2006). For cliff-dwelling species, contributions focus on aggressive interactions involving the peregrine falcon ( Falco peregrinus ) and the common raven ( Corvus corax ) (Brambilla et al. 2004, Sergio et al. 2004). Similar interactions have been documented between prairie falcons ( Falco mexicanus ) and peregrine falcons or common ravens (Holthuijzen and Oosterhuis 2004, Dekker and Corrigan 2006), as well as between their vicariant taxa in Australia, namely Falco subniger and Corvus coronoides (Bauer and McDonald 2018). We investigated patterns of agonistic interactions associated with cliff-nest defence in a Mediterranean island population of the peregrine falcon, in relation to the common raven and other members of the cliff-nesting bird community. Cliffs host high levels of biodiversity and support specialised avian assemblages, including species nesting on ledges, in crevices or caves, or laying eggs in shallow scrapes, often under conditions of intense interspecific competition for limited nesting sites (Krajick 1999, Newton 1998, Covy et al. 2020). As a nearly cosmopolitan, medium-sized apex predator, the peregrine falcon typically dominates cliff bird communities (Jenkins and van Zyl 2005, White et al. 2013). Although coexistence with common ravens may reduce peregrine falcon breeding success (Brambilla et al. 2004), several studies have reported positive effects of spatial proximity between the two species (Sergio et al. 2004, Jenkins and van Zyl 2005, Rodríguez et al. 2017). Accordingly, under the familiarity hypothesis, we predict reduced reciprocal aggression and generally low-intensity agonistic interactions between coexisting peregrine falcon and common raven pairs compared with responses to unfamiliar intruders. Moreover, agonistic behaviour is expected to vary temporally across the breeding season, in line with predictions of the reproductive value of nest contents hypothesis. We quantified the frequency and intensity of peregrine falcon agonistic behaviour towards neighbouring common ravens and other cliff-nesting species. In more detail, we tested whether agonistic behaviour varied with (i) physical characteristics of cliffs and nearest-neighbour distances, (ii) identity and social status of interacting species, and (iii) breeding stage and seasonal timing. Materials and Methods Sampling protocol The Sicilian population of the peregrine falcon is currently assigned to the Mediterranean subspecies F. p. brookei (White et al. 2013, Mengoni et al. 2018). Peregrine falcons are quite common in Sicily, with a current population of about 275 pairs on the main island and the small neighbouring islands (Sarà et al. 2023). The population is spread in all the natural and semi-natural habitats, nesting in both small crags and large cliffs from sea level to 1424 m a.s.l., but it is rarer in the densely forested habitats of the north-eastern ridge. The common raven is also resident and widespread throughout the island from sea level up to 1600 m a.s.l. occupying the same habitats as the peregrines (AA.VV. 2008, Salvo 2015, Mascara 2017). Even in Sicily, peregrine falcon and common raven often coexist in the same nesting cliff and engage in territorial disputes during the breeding season (Salvo 2015, Mascara 2017, AA. unpublished data). A substantial part of the peregrine falcon populations of Sicily is monitored (e.g. Sarà et al. 2023) and this implies that the common raven population, that coexists in 70% of the cliff sample, has also been studied with the same protocol. Visits to the cliffs begin between late January and early February and end in mid-June to cover the biological activities of the peregrine falcon pairs, from mating to fledging chicks, using non-rainy days and with clear skies and varying the monitoring time of each area from one visit to another. Peregrine falcons occupy the eyrie and lay eggs before common ravens, but they have a shorter incubation period and faster chick growth than peregrine falcons, so coexisting common ravens fledge at about the same time of the peregrine falcons (Salvo 2015, Zuberogoitia 2023, AA. unpublished data). The cliffs and their occupants were observed from vantage points located quite far away (mean ± SD = 503.5 ± 260.8, range: 100-1310 m, n = 96) to minimize disturbance to nesting species. The cliffs were scanned using 10x42 binoculars and a 20-60x telescope, so that one ‘telescope-observer’ always focused on the pair mates perched in the cliff and/or their nests, while the other ‘binocular-observer’ always focused on the mates’ flights back and forth to the cliff and the activities of the other birds around. This protocol made it possible to efficiently maximize observation sessions, facilitating the recording of activity and behaviour of falcons, common ravens, other cliff nesters and species in transit along the cliffs. We recorded the aggressive responses to intruders who passed through the nesting areas and all the agonistic behaviours of peregrine falcons, common ravens and other species (such as lanner falcon Falco biarmicus , common kestrel Falco tinnunculus , lesser kestrel Falco naumanni , common buzzard, etc.) nesting in cliffs. Birds involved in agonistic behaviours were determined at species level. Visits at cliffs were planned according to the following protocol: the initial (arrival) and final (departure) time (2-10 min on average) made it possible to prepare the equipment for focal observations and were not calculated. Then focal observations started and were divided up into successive sample intervals of 20 min in which the breeders’ presence (all species nesting in the cliff up to the size of the black starling) and biological activities of focal species (peregrine falcon and common raven) were recorded. The sample interval of 20 min was followed by one pause of 10 min, in which meteorological conditions and other relevant data, like the number of pigeons and doves, presence of transient species, etc. were recorded. Then another 20+10 min of sampling (hereafter time slot) was repeated until the end of daily visit. With the above schedule and from 2010 to 2025 we recorded the agonistic interactions of cliff dwellers during 1268 visits in 83 sites (mean ± SD = 15.3 ± 14.4, range: 1-66 visits per site); totalling 2506 time slots equivalent to 1373 hours and 49 minutes of net observations of the cliffs in which peregrine falcons, common ravens and their avian neighbours attempted to breed. Territorial and warning display of raptors and common raven are sufficiently known (Cramp and Simmons 1980, Ratcliffe 1997, Ferguson-Lees and Christie 2001). We defined an agonistic interaction as the aggressive activity against an opponent during which the focal bird engaged in aerial displays with or without vocalization. The only vocal call of a bird perched or in flight, was not considered, because it can be interpreted in many ways and was often out of sight of the observers. Aggressive activities are a complex or lengthy sequence of behaviour involving two to many action patterns (Ellis and Schmidt 2017) that we categorized as: a) attack, i.e. plunges/chases/dives with or without vocalization; b) warning, i.e. single or multiple directional or circular patrol back and forth along the cliff; escort flights with or without vocalizations; or c) mixed, i.e. attack and warning. One or more of these activities may occur in separate moments of each 20-minute time slot. The number of time slots and the respective number of activities that occurred relative to the total sample of time slots provided an estimate of the frequency of agonistic behaviour. On the other hand, activities