A comprehensive analysis of spatial and temporal patterns of anthropogenic adult mortality of Bonelli's eagles in eastern Spain
Abstract
In eastern Spain, Bonelli's eagle (Aquila fasciata) abundance has declined almost 50% in the last 25 years and, consequently, the species is listed as regionally endangered. Therefore, the aim of this study is to report the mortality causes of territorial breeding Bonelli's eagles, including the spatial and temporal patterns, and to assess the effects on population dynamics. From 2015–2023, we tracked 60 Bonelli's eagles via global positioning system-global system for mobile communications (GPS-GSM) telemetry; 33 of the eagles died (median survival time = 1,519 days). Survival did not differ in relation to sex, age at capture (subadult vs. adult birds), breeding site (coastland vs. inland territories), or transmitter's model. One-year probability of survival (95% CI) was 0.716 (0.607–0.845); 2-year survival was 0.640 (0.524–0.781); and 3-year survival was 0.581 (0.464–0.729). Anthropogenic mortality (66.7% of cases) prevailed over natural (27.3%) and unknown causes (6.0%). Causes of mortality were intra- and interspecific predation (24.2% of cases), electrocution (18.2%), poisoning (15.1%), collision with power lines (9.1%), shooting (9.1%), drowning (9.1%), collision with other man-made infrastructure (6.1%), and disease (3.0%). Deaths were most frequent during the early breeding season. Only 2 (6.1%) of 33 deaths recorded occurred within a protected area. Natural causes of mortality were more frequent away from the Mediterranean coast. In contrast, anthropogenic deaths were more frequent near the Mediterranean coast, where human population density is high. We estimated that probability of extirpation of the species in our study area is 17.8% in the next 50 years and 99.2% in 100 years. Nonetheless, a small reduction in adult mortality by ≥15% could prevent extirpation in the next 50 years. Therefore, actions to reduce adult mortality are urgently needed to preserve the Bonelli's eagle in eastern Spain.
INTRODUCTION
Apex predators including diurnal raptors and owls (Falconiformes, Accipitriformes, Strigiformes) tend to be species that are most vulnerable to anthropogenic threats (Owens and Bennett 2000, Sergio et al. 2008, McClure et al. 2018, Buechley et al. 2019). Raptor populations are facing many anthropogenic threats, such as habitat loss, habitat degradation and fragmentation, direct persecution, poisoning, and electrocution (González et al. 2007, Hager 2009, Boal and Dykstra 2018, Al Zoubi et al. 2020, Biasotto et al. 2022), among others. Population stability of long-lived raptors, in particular, is sensitive to adult survival (Sutherland 1996, Sæther and Bakke 2000, Crone 2001); elevated mortality among adults increases the rate of territorial abandonment, which provides an early warning signal of population decline (Carrete et al. 2002, Ferrer et al. 2003).
Accurately estimating rates of mortality attributed to various causes is essential for mitigating threats and thus recovering threatened populations of wildlife (Crouse et al. 1987, Ferrer and Calderón 1990, Hiraldo et al. 1996, Fujiwara and Caswell 2001, Sergio et al. 2019). Nonetheless, most estimates of wildlife survival and mortality have been based on capture-mark-recapture models that require re-sighting of marked animals, which have important limitations to know precisely when, where, and how mortality occurs (Marra et al. 2015).
In Mediterranean ecosystems, the Bonelli's eagle (Aquila fasciata) is a long-lived, apex predator (Cramp and Brooks 1992, Ontiveros et al. 2004). The eagle's abundance has decreased in the Iberian Peninsula in recent years (Del Moral and Molina 2018). Some small subpopulations became extirpated, and others are in decline, especially in Aragón, País Vasco, La Rioja, Navarra, Castilla y León, and Castilla-La Mancha regions within inland Spain (Del Moral and Molina 2018). The Bonelli's eagle has a source-sink metapopulation dynamic in the Iberian Peninsula (Soutullo et al. 2008, Hernández-Matías et al. 2013), with the metapopulation declining in size and range. In particular, breeding performance and territory occupancy of the eagle diminish towards northwestern portions of the peninsula (Ontiveros and Pleguezuelos 2000, López-López et al. 2007a, Carrascal and Seoane 2009, López-Peinado and López-López 2023). This seems consistent with the melting range analogy (Rodríguez 2002), that bird species are more likely to lose territories at the periphery of their breeding ranges (Krüger et al. 2014).
