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Raptors are exposed to a wide variety of human-related mortality agents, and yet population-level effects are rarely quantified. Doing so requires modeling vital rates in the context of species life-history, behavior, and population dynamics theory. In this paper, we explore the details of such an analysis by focusing on the demography of a residen...
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Collisions of large soaring raptors with wind turbines and other infrastructures represent a growing conservation concern. We describe a way to leverage knowledge about raptor soaring behaviour to forecast the probability that raptors fly in the rotor‐swept zone. Soaring raptors are theoretically expected to select energy sources (uplift) optimally...
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... obs.). However, it is currently well established that the high occurrence of territorial non-adult eagles in traditional breeding territories is a sign of high unnatural mortality and population decline (Balbontín et al. 2003, Whitfield et al. 2004a, Hunt et al. 2017). In such populations, non-adults act as a replacement for dead pair members (Carrete et al. 2006) and their high occurrence generally indicates that the adult non-territorial (floater) part of the population cannot sustain the mortality of territorial birds (Sánchez-Zapata et al. 2000, Margalida et al. 2008a). ...
... Ethiopia -Bale Mountain 100 100 Clouet et al. (1999) more than non-adult males (36:19) and a higher incidence of non-adult females in territorial pairs has been found in other studies. In Alaska, of eight territories with mixed aged pairs, all of the younger birds were females (Kochert et al. 2002), while in a population suffering from anthropogenic mortality, 13 of the 15 subadults in a population were females (Hunt et al. 2017). Adding to the bias, inexperienced raptors may produce more individuals of the smaller and "cheaper" male sex (Ferrer et al. 2009, 2013, Rosenfield et al. 2015, Morandini et al. 2020, Warkentin et al. 2022. ...
... Given the ongoing decline, alarming age structure and adult sex ratio and very low breeding success, the golden eagle population in the country most probably operates as a sink for the Balkan population (Katzner et al. 2017, Hunt et al. 2017 and is held at levels much below the carrying capacity, but this statement needs further confirmation. Moreover, a study by means of satellite telemetry on the mortality causes of territory holders and floating non-adults and on the breeding performance is needed to inform and strengthen conservation actions (Sergio et al. 2019). ...
Generally, golden eagles have a favourable conservation status but they are threatened in some parts of their range. A nationwide breeding survey of the golden eagles in Bulgaria found that the species is in a decline. Contrary to the last estimation for 212 pairs, only 93 territories were found occupied while 81 were vacant. Only half of the pairs were in adult plumage and the other half had at least one of the members in non-adult plumage. The adult sex ratio was biased towards males (1.31 males per female), with the male older in 26 out of 33 territories, where the birds differed in their age classes. The obtained results could be explained by a very high unnatural mortality of territorial birds.
... In contrast, the same level of exposure to additional mortality risk may affect multiple non-territorial individuals using each Patch. This idea aligns with empirical data indicating that mortality due to electrocution disproportionately affects juveniles and immatures rather than adults in the Bonelli's eagle Sousa, 2017) and other birds of prey (Hunt et al., 2017;Mojica et al., 2018). From a population demography perspective, this implies that for a given level of exposure to a mortality risk source, the effective decline in the population survival rate is greater when it affects non-territorial individuals compared to territorial individuals (as confirmed by our simulations; Fig. 5a), because more non-territorial than territorial individuals tend to be exposed to the risk. ...
Wildlife anthropogenic mortality is increasing worldwide, yet there is limited understanding regarding its population level impacts. Territorial species stand out in this context, as they possess distinctive characteristics that are often overlooked but may significantly affect their vulnerability. In particular, population impacts may depend on the level and spatial distribution of additional mortality risk across territories, and on the extent to which exposure to increased mortality varies across life stages (i.e., territorial and non-territorial individuals). In this study, we developed an Individual-Based Model (IBM) to explore these issues, using the Bonelli's eagle (Aquila fasciata) and electrocution in powerline pylons as a model system. We used declines in annual population growth rates as a proxy for negative impacts, and conducted simulations to estimate the relative impacts of different levels of mortality risk, the spatial pattern of such risks, and the risk exposure of different life stages. Population level impacts greatly increased with the mortality risks simulated, and they were lower when exposure to mortality risks was concentrated versus spread across territories. Impacts were highest when both territorial and non-territorial individuals were exposed to anthropogenic mortality risks, and they were higher when such exposure only affected non-territorial versus territorial individuals. Our results underscore that each breeding territory should be considered as a unit, where all existing pylons should be intervened whenever mitigation actions are put in place. Results also highlight the importance of considering both the territorial and non-territorial fractions of the population to prevent and mitigate the impacts of increased mortality. More generally, our study illustrates the value of IBM frameworks such as ours to explore population-level impacts resulting from anthro-pogenic mortality in territorial species, and to inform the development of conservation strategies to mitigate such impacts.
