Foraging Patterns of Non-Territorial Eastern Imperial Eagle (<i>Aquila heliaca</i>): A Case of Successful Adaptation

The Optimal Foraging Theory predicts that, to maximize fitness, animals adapt their foraging strategy that provides the most benefit for the lowest cost, maximizing the net energy gained. While the diet of many breeding raptor populations is well known, studies on the foraging patterns of non-territorial birds of prey (floaters) are scarce. In this study, we examined the foraging pattern of non-territorial Eastern Imperial Eagle, scrutinizing different aspects of its feeding ecology and behavior. We built a simple model of the optimal foraging strategy of floater eagles including the success of foraging as a currency as well as environmental factors such as seasons, type of prey, habitat, foraging techniques, and eagle age as a limitation affecting the foraging efficiency of birds. We found that floaters focused their diet exclusively on European Souslik, accounting for almost half (44.2%) of the eagle’s prey. Diet differences between floaters and breeders were due to higher Souslik and carrion consumption and lower Hedgehog predation by floater eagles. The diet diversity of breeding eagles (H = 3.297) was much higher than that of floaters (H = 1.748). Our model suggested that the foraging mode, habitat type, and season best explained the feeding success of non-territorial eagles (ΔAIC = 0.00, w = 0.42). Of all explanatory factors, “Kleptoparasitism” (β2 = −4.35), “Rodents” (β2 = −4.52), “Pasture” (β2 = 2.96), “Wheat” (β2 = 4.41), “In the air” (β2 = 4.16), and “Other habitats” (β2 = 4.17) had a pronounced effect. The factors “Spring–summer season” (β2 = −0.67) and “European Souslik” (β2 = −2.76) had a marginal effect in our models. Generally, the mean success rate of attack modes used by non-territorial eagles was 0.54 ± 0.50. Floaters successfully obtained food through: kleptoparasitism (43.10%), carrion feeding (24.14%), and high soar with vertical stoop (14.66%). Several important issues for the conservation of non-territorial Eastern Imperial Eagles arose from our research. The strong relation of floaters with the European Souslik calls for specific conservation measures aimed at the conservation of this type of prey and the restoration and appropriate management of its grassland habitats. The importance of the scavenging behavior of juvenile birds requires increased control of the use of poison baits and subsequent prosecution by state institutions. Protecting the most important temporary areas, improving institutional control against the use of poison baits, and intensifying awareness-raising campaigns among pigeon-fanciers and hunters are also of crucial importance for effective species conservation

Conservation and Ecology of Raptors: Introduction to the Special Issue

Raptors are a diverse avian guild distributed worldwide and adapted to different environments [...

Foraging Patterns of Non-Territorial Eastern Imperial Eagle (Aquila heliaca): A Case of Successful Adaptation

The Optimal Foraging Theory predicts that, to maximize fitness, animals adapt their foraging strategy that provides the most benefit for the lowest cost, maximizing the net energy gained. While the diet of many breeding raptor populations is well known, studies on the foraging patterns of non-territorial birds of prey (floaters) are scarce. In this study, we examined the foraging pattern of non-territorial Eastern Imperial Eagle, scrutinizing different aspects of its feeding ecology and behavior. We built a simple model of the optimal foraging strategy of floater eagles including the success of foraging as a currency as well as environmental factors such as seasons, type of prey, habitat, foraging techniques, and eagle age as a limitation affecting the foraging efficiency of birds. We found that floaters focused their diet exclusively on European Souslik, accounting for almost half (44.2%) of the eagle&rsquo;s prey. Diet differences between floaters and breeders were due to higher Souslik and carrion consumption and lower Hedgehog predation by floater eagles. The diet diversity of breeding eagles (H = 3.297) was much higher than that of floaters (H = 1.748). Our model suggested that the foraging mode, habitat type, and season best explained the feeding success of non-territorial eagles (&Delta;AIC = 0.00, w = 0.42). Of all explanatory factors, &ldquo;Kleptoparasitism&rdquo; (&beta;2 = &minus;4.35), &ldquo;Rodents&rdquo; (&beta;2 = &minus;4.52), &ldquo;Pasture&rdquo; (&beta;2 = 2.96), &ldquo;Wheat&rdquo; (&beta;2 = 4.41), &ldquo;In the air&rdquo; (&beta;2 = 4.16), and &ldquo;Other habitats&rdquo; (&beta;2 = 4.17) had a pronounced effect. The factors &ldquo;Spring&ndash;summer season&rdquo; (&beta;2 = &minus;0.67) and &ldquo;European Souslik&rdquo; (&beta;2 = &minus;2.76) had a marginal effect in our models. Generally, the mean success rate of attack modes used by non-territorial eagles was 0.54 &plusmn; 0.50. Floaters successfully obtained food through: kleptoparasitism (43.10%), carrion feeding (24.14%), and high soar with vertical stoop (14.66%). Several important issues for the conservation of non-territorial Eastern Imperial Eagles arose from our research. The strong relation of floaters with the European Souslik calls for specific conservation measures aimed at the conservation of this type of prey and the restoration and appropriate management of its grassland habitats. The importance of the scavenging behavior of juvenile birds requires increased control of the use of poison baits and subsequent prosecution by state institutions. Protecting the most important temporary areas, improving institutional control against the use of poison baits, and intensifying awareness-raising campaigns among pigeon-fanciers and hunters are also of crucial importance for effective species conservation