can include single or multiple chases, dives, escort flights, etc (action patterns, see Ellis and Schmidt 2017). Counting these action patterns (hereafter, actions for brevity) occurring in the 20 minutes of each time slot instead provided a measure of the intensity of the agonistic behaviour. For example, let’s consider a time slot in which three activities and six actions against a common raven were recorded: the peregrine falcon first engaged in a single escort flight at minute x of the slot (first [warning] activity with one action); then, at minute x +2, he did three circular patrol flights along the cliff (second [warning] activity with three actions); and finally plunged two times with alarm calls at minute x +6 (third [attack] activity with two actions). Actions can be either discrete (e.g. one or two dives or patrol flights of few seconds, clearly separated from each other in time) or form more complex and long bouts (i.e. performances of one or more actions pattens for a given time, e.g. an attack bout of 3, 5, etc minutes, see Ellis and Schmidt 2017). Actions were counted when clearly discrete. In case of longer and continuous bouts, the time sequences were equated to discrete actions in this way: 1 bout up to 3 min = 5 actions, 1 bout 3 to 5 min = 10 actions, etc, to standardize the actions counting. In each time slot, the species that first attacked and the recipient species were recorded. However, since the direction of the interaction is very often reversed because the species that first attack/warn the peregrine falcon or the common raven in turn become attacked and chased, here we simply considered the interacting species and not the direction of their interaction (who attacks whom). All chases upon well-known prey (e.g. swifts, pigeons, doves, starlings, jackdaws, etc.) that occurred along the cliffs, or warning and other defensive reactions of these potential preys to peregrine falcon were also recorded but later removed as considered not pertinent to this study. Only a minority of activities between kestrels – four with the common kestrel, two with the lesser kestrel – and the peregrine falcon were included because undoubtedly judged to be the result of an agonistic interaction and not a predation attempt against these occasionally preyed kestrels (Cramp and Simmons 1980, Bondì et al. 2016, Zuberogoitia 2023). Data Modelling To model the agonistic interactions of the peregrine falcons and the nesting community in the cliffs, we used a negative binomial generalized linear model with a log link function, appropriate for overdispersed count data, i.e. with the variance greater than mean (Agresti 1996). Indeed, the response variable of the negative binomial models was the number of actions for each of the 299 activities and the categorical variable ‘striker’ with three levels: ‘peregrine’, ‘raven’, and ‘other’ identified cliff dwellers who performed agonistic actions. Both variables were used in negative binomial models that considered the effects of: a) Cliff features (height_cliff and length_cliff) and distance from the nearest-neighbour falcon (comprising both peregrine and lanner falcons) and common raven (NND falcon, NND raven). The explanatory variables of this model are continuous variables (in metres) that were standardized prior to analysis (Schielzeth 2010). The checks of collinearity did not detect any linear relationship (VIF ≥ 3) in the explanatory variables. A two-factor factorial design was employed to detect all possible combinations of cliff features and NND distances on the number of actions performed by the three strikers. We hypothesized that the smaller cliffs and/or the shorter nearest-neighbour distances would elicit more territorial disputes with many more agonistic activities than the opposite. b) Recipient species (peregrine, raven, other) and its status (neighbour, intruder). The explanatory variables of this model included here categorical variables that grouped the recipient identity (i.e. the species that received the agonistic interaction) into: ‘peregrine’, ‘raven’, ‘other’, and were also classified as ‘neighbour’ or ‘intruder’, according to the breeding status and phenology of birds in Sicily (Lo Valvo et al. 1993, AA.VV. 2008, Lardelli et al. 2022). Neighbours are resident and summer species nesting in the same cliffs or in the immediate vicinity (≤ 500 m) of the focal pair. Intruders can be resident; summer breeding and wintering species present in more distant areas or simply migrants passing through during their pre-nuptial journeys. The checklist of recorded striker and recipient species, categorized by their neighbour or intruder status and with the mean number of activities and actions per species is reported in Table S1, ESM. A two-factor factorial design was employed to detect the main effects of striker, recipient and status and the related interactions (striker x recipient and striker x status). The interaction between recipient identity and status was not included because preliminary model comparisons indicated no improvement in model fit, and because status reflects the social context of the interaction rather than an intrinsic property of the recipient. With this model, according to the familiarity hypothesis (Ydenberg et al. 1988), we assumed a differential recognition of the opponent, and we hypothesized that neighbour recipients elicit less aggression and agonistic interactions than intruder ones. c) Seasonal trend and timing of the breeding season. In this circumstance, we restricted the analysis to the peregrine falcon and the common raven, the focal species of cliff visits. The samples of agonistic activity involving peregrine falcons (n = 196) and common ravens (n = 164) were modelled independently to account for differences in the timing of their breeding seasons (Cramp and Simmons 1980, Cramp and Perrins 1994, Salvo 2015, Zuberogoitia 2023). The reproductive season of each species was divided in three stages (1. territorial displays and courtship, 2. laying and incubation, 3. brooding and fledging). Seasonal trends were modelled using Julian day as a centered linear and quadratic term of the negative binomial GLM, allowing non-linear seasonal patterns to emerge from the data while retaining all observations. Although breeding stage and Julian day both reflect temporal progression, they capture different dimensions of time: breeding stage represents internal reproductive constraints, whereas Julian day reflects external seasonal conditions. Their joint inclusion allows disentangling functional changes in nesting behaviour from broader seasonal trends. We hypothesized that territorial behaviour of peregrine falcon and common raven during the breeding season is stage dependent. Therefore, we expect an increasing intensity of territorial defence and aggressive interactions during nesting progression, i.e. as the nest contents grow in age and its relative reproductive value increases, with the late brooding phase eliciting a greater response from parents of both species (Montgomerie and Weatherhead 1988, Redondo and Carranza 1989). All models were performed independently with mean centered predictor variables. Complex models with many parameters (k) to be estimated compared to the number of observations (n) were avoided and interaction terms were included only when biologically and statistically justified and produced models respected the most conservative ratio cited in the literature (n/k ≥ 10; Harrison et al. 2018). Statistical significance was set in all analyses at p < 0.05. Statistics were computed in the module GAMLj v. 3.5 (General Analyses for