... Large vultures are especially vulnerable (decreases in survival by 15-30 %, Martínez-Abraín et al., 2012;Monti et al., 2022). Territorial Egyptian vultures Neophron percnopterus (Carrete et al., 2009) and golden eagles (Grainger Hunt et al., 2017) showed no measurable decrease in survival (despite them being collision victims, i.e. Ferrer et al., 2012;Katzner et al., 2017). ...
... Beside species-specific differences, age also plays a considerable role when assessing collision risks. Although survival of territorial golden eagles were found to be unaffected, non-breeders experienced a considerable decline in survival and local populations affected by wind turbines might only be maintained by immigration (Grainger Hunt et al., 2017). Golden eagles are also globally considered a species at risk due to wind power expansions (Balotari-Chiebao et al., 2021;Diffendorfer et al., 2021;Katzner et al., 2017). ...
Wind power plays a vital role in global climate action and plans for new turbines in the Baltic Sea region are underway. However, it is crucial not to overlook the environmental impact on wildlife, which can be difficult to quantify, especially in elusive and hard-to-track species. One of these species is the white-tailed eagle, a conservation success story that faces a significant collision risk with rotor blades, particularly as turbines are being constructed in its coastal habitats. To assess the effect of wind turbines on survival of territorial adults, we genotyped DNA from adult feathers collected at nests between 2010 and 2022. By tracking individuals across years, we measured survival and breeding dispersal in relation to wind turbine presence. Turbines within a 5 km radius of nests were found to reduce annual survival rates by 7.6 %, while resighting probability and breeding dispersal probability were unaffected. The proportion of territories exposed to wind turbines is currently low (4-5 %), mainly because recent construction sites have been further inland. However, future projections suggest an increase in territory exposure, indicating potential for population-level risks. This highlights the need for substantial safety buffers around nest sites (preferably >5 km) to protect the breeding white-tailed eagle population. Currently, a comprehensive understanding of the large-scale impact on the Baltic Sea white-tailed eagle population is lacking. As wind power expands, it is necessary to consider its impact on wildlife and we recommend conducting ongoing environmental assessments to monitor and adapt conservation measures.
... While cavity nesting provides a good example of site dependence, non-cavity nesters may also be site dependent (Newton 1998:204 -209), e.g., raptors such as peregrine falcons (Falco peregrinus) (Hunt 1988;Newton 1988), northern aplomado falcons (Falco femoralis septentrionalis) (McClure et al. 2016), European red kites (Milvus milvus) (Katzenberger et al. 2021), golden eagles (Aquila chrysaetos) (Hunt 1998;Hunt et al. 2017), and Spanish imperial eagles (Aquila adalberti) (Ferrer and Donazar 1996). There are likely non-avian examples, including insects requiring an oviposition site, and cavity-nesting mammals such as the greater glider (Petauroides volans) (Strahen 1998), but I will restrict my presentation to the avian context. ...
... is not the only possibility; it reflects the demography of golden eagles, for which m = 3 (Hunt et al. 2017), but will illustrate that the equilibrium population dynamics of sitelimited populations with more than one quality of site are more subtle than might appear at first sight. An alternative is mentioned at the end of this section. ...
... For a real population, m will not be very large so the lag in production of the first cohort of maturing fledglings will not be too great and the factor most important for whether an actual founding population achieves success in establishing itself is likely n, the size of the founding population. For example, the vital rates, with anthropogenic mortality censored, of the golden eagle population of Hunt et al. (2017) are: m = 3; f A = 0.2313 (female fledglings per pair); σ 1 = 0.893; σ 2 = σ 3 = σ 4 = 0.978; σ A = 0.935, R 0 = 2.78. Simulation 1 (all simulations, i.e., numerical instances of the models, are displayed in Supplement.xlsx, with additional text in Supplement.pdf) provides an example of how a population increases with this regime of vital rates when sites are unlimited in number. ...