Does Temporal and Spatial Diet Alteration Lead to Successful Adaptation of the Eastern Imperial Eagle, a Top Predator?

Predator&ndash;prey interactions may be linked to different temporal or spatial patterns, including dynamics in prey populations. Therefore, understanding the adaptive capacity and how top predators respond to shifts in prey abundance and availability is crucial for their conservation. In this study, we investigated the diet pattern of the endangered Eastern Imperial Eagle facing long-term and large-scale changes. We studied the abundance variation of its profitable prey, sousliks, and how it reflected on eagle population trajectories in a regional and temporal context. We found a significant diet alteration expressed in large decrease of brown hare (&beta;2 = &minus;0.83), poultry (&beta;2 = &minus;0.81), gulls (&beta;2 = &minus;0.71), and water birds (&beta;2 = &minus;0.57), and an obvious increase of northern white-breasted hedgehog (&beta;2 = 0.61) and doves (&beta;2 = 0.60). Raptors and owls raised their participation (&beta;2 = 0.44), but white stork and different reptiles supplied more biomass. Abundance of European souslik decreased through the studied periods (adjusted R2 = 0.25, p &lt; 0.001) which accounted for the lower proportion of this prey in the eagle&rsquo;s diet. Nevertheless, the eagle population successfully adapted and significantly increased (&beta;2 = 0.97) in most of the distribution area. The trophic strategy used by this top predator related to opportunistic foraging represents an ecological advantage that allows the species to adapt to different habitats and guarantees its future. The observed prolonged diet alteration could result in a significant negative attitude among different groups such as hunters, pigeon fanciers, and poultry keepers towards eagles. Therefore, enhanced communication with key stakeholders is needed. Conservation efforts should be focused also on the preservation of the species&rsquo; main foraging habitats and the restoration of damaged ones so as to maintain the good conditions of both primary food source and subsequent prey

Does Temporal and Spatial Diet Alteration Lead to Successful Adaptation of the Eastern Imperial Eagle, a Top Predator?

Predator–prey interactions may be linked to different temporal or spatial patterns, including dynamics in prey populations. Therefore, understanding the adaptive capacity and how top predators respond to shifts in prey abundance and availability is crucial for their conservation. In this study, we investigated the diet pattern of the endangered Eastern Imperial Eagle facing long-term and large-scale changes. We studied the abundance variation of its profitable prey, sousliks, and how it reflected on eagle population trajectories in a regional and temporal context. We found a significant diet alteration expressed in large decrease of brown hare (β2 = −0.83), poultry (β2 = −0.81), gulls (β2 = −0.71), and water birds (β2 = −0.57), and an obvious increase of northern white-breasted hedgehog (β2 = 0.61) and doves (β2 = 0.60). Raptors and owls raised their participation (β2 = 0.44), but white stork and different reptiles supplied more biomass. Abundance of European souslik decreased through the studied periods (adjusted R2 = 0.25, p 2 = 0.97) in most of the distribution area. The trophic strategy used by this top predator related to opportunistic foraging represents an ecological advantage that allows the species to adapt to different habitats and guarantees its future. The observed prolonged diet alteration could result in a significant negative attitude among different groups such as hunters, pigeon fanciers, and poultry keepers towards eagles. Therefore, enhanced communication with key stakeholders is needed. Conservation efforts should be focused also on the preservation of the species’ main foraging habitats and the restoration of damaged ones so as to maintain the good conditions of both primary food source and subsequent prey