Linear Models) of the JAMOVI project (https://www.jamovi.org.) and PAST 4.10 (Hammer et al. 2001). Results Attack and warning behaviours occurred in 211 visits, 16.6% of the total (n = 1268), and in 258 time slots, 10.3% of the total (n = 2506). Overall, 299 agonistic activities (mean ± SD = 1.42 ± 0.84) comprising 1057 actions (mean ± SD = 3.54 ± 3.68) were recorded (Table S1, ESM). The most frequent aggressive interactions of peregrine falcons were against neighbouring common ravens (19.4% of activities and 19% of actions) and against Eurasian buzzard intruders (12% of activities and 11.7% of actions). While the common raven directed its agonistic interactions against Eurasian buzzard both intruders (6.4% of activities and 7.4% of actions) and neighbouring (2.7% of activities and 2.6% of actions), then against neighbouring peregrine falcons (3.7% of activities and 1.7% of actions). Four other raptors and two corvids, with the common kestrel being the most aggressive of the six, form the group of ‘other’ strikers (Table S1, ESM). Agonistic interactions were observed in 66.3% of the 83 monitored cliffs, indicating that although episodic, aggression was widespread across the study area. The probability of recording agonistic interactions increased with observation duration. The number of activities per visit was significantly influenced by the number of time slots sampled (F ( ₆ , ₂₀₄ ) = 6.36, p < 0.001; Fig. S1, ESM). Visits lasting five time slots (approximately 2.5 hours of observation) yielded an average of 2.44 ± 1.88 aggressive activities, suggesting that shorter visits likely underestimate interaction frequency. Do the characteristics of the cliff elicit agonistic interactions? The full negative binomial model including cliff characteristics and nearest‐neighbour distances showed a significant improvement over the null model (χ² (20) = 38.2, p = 0.008), indicating that spatial and structural variables jointly explained a significant portion of variation in the number of aggressive actions. Model explained 12.8% of variance (R² = 0.128; adjusted R² = 0.065), and residual overdispersion was adequately accounted for (χ²/df = 1.32). Among main effects, nearest‐neighbour distance to falcons (NND falcon) was the only predictor showing a significant overall effect (χ² (1) = 7.95, p = 0.005). Specifically, increasing NND falcon was associated with a reduction in the expected number of aggressive actions (β = −0.215 ± 0.077 SE), corresponding to an approximate 19% decrease per standard deviation increase (Exp(β) = 0.81; Fig. 1a). All other main predictors—cliff length, cliff height, NND raven, and striker identity—are not significant (p > 0.10), indicating that their global effects do not manifest as consistent context-independent averages. Rather, several interaction terms exhibited significant effects, indicating that the influence of some predictors varied depending on the levels of others. In particular, the interaction between NND falcon and striker identity was significant (χ² (2) = 8.36, p = 0.015). This effect was driven primarily by the contrast between other species and peregrines (β = −0.398 ± 0.137 SE, p = 0.004), indicating that the negative relationship between NND falcon and action frequency was strongest when aggressive actions were performed by species other than peregrines (Fig. 1b). A significant interaction was also detected between NND falcon and cliff length (χ² (1) = 6.78, p = 0.009). Simultaneous increases in NND falcon and cliff length resulted in an additional reduction in aggressive actions (β = −0.249 ± 0.096 SE, p = 0.010), indicating a non‐additive combined effect of spatial scale and habitat extent (Fig. 2). In addition, the interaction between NND raven and NND falcon was significant (χ² (1) = 5.26, p = 0.022). The negative coefficient (β = −0.188 ± 0.084 SE, p = 0.025) indicates that the effect of increasing distance to one competitor weakened as distance to the other increased, suggesting overlapping spatial constraints within cliff communities (Fig. S2, ESM). Two additional interactions—cliff length × striker identity (p = 0.060) and cliff height × NND raven (p = 0.054)—were marginally significant, suggesting further context‐dependent effects that may emerge more clearly with larger samples or seasonally explicit models. Who elicits the aggressive response? The negative binomial model including striker identity, recipient identity, recipient status (intruder vs neighbour), and their interactions was significant overall (χ² (11) = 20.5, p = 0.039) and explained 7% of variance (R² = 0.070; adjusted R² = 0.034). Residual overdispersion was adequately accounted for (χ²/df = 1.36). The main effect of striker identity was not significant (χ² (2) = 2.11, p = 0.349), indicating that no species initiated more aggressive actions than others on average. Similarly, recipient status had no effect (χ² (1) = 0.141, p = 0.707), with intruders and neighbours receiving comparable levels of aggression. Recipient identity showed a marginal effect (χ² (2) = 4.95, p = 0.084), with peregrine falcons tending to receive fewer aggressive actions than other species (β = 0.334 ± 0.181 SE, Exp(β) = 0.716, p = 0.065). In contrast, the interaction between striker and recipient identity was significant (χ² (4) = 12.47, p = 0.014), indicating that aggression intensity depended on the specific combination of interacting species. Common ravens directed significantly fewer aggressive actions towards peregrine falcon recipients compared to the other species (β = 0.894 ± 0.431 SE, Exp(β) = 0.41, p = 0.038; Fig. 3). The interaction between striker identity and recipient status approached significance (χ² (2) = 5.01, p = 0.082), suggesting a tendency for common ravens and other species to direct more aggression towards neighbours than intruders, whereas peregrine falcons showed the opposite tendency, although neither pattern reached conventional significance (Fig. 4). When do agonistic interactions take place? The model testing variation in peregrine falcon aggressive actions across breeding stages showed a significant overall fit (χ²(4) = 16.6, p = 0.002), explaining 8.7% of variance (R² = 0.087; adjusted R² = 0.067) and being appropriate for overdispersed count data (χ²/df = 1.44). Breeding stage significantly affected aggression intensity (χ² (2) = 10.33, p = 0.006). Compared to the territorial displays and courtship phase, aggression was significantly lower (≈ 43%) during laying and incubation (β = −0.56 ± 0.19 SE, Exp(β) = 0.571, p = 0.003) and during brooding and fledging (β = −0.56 ± 0.22 SE, Exp(β) = 0.574, p = 0.010), with no difference between the latter two stages (Fig. 5a). Post hoc comparisons confirmed that aggressive interactions were approximately 1.7 times more frequent during territorial displays and courtship than during either during laying and incubation (z = 2.920, p = 0.01) or brooding and fledging (z = 2.568, p = 0.03). Seasonal effects revealed a non‐linear temporal pattern between aggression and time. While the linear effect of Julian day was not significant (β = −0.004 ± 0.003 SE, p = 0.246), the quadratic term was negative and significant (β = −1.43 × 10⁻⁴ ± 7.15 × 10⁻⁵ SE, p = 0.046), indicating a concave‐down seasonal pattern. Predicted aggression peaked around Julian day 91 (late March–early April), corresponding for many pairs to the end of incubation or the first hatchings (Fig. 6a). The common raven model also showed a significant overall fit (χ² (4) = 9.71, p = 0.046), although explanatory power was 6% (R² = 0.06; adjusted R² = 0.036). Breeding stage significantly influenced aggression intensity (χ² (2) = 7.88, p = 0.019). Relative to territory acquisition, aggression decreased during incubation (−41%), albeit marginally (β = -0.528 ± 0.283 SE, Exp(β) = 0.590, p = 0.062) and declined more strongly (−65%) during brooding and fledging (β = -1.058 ± 0.385 SE, Exp(β) = 0.347, p = 0.006). Estimated marginal means indicated a progressive decline in aggression across breeding stages, from approximately 6.7 actions during territory acquisition to 4.0 actions during incubation and 2.3 ones during brood and fledging. These results suggests that aggression in common ravens is shaped by two concurrent gradients. First, a gradual reduction in aggressive behaviour as the breeding season progresses, which is highest during territorial displays and courtship and lowest during brooding and fledging (Fig 5b). Second, independent of breeding stage, aggressive interactions increase linearly over the course of the breeding season, with no indication of a mid-season peak or decline (Fig. 6b). Marginal predictions indicated that aggressive interactions increased from approximately 2.7 to 5.8 actions across the observed range of Julian day, after controlling for breeding stage. Discussion Agonistic interactions play a central role in structuring avian communities, particularly in territorial and resource-limited environments such as cliff ecosystems (Newton 1998). In raptors, aggressive behaviours contribute to the defence of nesting sites (Cramp and Simmons 1980), regulation of spatial overlap (Kostrzewa 1996), and mediation of interspecific competition, thereby influencing both individual fitness and community dynamics (Sergio et al. 2007, Chen et al. 2022). Despite their ecological relevance, quantitative assessments of agonistic interactions in cliff-dwelling raptor assemblages remain scarce, especially from a comparative, long-term perspective. Our study addresses this gap by examining the occurrence, determinants, and seasonal dynamics of agonistic interactions involving peregrine falcons and common ravens within a multi-species cliff community. Although agonistic interactions accounted for approximately 16% of recorded visits, their occurrence across most monitored cliffs and their positive association with visit duration indicate that such behaviours represent a recurrent and non‐trivial component of cliff use during the breeding season. Given that detectability increases with observation time, extending monitoring to cover the full reproductive period would likely reveal an even higher prevalence of agonistic interactions within this community. Continuous or automated recording could further refine estimates of interaction frequency and intensity, allowing assessment of interannual and site‐specific variation driven by fluctuating resource availability, habitat quality, or environmental conditions. For example, adverse weather has been shown to intensify aggressive behaviour in birds of prey by increasing energetic constraints and competitive pressure (Temeles and Wellicome 1992). Do cliff characteristics elicit agonistic interactions? Spatial configuration plays a key role in shaping agonistic behaviour, but its effects vary according to the surrounding ecological conditions. Nearest neighbour distance between peregrine falcons emerged as the primary structural predictor of action intensity; however, its effect varied according to striker identity, cliff length, and proximity to common raven territories. The presence of significant interactions indicates that agonistic behaviour emerges from the interplay between spatial structure and social context, rather than from single habitat variables. Peregrine falcons are known to select high cliffs disproportionately relative to availability (Arambarri and Rodríguez 2000, Jenkins and van Zyl 2005, Wilson et al. 2018), likely because such sites provide extensive visibility, early detection of intruders, and potential advantages in prey interception (Mooney and Brothers 1987, Ratcliffe 1993). However, cliff size is a composite feature, encompassing not only vertical height but also horizontal extent (length) and overall structural prominence, all of which may contribute to breeding performance and are consistent with reported associations between cliff size and productivity (Sergio et al. 2004). Although cliff height could be expected to increase competition, our analyses found no significant effect on agonistic interaction frequency. This pattern suggests that height by itself may not adequately capture the functional value of nesting cliffs of our sample areas, and that other size-related attributes, such as length, may play an important role. Instead, more complex models incorporating breeding stage, temporal variation, and multiple cliff attributes simultaneously may be required to capture how physical structure modulates aggression. Who elicits the aggressive response? Aggressive responses were not uniformly distributed across species or social status (intruder versus neighbour) but instead depended on specific dyadic combinations. Neither striker identity nor social status alone explained variation in aggression intensity, contradicting simple dominance‐based or status‐driven models. Rather, aggression emerged as an outcome shaped by the identities of both interacting individuals, as indicated by the significant striker × recipient interaction. Aggression would therefore be modulated by asymmetric costs and benefits associated with confronting different opponents (Maynard Smith and Parker 1976, Hsu et al. 2006). The reduced aggression shown by common ravens towards peregrine falcons likely reflects risk-sensitive decision-making, with escalation avoided when potential costs outweigh expected benefits (Enquist and Leimar 1983, Arnott and Elwood 2009). This opponent-specific modulation of aggression aligns with game theory and contest models, where behaviour is adjusted to expected payoffs rather than absolute dominance (Maynard Smith 1982, Briffa and Sneddon 2007). The absence of a clear main effect of social status also challenges the traditional “dear enemy” versus “nasty neighbour” framework (Fisher 1954, Temeles 1994). Although peregrine falcons tended to direct defensive behaviour more often towards intruding species, aggression intensity was not consistently higher towards intruders than neighbours. This indicates that territorial familiarity alone does not structure aggressive responses in this system (Stamps and Krishnan 2001). Instead, territorial dynamics likely interact with species identity, prior experience, and perceived threat, producing flexible and conditional behavioural strategies rather than fixed territorial rules (Getty 1987, Peiman and Robinson 2010). At the behavioural level, these patterns support the interpretation of aggression as a plastic and strategic trait (West-Eberhard 2003). The tendency for common ravens to show increased aggression towards neighbours, although not statistically conclusive, may reflect repeated interactions, accumulated conflicts, or long-term competition for shared resources (Temeles 1990, Müller and Manser 2007). Such responses are consistent with behavioural adjustment mediated by learning and memory, whereby individuals modulate aggression based on past encounters rather than immediate context alone (Dukas 1999, Stamps and Groothuis 2010). When do agonistic interactions take place? Aggressive behaviour during the breeding season is often interpreted through the reproductive value of the nest contents hypothesis (Montgomerie and Weatherhead 1988, Redondo and Carranza 1989). However, this framework implicitly assumes that the benefits