In this context, in 2000 we began to document the breeding ecology and long-term population dynamics of the Bonelli's eagle in the eastern portion of the Iberian Peninsula, to further conservation of the species (López-Peinado and López-López 2023). Population models already had begun to support management decisions for the eagle in other parts of its breeding range across Mediterranean countries (Real and Mañosa 1997, Carrete et al. 2002, Rollan et al. 2021). In 2015, we began to track Bonelli's eagles in this eastern population via global positioning system-global system for mobile communications (GPS-GSM) telemetry because knowledge of limiting factors was poor. Our objectives were to understand mortality causes, their determinants, and evaluate their effects on this subpopulation at a regional level. Furthermore, our ultimate goal was to provide recommendations for conservation actions to mitigate mortality risks and to increase the viability of Bonelli's eagle populations in eastern Spain.
STUDY AREA
Our study area encompasses the Valencian Community and the eastern part of Cuenca and Albacete provinces of eastern Spain (Castilla—La Mancha region). This Mediterranean region includes elevations from sea level to 1,814 m above sea level, with abrupt changes in terrain ruggedness associated with mountain ranges across the region that provides suitable nesting habitat for Bonelli's eagles. Mean annual temperature varies from 17°C at lower and coastal areas to 8°C at the inland mountains. Annual mean precipitation varies from 400–900 mm, with highest values during autumn and spring and the lowest during summer. During our study, land cover was oak (Quercus spp.) and pine (Pinus spp.) forests and shrublands intermingled with non-irrigated and irrigated cultivation zones. Prey for the Bonelli's eagle appear to be locally abundant in some places, including mainly red-legged partridges (Alectoris rufa), pigeons (Columba spp.), European rabbits (Oryctolagus cuniculus), Iberian hares (Lepus granatensis), and lizards (Timon spp.). According to the latest regional survey, the 2022 population of Bonelli's eagle in the study area is 52-54 breeding pairs (P. López-López, University of Valencia, unpublished data).
METHODS
Telemetry data and mortality information
During 2015-2023 we used folding nets to capture Bonelli's eagles (Perona et al. 2019) on their nesting territories and fitted them with 48-g and 50-g solar-powered GPS-GSM datalogger transmitters (e-obs GmbH, Munich, Germany; Ornitela, Vilnius, Lithuania) via backpack harnesses (Kenward 2000) designed to break loose near the end of the tag's life (expected tag life ~4 years). Each transmitter recorded a GPS location every 5 minutes from 1 hour before sunrise to 1 hour after sunset, year-round (Morollón et al. 2022a). Transmitter-harness packages weighed <3% of a given eagle's mass, as recommended by Kenward (2000).
We checked each eagle's telemetry data daily for signs suggesting non-movement (e.g., clustered GPS locations or anomalies in body position indicated by accelerometry data). If such signs were evident, we immediately investigated the respective site to determine whether the eagle was dead or injured. We collected carcasses and specialized wildlife veterinarians performed necropsies. We submitted injured eagles to wildlife rehabilitation centers.
Data analysis
We fit a Cox proportional hazards model (Cox 1972) to investigate the association between the survival time of eagles (in days) and 4 predictor variables: age at capture (subadult [2–4 yr] or adult [>4 yr]), sex, tag model (48-g e-obs tags or 50-g Ornitela tags), and breeding site (coastland territory or inland territory). Then, we plotted Kaplan-Meier survival curves for each categorical variable, and we fit Cox regression models to assess simultaneously the effect of all predictors on survival time. We also computed the probability of surviving to different years during the study period.