Adults of site-dependent species require a discrete structure, e.g., a cavity, for breeding, which they are unable to construct and must locate and occupy. The environment provides only a limited number of such sites, which may vary in overall quality due to their environmental context. Heterogeneity of site quality can result in population equilibrium, often construed as source-sink dynamics. Rodenhouse et al. (Ecology 78:2025-2042, 1997) proposed a mechanism of site-dependent equilibrium that they claimed was more general than source-sink dynamics. After defining notions of source and sink, I use explicit dynamical models for a site-dependent population, based on the life history of golden eagles (Aquila chrysaetos), with two levels of site quality, to investigate the existence of population equilibria under several scenarios: source-source, source-sink, and source-floater. The life history traits I employ are not overly restrictive and serve the purpose only of providing models explicit enough to be treated analytically. I use a generalized notion of “golden eagle” since site dependency is often discussed in the literature on raptors, and I have exploited details from Hunt et al. (PLoS ONE 12:e0172232, 2017) for numerical simulations. The crucial features of the modeling, however, are those of site dependency. The modeling emphasizes that equilibrium results from the limited supply of source sites and that vital rates averaged across site qualities do not provide a compelling explanation of equilibria, contra Rodenhouse et al. Counterintuitively, equilibria are theoretically possible, even when both site qualities are intrinsically source sites.
... Although the current population and nesting status of Golden Eagle has been widely studied in the United States of America (Hunt et al., 2017;Millsap et al., 2015;Nielson et al., 2017;U.S.F.W.S., 2016), very little is known for northern Mexico (Bravo-Vinaja et al., 2015;De León-Girón et al., 2016;Flesh et al., 2020;Rodríguez-Estrella et al., 1991;Rodríguez-Estrella et al., 2020). In northwestern Baja California, a total of 39 individuals were recorded during an aerial census in 2015, including 9 nesting territories (De León-Girón et al., 2016), indicating one of Mexico's highest potential regions for nesting and conservation of Golden Eagle (De León-Girón et al., 2016;Rodríguez-Estrella et al., 2020;Tracey et al., 2018;. ...
Revista Mexicana de Biodiversidad 95 (2024): e955247 Ecology Aerial identification and quantification of nesting sites of Golden Eagle (Aquila chrysaetos) in the mountain ranges of central Baja California Peninsula, Mexico Identificación y cuantificación aérea de sitios de anidación de águila real (Aquila chrysaetos) en las montañas del centro de la península de Baja California, México Abstract Aerial census for identification and quantification of nesting sites of Golden Eagle was performed through the mountain ranges of the central Baja California Peninsula, Mexico from 5 to 8 April 2021. We identified a total of 113 nests and 12 territories of Golden Eagle on a sampling trajectory of 1,203 km that encompassed a surface of 176,000 ha. The highest abundance of nests (n = 57) was recorded between 29º and 30º N latitudes with elevations ranging between 600 and 700 m (n = 35) in the Valle de Los Cirios Protected Natural Area, which is mainly associated with mountain biotopes with steep cliffs and ample alluvial valleys that promote foraging and nesting sites for this species. The number of nests of Golden Eagle showed an inverse relationship with the altitude along a latitudinal gradient. This study reports new nesting sites of Golden Eagle in the central peninsular region that includes the mountain ranges of Matomí, Jaraguay, and La Libertad.
... In our study system, the demonstrable potential adverse impact is markedly towards functional habitat loss. In other study systems where eagles are apparently less wary of turbines, and hence where collision with turbine blades is more likely [8,18,21,25,34,36,37,75], the same considerations on the attractiveness of underlying turbine locations and their surroundings should also apply in generating a potentially adverse impact. Even if that impact may differ because of differences in birds' wariness of turbines and the more likely underlying effect [13][14][15]. ...