of escalating aggression consistently outweigh its costs throughout the breeding cycle. Our comparative results demonstrate that this assumption does not hold universally. In peregrine falcons, aggression peaked during territorial displays and courtship and declined thereafter, despite the increasing reproductive value of eggs and offspring. Breeding stage exerted a strong and consistent effect, and seasonal covariates revealed a clear concave temporal pattern, indicating that aggressive behaviour in peregrine falcons is strongly structured by both breeding stage and seasonality. This strongly suggests that aggression is a context-dependent trait, shaped by reproductive and territorial needs. Peregrine falcon pairs, from non-migratory populations such as F. p. brookei , occupy their territories year-round. As nesting season approaches, territorial activities become increasingly focused on the cliff, where courtship and copulation take place. The highest intensity of aggression during the territorial displays and courtship phase suggests that these interactions play a key role in establishing and defending breeding territories. At this stage, competition for suitable nesting sites and spatial dominance is likely to be most intense, favouring escalated aggressive behaviour. The marked reduction in aggression during incubation and brooding/fledging indicates a shift in behavioural priorities, where energy and time are increasingly allocated to parental care rather than territorial disputes (e.g. Wingfield et al. 1990, Katsis et al. 2025). The seasonal pattern further refines this interpretation. The concave-down relationship between aggression and Julian day reveals a pronounced peak in late March–early April. This timing coincides with the delicate moment of end of incubation and early births, suggesting that aggression reaches its adaptive maximum before reproductive investment becomes constrained by chick rearing. Rather than supporting the reproductive value hypothesis, peregrine falcon behaviour indicates a strategic concentration of aggression at the phase where territorial exclusion yields the highest fitness returns. Importantly, the decline in aggression after this peak may reflect both reduced benefits and increased costs of aggressive behaviour as breeding progresses. Once territories are established and reproductive activities intensify, further aggression may offer diminishing returns and could even compromise reproductive success through increased energetic expenditure or injury risk (e.g. George et al. 2024). This stage-dependent and seasonally constrained pattern highlights the importance of considering both temporal and reproductive contexts when interpreting aggressive behaviour in territorial raptors. This strategy is consistent with the peregrine falcon’s life history as a long-lived, high-investment predator with strong site fidelity and low tolerance for adult mortality. In such species, selection is expected to favour conservative risk management, with adult survival taking precedence over marginal gains in nest defence as offspring value increases (Ghalambor and Martin 2001, Zabala and Zuberogoitia 2015). Common ravens showed a contrasting pattern. Like peregrine falcons, breeding pairs exhibit strong fidelity to their nesting territories; consequently, defended areas, although variable in size and not always exclusive to pairs, tend to concentrate near the nesting cliff as the breeding season progresses. Although aggression was also highest during territorial displays and courtship and declined across breeding stages, it increased linearly with seasonal progression, indicating that antagonistic behaviour intensified as the breeding season advanced. This suggests that, in common ravens, aggressive investment continues to track increasing reproductive value, rather than being confined to early territorial establishment. The common raven’s flexible territorial system and complex social ecology likely facilitate this response. Common ravens engage in frequent interactions with conspecifics and heterospecifics, and balance aggression with other social strategies (Heinrich 1989, Bugnyar and Kotrschal 2002, Freeman and Miller 2018). In this context, aggression may serve multiple adaptive functions beyond strict nest defence, including deterrence, dominance maintenance, and resource competition. As a result, the costs of aggression are less tightly constrained, allowing behaviour to increase over time even as reproductive demands intensify. Taken together, these results indicate that seasonal patterns of aggression cannot be explained by reproductive investment alone but are contingent on species-specific cost–benefit landscapes (e.g. Dale et al. 1996; Crisologo and Bonter 2017). Conclusion Our long-term analysis indicates that agonistic interactions in cliff-dwelling birds cannot be explained by increasing reproductive value alone, nor by classic frameworks such as the dear enemy effect. Across the studied cliff-dweller community, aggression was widespread but episodic, structured primarily by breeding stage, opponent identity, and local spatial context. The contrasting seasonal trajectories observed between peregrine falcons and common ravens illustrate how differences in territorial rigidity, tolerance of risk, and social interaction regimes generate distinct cost–benefit landscapes for aggression, even within the same physical environment. Despite frequent agonistic interactions, coexistence between peregrine falcons and common ravens occurs in 70% of monitored cliffs. This pattern is consistent with the behavioural mediation of competition in cliff-nesting raptors (Peiman and Robinson 2010), whereby interference interactions influence spatial overlap and access to nest sites without necessarily leading to competitive exclusion (Carrete et al. 2006, Sergio et al. 2007). Peregrine falcons may tolerate or even select breeding sites close to those of aggressive heterospecific species, such as common ravens, likely due to their early warning activities, which offers anti-predator and energy-saving benefits (cf. Campobello et al. 2012), or other ecological advantages (Sergio et al. 2004). In contrast, corvids often adapt behaviour through temporal or spatial avoidance rather than direct displacement (Bugnyar and Kotrschal 2002). Within this framework, agonistic behaviour emerges as a flexible regulatory mechanism that structures interspecific relationships rather than enforcing strict spatial segregation. Species-specific modulation of aggression across breeding stages and seasons may therefore facilitate stable co-occupation of nesting habitats by ecologically similar cliff-nesting birds. More broadly, our findings highlight the need to adopt a community-level perspective that integrates spatial structure, temporal dynamics, and species-specific behavioural strategies when assessing how agonistic interactions shape the organisation and persistence of cliff-nesting bird assemblages. Data Availability Statement The data that support the findings of this study are available from the corresponding author upon reasonable request. The data are not publicly available due to their association with sensitive breeding sites of protected raptor species. REFERENCES AA.VV., 2008. Atlante della Biodiversità della Sicilia: Vertebrati terrestri. – Studi, Ricerche Arpa Sicilia, Palermo, 6: 1–535. Agresti, A. 1996. An introduction to categorical data analysis. – Wiley. Andersson, M., Wiklund, C. G. and Rundgren, H. 1992. Seasonal and sexual variation in territorial aggression in the European kestrel Falco tinnunculus . – Anim. Behav. 