We tested the assumptions of the Cox proportional hazards regression model (i.e., that the hazards are proportional at each point in time throughout the study period) using the cox.zph function from the survival R package and visually checked assumptions using the Schoenfeld residuals plot. We conducted all survival analyses using the survival, survminer, and ggsurvfit R packages in R version 4.3.0 (R Core Team 2020).
We estimated the probability of extirpation of Bonelli's eagles in eastern Spain by using a population viability analysis (PVA), following the approach used for Bonelli's eagles in previous works (Soutullo et al. 2008, López-López et al. 2012). We built the PVA using Vortex simulation software (Lacy and Pollak 2023). We constructed a life-history table with parameters obtained by combining data from our field surveys, telemetry work, and available literature (Table 1). With this information we ran a baseline scenario and computed the intrinsic deterministic population growth rate (rdet) and the intrinsic stochastic population growth rate (rstoc; Miller and Lacy 2005). Once we obtained these values (r), we calculated the population growth rates (λdet and λstoc) as λ = er (Caswell 2001). We performed all simulations for >50 years in 500 different iterations, and we considered the population to be virtually extirpated when individuals from only 1 sex remained alive. We calculated the probability of quasi-extirpation as the proportion of iterations that were performed before a population became extirpated after 50 simulated years. We modeled the initial population size as a stable age distribution and considered the mating system to be long-term monogamy (Ontiveros 2016), which was confirmed by our field observations and telemetry information. For the main objectives of this study, we assumed that immigration and emigration rates were equal. Although we acknowledge that this is not biologically accurate, the lack of precise information on the rates of immigration and emigration of juvenile and floating individuals in our subpopulation precluded us from incorporating sufficiently realistic scenarios that accounted for these variables. Furthermore, recent studies with this species demonstrate that population growth rates are highly sensitive to small variations in immigration and emigration rates (Badia-Boher et al. 2024). Therefore, we preferred to simulate scenarios in which immigration and emigration rates were equivalent in demographic terms. Furthermore, immigration and emigration are demographic parameters that are difficult to improve from the perspective of managing actions applied to Bonelli's eagle conservation. Based on our field observations, we did not include density-dependent effects on reproduction in the models (López-Peinado and López-López 2023). We did not include potential effects of inbreeding depression, catastrophes, harvesting, supplementation, or genetic management in the simulations.
| Parameter | Value | References |
|---|---|---|
| Number of runs (simulations) | 500 | Soutullo et al. (2008), López-López et al. (2012) |
| Number of years for projection | 50 | |
| Definition of extinction | when only 1 sex remains | Soutullo et al. (2008), López-López et al. (2012) |
| Number of populations | 1 (isolated population, immigration equals emigration) | |
| Dispersal | (not modeled) | |
| Reproductive system | Long-term monogamy | Ferguson-Lees and Christie (2001) |
| Age of first breeding (both sexes) | 3 years | López-Peinado and López-López (2023) |
| Maximum age of reproduction | 25 years | Soutullo et al. (2008), López-López et al. (2012), Ferguson-Lees and Christie (2001) |
| Maximum number of progeny per year | 2 nestlings | López-Peinado and López-López (2023) |
| Sex ratio at birth (% males) | 50% | Soutullo et al. (2008), López-López et al. (2012) |
| Density-dependent effects on reproduction | not modeled | López-Peinado and López-López (2023) |
| Mean (±SD) of percentage of females breeding | 68.69 ± 12.54, fieldwork in the study area for the period 2000–2023 (average breeding success) | López-Peinado and López-López (2023) |
| Number offspring per female per year (% in each class) | Mean of the percent of nests with ≥1 chicks according to fieldwork in the study area for the period 2000–2023 (44% 1 chick; 56% 2 chicks) | López-Peinado and López-López (2023) |
| Males in breeding pool (%) | 100% | Soutullo et al. (2008), López-López et al. (2012) |
| Initial population size (N) | 200 individuals | López-Peinado and López-López (2023) |
| Carrying capacity (K) | 500 individuals | López-Peinado and López-López (2023) |
| Harvesting | not modeled | |
| Supplementation | not modeled | |
| Mortality rates (in percentage): | ||
| from age 0 to 1: | 52.1a | Hernández-Matías et al. (2011) |
| from age 1 to 2: | 43.0a | Hernández-Matías et al. (2011) |
| from age 2 to 3: | 15.1 | Present study |
| after age 3: | 15.1 | Present study |
- a Juvenile mortality from Hernández-Matías et al. (2011) based on capture-mark-recapture methods.