Understanding drivers underlying birds’ responses to operational wind turbines is essential for robust wind farm proposal assessments, especially for large raptors with life history traits engendering sensitivity to impacts from two potential adverse effects: fatality through collision with rotating turbine blades and functional habitat loss through avoidance of turbines. The balance between these two potential effects represents opposing extremes on a continuum and is influenced by several factors. Collisions have an obvious impact on survival, but the impacts of avoidance may be more insidious and potentially more significant for a population. It is reasonable to conclude that collisions are less likely when blades are motionless. Consequently, turbine shutdown systems (TSSs, “shutdown on demand” or “curtailment”), instigated as raptors approach operational turbines, may provide mitigation against collisions. By contrast, if avoidance is most likely, this could be independent of blade motion, and TSSs/curtailment would provide no mitigation against habitat loss. For birds tending to wariness of turbines, therefore, it is important to understand if it is conditional on blade motion. Scottish golden eagles show a strong propensity to avoid (be wary of) turbines, subject largely to the suitability of habitat at and surrounding turbine locations. A previous Scottish study found that approach distances to turbines by non-territorial eagles were unaffected by blade motion but were closer at higher wind speed. Here, we analyse movement data from a GPS-tagged territorial eagle and non-territorial eagles responding to the motion status (and wind speed) of turbines at another Scottish wind farm. Eagles’ approach distances to turbines were only weakly affected by blade motion but were closer at higher wind speed. We again found that habitat suitability in and around turbine locations was strongly influential on eagles’ approach distance to turbines. Our confirmation that blade motion had little effect on Scottish golden eagles’ wariness of turbines suggests that for eagles that are prone to avoid turbines, their wariness is a response to turbines per se, and not blades’ movement. In our study system, and others where avoidance is the predominant response, curtailment of turbines’ operation on birds’ close approaches, or making turbine blades more obvious, should, therefore, have little material influence on functional habitat loss impacts. If true, this has important implications for wind farm designs and any proposed mitigation.
... Large soaring raptors, characterized by a low aerial maneuverability and a reduced frontal vision (Martin et al., 2013), are particularly prone to collide with rotating blades when turbines occur on areas regularly used by resident individuals (Fielding et al., 2021;Martín et al., 2018), such as foraging grounds (Katzner et al., 2012), slopes generating updrafts (Péron et al., 2017) or roosts (Carrete et al., 2012). For many species, collisions with blades can become a relevant source of J o u r n a l P r e -p r o o f mortality (Bellebaum et al., 2013;Grainger Hunt et al., 2017) capable of jeopardizing endangered populations (Carrete et al., 2009;Cervantes et al., 2022). This is the case for many Old World Vultures for which collision with wind turbines is considered a main threat (Ives et al., 2022). ...
Griffon vulture (Gyps fulvus) populations occur on Mediterranean islands, where wind energy is developing fast. As griffons are subjected to collisions with wind turbines while foraging, it is necessary to understand which factors affect their movements to minimize the potential impact of wind farms.
We assessed habitat use of 37 griffons (n. GPS locations = 130,218) and their overlap with wind farms in Sardinia (Italy), an island where both griffon vulture population and wind energy are significantly expanding.
Griffons in Sardinia cover smaller areas (95% isopleth = 956.3 ± 677.7 km2, 50% isopleth = 73.8 ± 48.2 km2) than in mainland Europe, restricting most of their movements within 5-10 km from colonies and roosts. Supplementary feeding stations throughout these areas (n = 37) provide approximately 20 tons of carrion each year, suggesting that griffon movements are strongly determined by food availability.
Overall, 6 wind farms (101 turbines) out of the 29 present in Sardinia were built in areas used by foraging griffons. Two of them were positioned near roosts and supplementary feeding stations. As griffon movements concentrate around nesting/roosting sites and feeding stations, wind farms should be excluded around these highly utilized areas, and mitigation measures, including the removal of livestock carrion, should be adopted for those that are built at greater distances. There is also an urgent need for updated data about wind energy location. The creation of supplementary feeding stations could be used to shape the enlargement of the foraging grounds of an increasing Griffon Vulture population on Mediterranean islands and to exclude wind farm areas to mitigate their impacts.
... Large raptors also possess life history traits sensitive to additive mortality from anthropogenic sources [20][21][22], notably in older individuals [7,[23][24][25][26][27][28]. Alarms have been raised on collision mortality potentially affecting population viability in several species [28][29][30][31][32][33]. ...
... Large raptors also possess life history traits sensitive to additive mortality from anthropogenic sources [20][21][22], notably in older individuals [7,[23][24][25][26][27][28]. Alarms have been raised on collision mortality potentially affecting population viability in several species [28][29][30][31][32][33]. ...
... The golden eagle Aquila chrysaetos is well-studied in wind farm research. In North America, the consensus is that both non-territorial and territorial birds are mostly vulnerable to collision and consequent fatalities [7,14,15,18,19,28,49,50]. Avoidance may be more likely in migrating eagles [42] through the use of different sources of wind energy uplift to some resident birds [51,52]. ...