44: 327–336. Arambarri, R. and Rodríguez, A. F. 2000. Breeding density, habitat selection and reproductive rates of the Peregrine Falcon Falco peregrinus in Álava (northern Spain). – Bird Study 47: 225–231. Arnott, G. and Elwood, R. W. 2009. Assessment of fighting ability in animal contests. – Anim. Behav. 77: 991–1004. Arroyo, B. E., de Cornulier, T. and Bretagnolle, V. 2002. Parental investment and parent–offspring conflict during the post-fledging period in Montagu’s harrier. – Anim. Behav. 63: 235–244. Baladrón, A. V. and Pretelli, M. G. 2013. Agonistic interactions in raptors of the Pampas region. – Wilson J. Ornithol. 125: 650–655. Bauer, S. and McDonald, P. G. 2018. Aggressive interactions between sympatric falcons and corvids. – Emu 118: 15–24. Bildstein, K. L. and Collopy, M. W. 1985. Escorting flight and agonistic interactions in wintering Northern Harriers. – Condor 87: 398–401. Boerner, M. and Krüger, O. 2009. Aggression and fitness differences between plumage morphs in the common buzzard Buteo buteo . – Behav. Ecol. 20: 180–185. Bondì, S., Guzzo, E., Vitale, E., Baragona, A., Grancagnolo, D. and Sarà, M. 2016. Factors affecting the diet of Peregrine Falcon in Italy. – Avocetta 40: 1–10. Brambilla, M., Rubolini, D. and Guidali, F. 2004. Rock climbing and Raven occurrence depress breeding success of cliff-nesting Peregrines. – Ardeola 51: 425–430. Briffa, M. and Sneddon, L. U. 2007. Physiological constraints on contest behaviour. – Funct. Ecol. 21: 627–637. Bugnyar, T. and Kotrschal, K. 2002. Observational learning and the raiding of food caches in ravens, Corvus corax : is it ‘tactical’ deception? – Anim. Behav. 64: 185–195. Campobello, D., Sarà, M. and Hare, J. F. 2012. Under my wing: lesser kestrels and jackdaws derive reciprocal benefits in mixed-species colonies. – Behav. Ecol. 23: 425–433. Carrete, M., Sánchez-Zapata, J. A., Tella, J. L., Gil-Sánchez, J. M. and Moleón, M. 2006. Components of breeding performance in two competing species: habitat heterogeneity, interference competition and density dependence. – Oecologia 147: 163–172. Chen, K. H., Lin, W. L. and Lin, S. M. 2022. Competition between the black-winged kite and Eurasian kestrel led to population turnover at a subtropical sympatric site. – J. Avian Biol. : e03040. Christensen, C. and Radford, A. N. 2018. Dear enemies or nasty neighbours? – Behav. Ecol. 29: 1004–1013. Cody, M. L. 1978. Habitat selection and territoriality among sylviid warblers. – Ecol. Monogr. 48: 351–396. Covy, N., Keeley, W. H. and Benedict, L. 2020. Cliff-dwelling birds show variable behavioural responses to rock climbing. – Nat. Areas J. 40: 245–251. Cramp, S. and Perrins, C. M. 1994. Handbook of the birds of Europe, the Middle East and North Africa. Vol. 8. – Oxford Univ. Press. Cramp, S. and Simmons, K. E. L. 1980. Handbook of the birds of Europe, the Middle East and North Africa. Vol. 2. – Oxford Univ. Press. Crisologo, T.L. and Bonter, D.N. 2017. Defending the Weak: Parental Defense Peaks When Chick Vulnerability is Greatest in the Herring Gull ( Larus argentatus ). – Ethology, 123: 113-122. Dale, S., Gustad, J. R., Slagsvold, T. and Lorentsen, S. O. 1996. Risk taking during parental care: a test of the harm-to-offspring hypothesis. – Behav. Ecol. 7: 83–88. Dawson, J. W. and Mannan, R. W. 1991. The role of territoriality in the social organization of Harris’ Hawks. – Auk 108:661–672 Dekker, D. and Corrigan, R. 2006. Population fluctuations and agonistic interaction of peregrine and prairie falcons. – J. Raptor Res. 40: 255–263. Dukas, R. 1999. Costs of memory: ideas and predictions. – J. Theor. Biol. 197: 41–50. Ellis, D. H. and Schmidt, N. J. 2017. Behavior of the Golden Eagle: an illustrated ethogram. – Hancock House. Enquist, M. and Leimar, O. 1983. Evolution of fighting behaviour: decision rules and assessment of relative strength. – J. Theor. Biol. 102: 387–410. Ferguson-Lees, J. and Christie, D. A. 2001. Raptors of the world. – Christopher Helm. Fisher, J. 1954. Evolution and bird sociality. In: Huxley, J., Hardy, A. C. and Ford, E. B., (eds), Evolution as a process. – Allen & Unwin, pp. 71–83. Freeman, B. G. and Miller, E. T. 2018. Why do crows attack ravens? The roles of predation threat, resource competition, and social behavior. – The Auk. 135: 857–867. Friedemann, G., Leshem, Y., Kerem, L., Bar-Massada, A. and Izhaki, I. 2017. Nest-site characteristics and competitive interactions between sympatric apex predators. – Ibis 159: 442–456. García, J. T. and Arroyo, B. E. 2002. Intra- and interspecific agonistic behaviour in sympatric harriers during the breeding season. – Anim. Behav. 64: 77–84. George, E. M., Weber, A. M. and Rosvall, K. A. 2024. Scope and adaptive value of modulating aggression over breeding stages in a competitive female bird – Behav. Ecol. 35: 69-75. Getty, T. 1987. Dear enemies and the prisoner’s dilemma: why should territorial neighbors form defensive coalitions? – Am. Zool. 27: 327–336. Getty, T. 1989. Are dear enemies in a war of attrition? – Anim. Behav. 37: 337–339. Ghalambor, C. K. and Martin, T. E. 2001. Fecundity-Survival Trade-Offs and Parental Risk-Taking in Birds. – Science 292: 494-7. Gladow, K.-P., Jablonski, M., Chakarov, N. and Krüger, O. 2025. Experimental comparison of defence behaviour against different avian top predators in an intraguild prey. – J. Avian Biol. : e03495. Godard, R. 1993. Tit-for-tat among neighboring territorial birds. – Behav. Ecol. Sociobiol. 33: 45–50. Hammer, Ø., Harper, D. A. T. and Ryan, P. D. 2001. PAST: Paleontological Statistics Software Package for Education and Data Analysis. – Palaeontol. Electron. 4: 1–9. Harrison, X.A., Donaldson, L., Correa-Cano, M.E., Evans, J., Fisher, D.N., Goodwin, C., Robinson, B.S., Hodgson, D.J. and Inger, R. 2018. A brief introduction to mixed effects modelling in ecology. – PeerJ 6: e4794. Heinrich, B. 1989. Ravens in winter. – Summit Books. Holthuijzen, A. M. A. and Oosterhuis, L. 2004. Aggressive responses of nesting prairie falcons. – Wilson Bull. 116: 257–261. Hsu, Y., Earley, R. L. and Wolf L. L. 2006. Modulation of aggressive behaviour by fighting experience: mechanisms and contest outcomes – Biol. Rev. 81: 33–74. Jaksić, F. M. 1985. Toward raptor community ecology. – J. Raptor Res. 19: 107–112. Jamieson, I. G. and Seymour, N. R. 1983. Inter- and intraspecific agonistic behaviour of ospreys. – Can. J. Zool. 61: 2199–2202. Jenkins, A. R. and van Zyl, A. J. 2005. Community structure of cliff-nesting raptors. – Ostrich 76: 175–184. Jiménez-Franco, M., Martinez, J.E. and Calvo, F. 2011. Territorial occupancy dynamics in a forest raptor community. – Oecologia 166: 507–516. Katsis, A. C., Common, L. K., Akçay, Ç. and Kleindorfer, S. 2025. Good guardian, bad parent: tradeoffs between territory defense and parental care in Darwin’s finches. – Behav. Ecol. 36: araf109. Kostrzewa, R. 1996. A comparative study of nest site occupancy and breeding performance as indicators for competitive interactions in raptors. – Ethol. Ecol. Evol. 8: 1–18. Krajick, K. 1999. Scientists — and climbers — discover cliff ecosystems. – Science 283: 1623–1624. Krüger, O. 2002. Interactions between common buzzard and goshawk. – Oikos 96: 441–452. Lardelli, R., Bogliani, G., Brichetti, P., Caprio, E., Celada, C., Conca, G., Fraticelli, F., Gustin, M., Janni, O., Pedrini, P., Puglisi, L., Rubolini, D., Ruggieri, L., Spina, F., Tinarelli, R., Calvi, G. and Brambilla, M. 2022. Atlante degli Uccelli nidificanti in Italia. – Edizioni Belvedere. Leyequién, E., de Boer, W.F. and Cleef, A. 2007. Influence of body size on coexistence of bird species. – Ecol. Res. 22: 735–741. Lo Valvo, M., Massa, B. and Sarà, M. 1993. Uccelli e paesaggio in Sicilia alle soglie del terzo millennio. – Nat. Sicil. 