To estimate population trajectories, we evaluated the probability of population extirpation (PE; the proportion of the 500 iterations in which the population became extirpated) and the expected annual rate of population growth (λ). Values of λ equal to 1 indicate that the population would remain stable; values below or above 1 indicate a population decrease or increase, respectively. Finally, to determine how changes in adult mortality affect population trends, we conducted an elasticity analysis (Caswell 2000) in which we simulated different scenarios of a 5%, 10%, 15%, and 20% decrease in adult mortality. We then compared these simulated scenarios to the baseline model. We performed simulations by varying adult mortality at a time while keeping the other parameters unchanged. We evaluated effects of changes in the elasticity analysis based on the probability of the PE and λ.
RESULTS
During May 2015–August 2023, we fitted GPS-GSM transmitters on 60 adult Bonelli's eagles at their nesting territories in the eastern portion of the Iberian Peninsula. We monitored 9–35 individuals annually (Table S1, available in Supporting Information). Transmitters on 3 Bonelli's eagles stopped functioning for no apparent reason, such that fates of the respective eagles were unknown.
Overall, 33 (55.0%) of the eagles died (median survival time = 1,519 days). The probability of survival to 1 year (95% CI) was 0.716 (0.607–0.845), 2-year survival was 0.640 (0.524–0.781), 3-year survival was 0.581 (0.464–0.729), 4-year survival was 0.523 (0.404–0.676), 5-year survival was 0.425 (0.305–0.591), and 6-year survival was 0.318 (0.190–0.535). The probability of survival for years 6–10 did not differ.
Survival rates did not differ in relation to sex, age at capture, breeding site, or transmitter model (Table 2). The Kaplan-Meier survival curves showed no significant evidence of effects of categorical variables on survival probability (all P-values > 0.05; Figure 1).
| β | HR (95% CI) | Wald test | P-value | |
|---|---|---|---|---|
| Age | 0.234 | 1.264 (0.548–2.913) | 0.550 | 0.583 |
| Sex | −0.016 | 0.984 (0.480–2.015) | −0.045 | 0.964 |
| Transmitter | 0.464 | 1.591 (0.653–3.873) | 1.023 | 0.306 |
| Site | −0.252 | 0.777 (0.337–1.800) | −0.590 | 0.555 |
Causes of death
We could determine cause of death for 31 of 33 (93.9%) Bonelli's eagles that were recovered dead. Most mortality was anthropogenic (66.7% of cases). This included electrocution (6 cases), poisoning (5 cases), collision with power lines (3 cases), collision with fences (2 cases), drowning in artificial ponds (i.e., animal and agricultural watering tanks; 3 cases), and shooting (3 cases). Mortality attributed to natural sources (27.3% of cases) included intra- and interspecific predation (8 cases) and disease (1 case). Cause of mortality in 2 cases (6.1%) was unknown.
Temporal variation
Bonelli's eagles in this study lived for an average of 672.9 days (SD = 650.4; median = 383; range = 3–2,188 days) while being tracked. Mortality events were not randomly distributed across months of the year (Figure 2; Fisher's exact test, P = 0.01). Highest monthly mortality occurred in March, totaling 9 eagle deaths compared to an average of 2.6 ± 2.4 deaths per calendar month. The temporal distribution of causes of mortality could not be distinguished from a random pattern, except for mortality due to poisoning ( = 25.6, P = 0.001). In 2018, poisoning caused the deaths 2 eagles on 21 March and 2 eagles on 29 March. In 2019, poisoning caused death of another eagle in March (Figure 2).