Research on potentially adverse effects of wind farms is an expanding field of study and often focuses on large raptors, such as golden eagles, largely because of their life history traits and extensive habitat requirements. These features render them sensitive to either fatality (collision with turbine blades) or functional habitat loss (avoidance through wariness of turbines). Simplistically, avoidance is antagonistic to collision; although, the two processes are not necessarily mutually exclusive in risk. A bird that does not enter a wind farm or avoids flying close to turbines cannot collide with a blade and be killed. In the USA, collision fatality is implicated as the typical adverse effect. In Scotland, avoidance of functional habitat loss appears more likely, but this depends in part on the habitat suitability of turbine locations. Previous Scottish studies have largely concentrated on the responses of GPS-tagged non-territorial golden eagles during dispersal. Several arguments predict that territorial eagles may have lower avoidance (be less wary) of turbines than non-territorial birds. Hence, we contrasted the responses of GPS-tagged non-territorial (intruding) and territorial eagles to the same turbines at 11 operational Scottish wind farms. We show that territorial eagles rarely approached turbines, but, as in previous Scottish studies of non-territorial birds, the spatial extent of avoidance depended on the habitat suitability of both turbine locations and their wider surroundings. Unexpectedly, we found that territorial eagles were apparently as wary as intruding non-territorial conspecifics of the same turbines. Our results show that regardless of age or territorial status, Scottish golden eagles largely avoided wind turbine locations, but this avoidance was conditional, in part, on where those turbines were located. Responses to turbines were also strongly dependent on birds’ identities and different wind farms. We speculate on how widespread our findings of avoidance of turbines by golden eagles are elsewhere in Europe, where there appear to be no published studies showing the level of collision fatalities documented in the USA.
... A stochastic population matrix model developed by Monzón and Friedenberg (2018) explored the floater dynamics of Moffat's equilibrium (Hunt 1998, Hunt et al. 2017. Importantly, the rate of floater transition to the breeder stage was modeled dynamically so that transitions were determined by the availability of territories. ...
... High rates of subadult occupancy manifested in both increasing and declining populations. In all, we found Monzón and Friedenberg's (2018) modeling results consistent with Moffat's equilibrium dynamics as described by Hunt (1998), Hunt and Law (2000), and Hunt et al. (2017). ...
... A practical consideration regarding the floater-tobreeder ratio is whether, outside of a modeling context, it would ever be considered a snapshot, given the difficulty of measuring it. Doing so under normal circumstances requires its computation through an analysis of the vital-rate regime (see Hunt et al. 2017). A direct count is conceivable, as in the rare case of a small, closed, exposed population (Komdeur 1996), but even then, the floater-tobreeder ratio is not really a snapshot, considering the additional information that surfaces during the count. ...
... This behaviour had not been recorded before for soaring birds. We found no effects of bird's age or sex on flight directions despite several studies reporting sex and age differences in turbine collision rates of soaring birds [26][27][28][29] . Our results are consistent with those published earlier for this species showing that utilization distribution around wind turbines is not influenced by age or sex 13 . ...
Wind energy production has expanded as an alternative to carbon emitting fossil fuels, but is causing impacts on wildlife that need to be addressed. Soaring birds show concerning rates of collision with turbine rotor blades and losses of critical habitat. However, how these birds interact with wind turbines is poorly understood. We analyzed high-frequency GPS tracking data of 126 black kites (Milvus migrans) moving near wind turbines to identify behavioural mechanisms of turbine avoidance and their interaction with environmental variables. Birds flying within 1000 m from turbines and below the height of rotor blades were less likely to be oriented towards turbines than expected by chance, this pattern being more striking at distances less than 750 m. Within the range of 750 m, birds showed stronger avoidance when pushed by the wind in the direction of the turbines. Birds flying above the turbines did not change flight directions with turbine proximity. Sex and age of birds, uplift conditions and turbine height, showed no effect on flight directions although these factors have been pointed as important drivers of turbine collision by soaring birds. Our findings suggest that migrating black kites recognize the presence of wind turbines and behave in a way to avoid then. This may explain why this species presents lower collision rates with wind turbines than other soaring birds. Future studies should clarify if turbine avoidance behaviour is common to other soaring birds, particularly those that are facing high fatality rates due to collision.