17: 1–375. Martínez, J.E., Martínez, H.A., Zuberogoitia, I., Zabala, J., Redpath, S.M. and Calvo, J.F. 2008. The effect of inter- and intraspecific interactions on the large-scale distribution of cliff-nesting raptors. – Ornis Fenn. 85: 13–21. Martínez-Hesterkamp, S., Rebollo, S., Kennedy, P.L., Pérez-Camacho, L., García-Salgado, G. and Molares-Castilla, I. 2018. Territoriality in diurnal raptors. – Biol. J. Linn. Soc. 124: 126–137. Mascara, R. 2017. Distribuzione e status riproduttivo del Corvo imperiale Corvus corax nella Sicilia centro-meridionale. – Uccelli d’Italia 42: 56–59. Maynard Smith, J. 1982. Evolution and the theory of games. – Cambridge Univ. Press. Maynard Smith, J. and Parker, G. A. 1976. The logic of asymmetric contests. – Anim. Behav. 24: 159–175. Mengoni C., Zuberogoitia I., Mucci N., Boano G., Urban T., Guzzo E., Sarà M., 2018. Genetic variability in Peregrine Falcon populations of the Western Palaearctic region. – Ornis Hungarica 26: 12–26. Montgomerie, R. D. and Weatherhead, P. J. 1988. Risks and rewards of nest defence. – Q. Rev. Biol. 63: 167–187. Mooney, N. J. and Brothers, N. P. 1987. The Peregrine Falcon Falco peregrinus macropus in Tasmania. I. Distribution, abundance and physical characteristics of nests. – Aust. Wildl. Res. 14: 81–93. Morrison, J. L., Terry, M. and Kennedy, P. L. 2006. Potential factors influencing nest defense in diurnal North American raptors. – J. Raptor Res. 40: 98–110. Müller, C. A. and Manser, M. B. 2007. ‘Nasty neighbours’ rather than ‘dear enemies’ in a social carnivore. – Proc. R. Soc. B 274: 959–965. Newton, I. 1979. Population ecology of raptors. – T. and A. D. Poyser. Newton, I. 1998. Population limitation in birds. Academic Press, California. Olendorf, R., Getty, T. and Scribner, K. 2004. Cooperative defense in territorial birds. – Behav. Ecol. 15: 910–917. Orians, G. H. and Willson, M. F. 1964. Interspecific territories of birds. – Ecology. 45: 736–745. Peiman, K. S. and Robinson, B. W. 2010. Ecology and evolution of resource-related heterospecific aggression. – Q. Rev. Biol. 85: 133–158. Ratcliffe, D. A. 1993. The Peregrine Falcon. – T. and A. D. Poyser. Ratcliffe D.A. 1997. The Raven a Natural History in Britain and Ireland. T. and A. D. Poyser. Redondo, T. and Carranza, J. 1989. Offspring reproductive value and nest defence. – Behav. Ecol. Sociobiol. 25: 369–378. Rodríguez, B., Rodríguez, A., Siverio, F. and Siverio, M. 2017. Factors affecting the spatial distribution and breeding habitat of an insular cliff-nesting raptor community. – Curr. Zool. :1–9. Salvo, G. 2015. Biologia del corvo imperiale Corvus corax in Sicilia. – Riv. Ital. Orn. 85: 41–42. Sarà, M., Mascara, R., Nardo, A. and Zanca, L. 2023. Climate effects on breeding phenology of Peregrine and Lanner Falcons in the Mediterranean. – Ardea 110: 145-159. Schielzeth H. 2010. Simple means to improve the interpretability of regression coefficients. Met. Ecol. Evol. 1:103–113. Sergio, F., and Hiraldo, F. 2008. Intraguild predation in raptor assemblages: a review. – Ibis 150: 132–145. Sergio, F., Marchesi, L., Pedrini, P. and Penteriani, V. 2007. Coexistence of a generalist owl with its intraguild predator. – Anim. Behav. 74: 1607–1616. Sergio, F., Rizzolli, F., Marchesi, L. and Pedrini, P. 2004. Peregrine Falcons seek proximity to Raven nests. – Ecography 27: 818–826. Sofaer, H.R., Sillett T. S., Peluc, S. I., Morrison, S. A. and Ghalambor, C. K. 2013. Differential effects of food availability and nest predation risk on avian reproductive strategies. – Behav. Ecol. 24: 698–707. Stamps, J. A. and Groothuis, T. G. G. 2010. Developmental perspectives on personality. – Philos. Trans. R. Soc. B 365: 4029–4041. Stamps, J. A. and Krishnan, V. V. 2001. How territorial animals compete for divisible space. – Am. Nat. 157: 154–169. Temeles, E. J. 1990. Northern harriers respond more aggressively to neighbours. – Behav. Ecol. Sociobiol. 26: 57–63. Temeles, E. J. 1994. The role of neighbours in territorial systems. – Anim. Behav. 47: 339–350. Temeles, E. J. and Wellicome, T. I. 1992. Weather-dependent kleptoparasitism and aggression in a raptor guild. – Auk 109: 920–923. West-Eberhard, M. J. 2003. Developmental plasticity and evolution. – Oxford Univ. Press. White, C. M., Cade, T. J. and Enderson, J. H. 2013. Peregrine Falcons of the world. – Lynx Edicions. Wiącek, J. 2006. Aggressive behaviour in Montagu’s harrier Circus pygargus during the courtship period. – Biologia 61: 593–595. Wiens, J. A. 1989. The ecology of bird communities. – Cambridge Univ. Press. Wilson, E. O. 1975 Sociobiology: the new synthesis. Harvard Univ. Press. Wilson, M. W., Balmer, D. E., Jones, K., King, V. A., Raw, D., Rollie, C. J., Rooney, E., Ruddock, M., Smith, G. D., Stevenson A., Stirling-Aird, P. K., Wernham, C. V., Weston, J. M. and Noble, D. G. 2018. The breeding population of Peregrine Falcon Falco peregrinus in the United Kingdom, Isle of Man and Channel Islands in 2014. – Bird Study. 65:1-19. Wingfield, J. C., Hegner, R. E., Dufty, A. M. and Ball, G. F. 1990. The ’challenge hypothesis’: Theoretical implications for patterns of testosterone secretion, mating systems and breeding strategies. – American Nat. 136: 829–846. Ydenberg, R. C., Giraldeau, L. A. and Falls, J. B. 1988. Neighbors, strangers, and the asymmetric war of attrition. – Anim. Behav. 36: 343–347. Zabala, J. and Zuberogoitia, I. 2015. Breeding performance and survival in the peregrine falcon Falco peregrinus support an age-related competence improvement hypothesis mediated via an age threshold. – J. Avian Biol. 45:141–150. Zuberogoitia, I. 2023. El Halcón Peregrino. – Tundra Ediciones. Figure Captions Fig. 1. Effects of nearest‐neighbour distance to falcons (NND falcon) on the predicted number of aggressive actions. On the left panel, the main effect of NND falcon on aggressive actions. On the right panel, the interaction between NND falcon and striker identity, disentangling the different responses among peregrine falcons, common ravens, and other species. Shaded areas represent 95% confidence intervals around model predictions. Fig. 2. Interactive effect of cliff length (L_cliff) and nearest‐neighbour distance to falcons (NND falcon) on the predicted number of aggressive actions across different levels (mean ± 1 SD)of cliff length. Shaded areas represent 95% confidence intervals around model predictions. Fig. 3. Predicted number of aggressive actions (mean ± SE) as a function of striker and recipient identity, illustrating species‐specific interaction asymmetries. Fig. 4. Interaction between striker identity and recipient status (neighbour vs intruder) on the predicted number of aggressive actions (mean ± SE). Fig. 5. Predicted number of aggressive actions (mean ± SE) across breeding stages derived from negative binomial GLMs. Peregrine falcon(left); common raven (right). Fig. 6. Seasonal variation in predicted aggressive interaction intensity derived from negative binomial GLMs. Left peregrine falcon, right common raven. Solid lines indicate predicted values, and shaded areas represent 95% confidence intervals. Vertical dashed lines mark the minimum (in A) and maximum (in B) predicted values within the observed period. Fig. 1. Effects of nearest‐neighbour distance to falcons (NND falcon) on the predicted number of aggressive actions. On the left panel, the main effect of NND falcon on aggressive actions. On the right panel, the interaction between NND falcon and striker identity, disentangling the different responses among peregrine falcons, common ravens, and other species. Shaded