Month-by-month occurrence of other forms of anthropogenic mortality did not differ from that expected by chance (all P > 0.05; Figure 2). Six of 8 deaths due to predation occurred during March (2 cases) and April (4 cases), which is in the middle of the breeding season (Figure 2; = 25, P < 0.01). We did not analyze mortality from other causes because too few deaths were recorded. Only 2 (6.1%) of the Bonelli's eagle deaths occurred within a protected area even though most eagles (86%) we studied bred there (Fisher's exact test, P < 0.001; Figure 3). Moreover, in the inland areas of the eastern Iberian Peninsula, mortality associated with interspecific aggression occurred more frequently than anthropogenic mortality (Fisher's exact test, P = 0.01; Figure 3). In contrast, deaths of individuals in coastland areas were mainly due to anthropogenic mortality (Figure 3).
Population trend
Results of the PVA suggested that the Bonelli's eagle population in eastern Spain will decrease in the near future, whether considering output of a deterministic model (rdet = −0.0403) or including stochasticity in the simulations (rstoc = −0.0612 ± 0.1224). In both cases, the population growth rate (λ) was <1, indicating a population decrease (λdet = 0.9605; λstoc = 0.9406). The baseline model indicated that Bonelli's eagles in eastern Spain will be extirpated in <50 years (mean time of extirpation = 44.2 years). Considering this scenario, the PVA forecasted a 17.8% probability of extirpation in the next 50 years and 99.2% probability of extirpation in the next 100 years.
Based on our elasticity analysis, some decreases in adult mortality would reduce the risk of extirpation (Figure 4). For example, a 5% reduction in adult mortality would reduce the PE from 17.8% to 9.2% in 50 years (rdet = −0.0332; rstoc = −0.0516 ± 0.1115), a 10% reduction would decrease the PE to 2.6% (rdet = −0.0261; rstoc = −0.0412 ± 0.1003), and 15% and 20% reductions could prevent extirpation in the next 50 years (PE = 0%; 15%: rdet = −0.0192; rstoc = −0.0224 ± 0.0763, 20%: rdet = −0.0123; rstoc = −0.0229 ± 0.0841; Figure 5).
DISCUSSION
In long-lived species, exacerbated mortality of adult individuals can lead to population decline and extinction (Sutherland 1996, Sæther and Bakke 2000, Crone 2001). To conserve such species, the potential effects and spatial and temporal distribution of major mortality factors must be understood to formulate the most effective management approaches.
Mortality linked to power lines has an influence on raptor populations, particularly in the case of Bonelli's eagle (Hernández-Matías et al. 2015), but it is not the only anthropogenic cause of mortality. This study of the causes of mortality with GPS transmitters has allowed us to detect other less spatially predictable causes such as direct persecution, including shooting or poisoning, and other causes such as intra- and interspecific predation, which are rarely reported in the literature. Moreover, it also explains how these causes are distributed over time and across space and allows for solutions to mitigate them.
An increase in the proportion of subadults that become territorial holders is an early warning signal of population decline in populations that are not colonizing new areas (Ferrer et al. 2003). Long-lived birds improve their reproductive success with age because of increased foraging skill and efficiency (Curio 1983). In our studies about breeding performance and laying date, we have already detected an increase in the amount of subadult Bonelli's eagles defending breeding territories and we have described how their presence is related to delayed laying date (López-Peinado and López-López 2024) and lower breeding performance (López-Peinado and López-López 2023). The high mortality rate detected in this study is directly related to the decrease in breeding success in the area, and both can affect the probabilities of population persistence.
The adult mortality values detected in this study are unnaturally high in a healthy population of any long-lived species and may lead to population extirpation in the next 50 years. Adult survival in large long-lived species is expected to be high (Sæther 1989) and for the Bonelli's eagle adult mortality has a larger effect on population growth rate than immature mortality (Real and Mañosa 1997, López-López et al. 2012). The probability of survival to 1 year was 71.6%, which is largely below the 87.13% previously reported in the area (Real and Mañosa 1997). Adult mortality values > 10% may lead to population decline in the short term (Hernández-Matías et al. 2011).
Causes of death
Obtaining an adequate estimation of the causes of mortality of mobile species is a challenge in most cases, even though these data are important to make management decisions (Cristescu et al. 2022). Some of the sources of mortality are spatially predictable, but most of them are neither temporally nor spatially predictable. The use of GPS technologies to track individuals is a tool that allows us to analyze the causes of mortality in a population with much less bias towards predictable causes (Klaassen et al. 2013). Previously detected mortality estimations (Real et al. 2001) included most of the causes reported in our study, although prevalence might be biased towards the more predictable causes (e.g., electrocution, collision with power lines). Our results indicate mortality has been previously underestimated and the undetected dead individuals could be behind the large-scale population decline that the species is suffering in eastern Spain.
As previously reported in other raptors (De Pascalis et al. 2020), unnatural mortality is notoriously more prevalent in our study population than natural mortality, although unreported natural mortality due to intra- and interspecific aggression should not be neglected in future estimations. Within anthropogenic mortality, most of the cases recorded for the Bonelli's eagle in Spain correspond to mortality linked to power lines (Perez-García et al. 2011, Hernández-Matías et al. 2015), especially through electrocutions (Real et al. 2001) but also due to collisions with power line wires.
Direct persecution by shooting and intentional poisoning is usually among the main causes of mortality in large raptors (Brochet et al. 2019) including Bonelli's eagle (Arroyo et al. 1995, Real et al. 2001, Hernández-Matías et al. 2015). The overall prevalence in the study population was greater than previously reported in our study area. Most of the cases were due to poisonings related to the elimination of raptors carried out by pigeon fanciers through the use of bait-pigeons with carbofurans smeared on their plumage. Three deaths were due to shooting. These occurred on days that hunting with firearms was not allowed (out of the hunting season) and there is no possibility of confusion of the species with others within the list of hunted species (Ley 13/2004, de 27 de diciembre, de caza de la Comunidad Valenciana). This, in contrast to previous studies (Martínez-Abraín et al. 2009), denotes that intentional persecution on Bonelli's eagles and raptors in general is far from being eradicated in eastern Spain.
Reduced availability of sources of natural water during drought accentuates the need for birds to use artificial water sources, some of which entrap the birds (Anderson et al. 1999). As availability of water sources are expected to decline with climate change (Tramblay et al. 2020), it would be expected that the incidence of this mortality cause may increase. Moreover, increased use of fences in rural landscapes may create more widespread collision hazards for Bonelli's eagles. Renewable energy infrastructure, especially wind turbines, can pose risks of mortality among some species of large raptors (Marques et al. 2014, Schuster et al. 2015, Dwyer et al. 2018), but its associated mortality has not been reported as high for Bonelli's eagle in Europe (Martínez et al. 2010, Hernández-Matías et al. 2015).
Temporal variation
Mortality can take place throughout the year, although March has the highest accumulated mortality. In March Bonelli's eagles are usually incubating (Arroyo et al. 1995, López-López et al. 2007a) and their vulnerability increases. The demand for food in large quantities increases their need for hunting and favors attacks on prey such as urban pigeons and other easy prey. This increases the number of interactions with pigeons cared and trained by pigeon fanciers and so increases the prevalence of direct persecution (López-López et al. 2009). In addition, mortality linked to predation by other large raptors is also more prevalent in March and April. Intraspecific competition is more intense at this time, either by floating individuals trying to acquire a territory or by competition for the use of resources between neighboring territories (Bosch et al. 2010, Morollón et al. 2022a). In addition, other large species of raptors coexist in the area and may prey on the Bonelli's eagle or eliminate it as a competitor, such as the golden eagle (A. chrysaetos) or the eagle owl (Bubo bubo; Bernis 1974, Martínez et al. 2008).