areas represent 95% confidence intervals around model predictions. Fig. 2. Interactive effect of cliff length (L_cliff) and nearest‐neighbour distance to falcons (NND falcon) on the predicted number of aggressive actions across different levels (mean ± 1 SD)of cliff length. Shaded areas represent 95% confidence intervals around model predictions. Fig. 3. Predicted number of aggressive actions (mean ± SE) as a function of striker and recipient identity, illustrating species‐specific interaction asymmetries. Fig. 4. Interaction between striker identity and recipient status (neighbour vs intruder) on the predicted number of aggressive actions (mean ± SE). Fig. 5. Predicted number of aggressive actions (mean ± SE) across breeding stages derived from negative binomial GLMs. Peregrine falcon(left); common raven (right). Fig. 6. Seasonal variation in predicted aggressive interaction intensity derived from negative binomial GLMs. Left peregrine falcon, right common raven. Solid lines indicate predicted values, and shaded areas represent 95% confidence intervals. Vertical dashed lines mark the minimum (in A) and maximum (in B) predicted values within the observed period. Electronic Supplementary material Fig. S1 ESM. Relationship between the number of sampled time slots and the number of aggressive activities per visit. Shaded area represents 95% confidence intervals around model prediction. Fig. S2 ESM . Predicted relationship between the number of aggressive actions and the nearest-neighbor distance (NND) to the falcon, shown across different levels of common raven NND (mean ± 1 SD). Shaded areas represent 95% confidence intervals around model predictions. Table S1 ESM. Summary of aggressive interactions (attacking and/or mobbing) between striker and recipient species. For each striker–recipient species pair, the table reports recipient phenology and status identity (intruder or neighbour), along with the recorded number of activities and number and mean (± SD) of actions. Identity Common name Scientific name Common name Scientific name Recipient Phenology Recipient identity Status identity N N Mean SD Other Common kestrel Falco tinnunculus Common raven Corvus corax resident breeder Raven intruder 1 4 4.00 Common raven Corvus corax resident breeder Raven neighbour 9 31 3.44 3.84 Eurasian buzzard Buteo buteo resident breeder Other intruder 2 5 2.50 2.12 Eurasian buzzard Buteo buteo resident breeder Other neighbour 6 20 3.33 2.58 Peregrine falcon Falco peregrinus resident breeder Peregrine neighbour 3 12 4.00 2.65 Eurasian buzzard Buteo buteo Common raven Corvus corax resident breeder Raven intruder 1 5 5.00 Peregrine falcon Falco peregrinus resident breeder Peregrine intruder 1 5 5.00 Yellow-legged gull Larus michaellis resident breeder Other intruder 1 3 3.00 Lanner falcon Falco biarmicus resident breeder Other neighbour 1 5 5.00 Eurasian jackdaw Corvus monedula Eurasian buzzard Buteo buteo resident breeder Other intruder 2 2 1.00 0.00 Common raven Corvus corax resident breeder Raven neighbour 4 23 5.75 3.10 Hooded crow Corvus cornix Eurasian buzzard Buteo buteo resident breeder Other intruder 5 11 2.20 0.84 Common raven Corvus corax resident breeder Raven neighbour 1 1 1.00 Lanner falcon Falco biarmicus Peregrine falcon Falco peregrinus resident breeder Peregrine intruder 2 19 9.50 9.19 Common raven Corvus corax resident breeder Raven intruder 1 3 3.00 Common raven Corvus corax resident breeder Raven neighbour 4 9 2.25 1.89 Eurasian buzzard Buteo buteo resident breeder Other neighbour 3 31 10.33 10.69 Lesser kestrel Falco naumanni European honey buzzard Pernis apivorus passage migrant Other intruder 1 1 1.00 Common raven Corvus corax resident breeder Raven neighbour 6 28 4.67 4.84 Eurasian buzzard Buteo buteo resident breeder Other neighbour 1 2 2.00 Lanner falcon Falco biarmicus resident breeder Other neighbour 7 13 1.86 0.90 Peregrine Peregrine falcon Falco peregrinus Black kite Milvus milvus wintering, passage migrant Other intruder 5 10 2.00 1.73 Booted eagle Aquila pennata wintering, passage migrant Other intruder 3 6 2.00 1.00 Common raven Corvus corax resident breeder Raven intruder 14 74 5.29 3.50 Egyptian vulture Neophron percnopterus summer breeder Other intruder 1 2 2.00 Eurasian buzzard Buteo buteo resident breeder Other intruder 36 124 3.44 4.06 Eurasian hobby Falco subbuteo passage migrant Other intruder 1 1 1.00 European honey buzzard Pernis apivorus passage migrant Other intruder 2 4 2.00 1.41 Golden eagle Aquila chrysaetos resident breeder Other intruder 3 16 5.33 4.04 Lanner falcon Falco biarmicus resident breeder Other intruder 3 21 7.00 9.54 large falcon Falco peregrinus cfr. calidus wintering, passage migrant Other intruder 2 12 6.00 1.41 Peregrine falcon Falco peregrinus resident breeder Peregrine intruder 12 29 2.42 2.94 Western marsh harrier Circus aeruginosus wintering, passage migrant Other intruder 1 1 1.00 Bonelli’s eagle Aquila fasciata resident breeder Other neighbour 2 5 2.50 2.12 Common kestrel Falco tinnunculus resident breeder Other neighbour 1 1 1.00 Common raven Corvus corax resident breeder Raven neighbour 58 201 3.47 3.73 Eurasian buzzard Buteo buteo resident breeder Other neighbour 12 37 3.08 2.43 Golden eagle Aquila chrysaetos resident breeder Other neighbour 1 3 3.00 Lanner falcon Falco biarmicus resident breeder Other neighbour 6 17 2.83 3.60 Lesser kestrel Falco naumanni summer breeder Other neighbour 2 3 1.50 0.71 Peregrine falcon Falco peregrinus resident breeder Peregrine neighbour 4 13 3.25 1.26 Yellow-legged gull Larus michaellis resident breeder Other neighbour 4 4 1.00 0.00 Raven Common raven Corvus corax Black kite Milvus milvus wintering, passage migrant Other intruder 5 14 2.80 1.64 Common raven Corvus corax resident breeder Raven intruder 5 22 4.40 3.71 Eurasian buzzard Buteo buteo resident breeder Other intruder 19 78 4.11 3.48 European honey buzzard Pernis apivorus passage migrant Other intruder 3 13 4.33 4.93 Golden eagle Aquila chrysaetos resident breeder Other intruder 3 15 5.00 4.58 Peregrine falcon Falco peregrinus resident breeder Peregrine intruder 1 1 1.00 Yellow-legged gull Larus michaellis resident breeder Other intruder 1 1 1.00 Bonelli’s eagle Aquila fasciata resident breeder Other neighbour 2 33 16.50 2.12 Common kestrel Falco tinnunculus resident breeder Other neighbour 3 13 4.33 3.21 Eurasian buzzard Buteo buteo resident breeder Other neighbour 8 28 3.50 2.00 Eurasian jackdaw Corvus monedula resident breeder Other neighbour 1 1 1.00 Lanner falcon Falco biarmicus resident breeder Other neighbour 2 3 1.50 0.71 Peregrine falcon Falco peregrinus resident breeder Peregrine neighbour 11 18 1.64 0.81 299 1057 3.54 3.67 Information & Authors Information Version history V1 Version 1 12 January 2026 Copyright This work is licensed under a Non Exclusive No Reuse License. Keywords agonistic behaviour cliff-nesting raptors common raven mediterranean islands peregrine falcon territoriality Authors Affiliations Maurizio Sarà 0000-0003-4274-422X [email protected] Water Research Institute National Research Council Brugherio Branch View all articles by this author Laura Zanca Private Researcher View all articles by this author Metrics & Citations Metrics Article Usage 319 views 69 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Maurizio Sarà, Laura Zanca. Agonistic behaviour of Mediterranean Peregrine Falcons during the breeding season: defending cliff territories from intruders. Authorea . 12 January 2026. DOI: https://doi.org/10.22541/au.176826080.07970791/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download. 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