Spatial variation
The mortality rate of Bonelli's eagle was higher outside protected areas, as noted for some other species of raptors in the Mediterranean area (López-López et al. 2007b, Perez-Garcia et al. 2011). In most cases, the protection of areas implies management to reduce risk of mortality, such as minimizing electrocutions and collisions at power lines and greater vigilance to reduce direct persecution. Likewise, agricultural techniques are more restricted because of European Union agro-environmental regulations, and work has already been done to prevent drowning in artificial sources by installing exit ramps that help animals easily leave the water. As discussed in López-Peinado et al. (2023), habitat management inside of protected areas could be a straightforward conservation action to reduce the risks eagles are facing in their territories, but implementing actions outside the protected areas is still needed.
Prevalence of certain natural and non-natural causes of mortality differed between areas that were near versus far from the Mediterranean coast. Anthropogenic mortality was more prevalent near the coast, coinciding with higher human densities and development. Bonelli's eagles favorably select warm spaces, with a temperate annual climate, and areas of low elevation, particularly coastal areas, which coincides to a large extent with human preferences. Bonelli's eagles show a high tolerance, but no preference, for human presence (Gil-Sánchez 1996, Muñoz et al. 2005, Carrascal and Seoane 2009), but humans are a disturbance source that changes behavior of this species (Perona et al. 2019). Territories with a higher proportion of anthropogenic landscapes were abandoned in the study area (López-Peinado et al. 2024). Therefore, use of anthropogenic areas could be the result of the convergence in habitat selection by Bonelli's eagles and humans (Moleón et al. 2024).
CONSERVATION IMPLICATIONS
Strengthening and enforcing legal protections throughout the breeding range could help to reduce the decline of Bonelli's eagles in Spain. The results of our study reflect the need to continue to retrofit power line poles that pose risk of electrocution, especially those sited in habitat attractive to eagles. Direct persecution continues to be a major threat for the species, so it is necessary to increase vigilance on this type of illegal activity. The results of our study show a clear pattern in the incidence of poisoning and shooting and may serve to optimize the use of resources by increasing surveillance during critical periods (March seems to be the most relevant month for these activities). Collisions and drowning are already a cause of death for this and other species and we cannot rule out that their effect will increase in the coming years, so it would be necessary to continue correcting these elements through reducing the amount of fences, making them more visible, and building elements that allow the animals trapped in water ponds to get out of them to enhance survival. The combination of all these measures will help improve the conservation status of the Bonelli's eagle and other raptors in the Mediterranean basin.
ACKNOWLEDGMENTS
We thank C. García, F. García, A. Martínez-Perona, I. Estellés-Domingo, O. Egea-Casas, J. Martínez, and J. M. Lozano for their help in fieldwork. We also thank the forest rangers and the staff of Valencia and Castellón Wildlife Recovery Centers for their collaboration during our study. Special thanks to the regional government (Generalitat Valenciana) for support throughout the study. Red Eléctrica de España, Iberdrola Foundation, ACCIONA Eólica de Levante, LafargeHolcim and Generalitat Valenciana also provided financial support to track eagles. Since 2023 this study was funded by the Spanish Ministry of Science and Innovation (project TED2021-131653A-I00) with the support of NextGenerationEU funds. The corresponding author A. L-P. was supported by a Val I+D predoctoral grant (ACIF/2020/051), funded by the Generalitat Valenciana (Spain) and Fondo Social Europeo (FSE). This paper is part of Andrés López Peinado's doctoral thesis at the University of Valencia.
CONFLICT OF INTEREST STATEMENT
The authors declare no conflict of interest.
ETHICS STATEMENT
Handling activities were authorized and conducted under permissions issued by regional authorities (Generalitat Valenciana and Junta de Comunidades de Castilla—La Mancha) and all efforts were made to minimize handling time to avoid any suffering to eagles.
Open Research
DATA AVAILABILITY STATEMENT
Data used in this study are publicly available under request in the online data repository Movebank (www.movebank.org), projects ID = 58923588 and 193515984.
REFERENCES
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Associate Editor: James Sheppard.