Bird community patterns in sub– Mediterranean pastures: the effects of shrub cover and grazing intensity. Animal Biodiversity and Conservation

Abstract Bird community patterns in sub-Mediterranean pastures: the effects of shrub cover and grazing intensity.-Shrubs are widely considered a threat to grassland biodiversity. We investigated the effects of shrub cover and grazing intensity on bird communities in sub-Mediterranean pastures in Bulgaria. The point-count method was used on 80 plots in open (&lt; 10% shrub cover) and shrubby (approx. 20% cover) pastures under either intensive or extensive management (grazing intensity) from 2008 to 2009. We recorded a total of 1,956 observations of birds from 53 species. Main environmental gradients accounting for the bird community pattern were related to vegetation succession and land productivity. Bird species richness was higher in shrubby pastures than in open sites, while no effect was found in respect to total bird abundance. Bird species diversity (i.e. H&apos; index) was highest in extensive shrubby pastures. Shrubland specialists were positively affected by shrub cover and extensive management of pastures while grassland and woodland specialists showed no significant response to these factors. We conclude that a small proportion of shrubs within pastures may be beneficial for farmland birds and sustainable management of pastures could be achieved by greater flexibility of national agri-environmental schemes. Key words: Agri-environmental scheme, Farmland birds, Grassland management, Semi-natural habitats, Shrubby vegetation. Resumen Patrones de las comunidades de aves en los pastos submediterráneos: el efecto de la cubierta arbustiva y la intensidad de pastoreo.-Se suele considerar a los arbustos como una amenaza a la biodiversidad de los pastos. Investigamos los efectos de la cubierta arbustiva y la intensidad del pastoreo sobre las comunidades de aves en los pastos submediterráneos de Bulgaria. Se utilizó el método de estaciones de escucha en 80 puntos de registro en pastos abiertos (cubierta arbustiva &lt; 10%) y arbustivos (aproximadamente un 20% de la superficie cubierta), con una gestión de pastoreo tanto intensiva como extensiva desde 2008 a 2009. Registramos un total de 1.956 observaciones de aves pertenecientes a 53 especies distintas. Los gradientes ambientales principales responsables de los patrones de las comunidades de aves se relacionaron con la sucesión de la vegetación y la productividad de la tierra. La riqueza de especies de aves era mayor en los pastos arbustivos que en los lugares abiertos, aunque no se observó efecto alguno con respecto a la abundancia total de aves. La mayor diversidad de especies de aves (índice H&apos;) se daba en los pastos arbustivos con gestión extensiva. Los especialistas en zonas arbustivas se veían afectados positivamente por la cubierta arbustiva y la gestión extensiva de los pastos, mientras que los especialistas de praderas y bosques no presentaron ninguna respuesta positiva a dichos factores. Nuestra conclusión es que una pequeña proporción de arbustos dentro de los pastos puede ser beneficiosa para las aves de tierras de labrantío, y la gestión sostenible de los pastos podría alcanzarse mediante una mayor flexibilidad de los esquemas agroambientales nacionales

Observations on the behavior of the saker falcon (Falco cherrug) breeding in Bulgaria

Saker falcon populations suffered severe declines, especially in the second half of the 20th century. During the period between 2004 and 2018, the species became extinct in Bulgaria as a breeding species. After that, a reintroduction program was implemented with birds originating from central Europe. We studied the main behavioral characteristics of both wild sakers from the local population of the species in SE-Bulgaria and these of the reintroduced birds which started breeding in the same region in a wild in 2018. We collected numerous observations on the territorial, hunting, and breeding (parental) behavior of that species. Territorial attacks against 16 bird species were recorded with prevailing numbers against kestrel (Falco tinnunculus) and imperial eagle (Aquila heliaca). The main hunting strategies of the species included attacks against sousliks (Spermophilus citellus) in their numerous colonies in the study area. Various species of birds were also captured and brought in the nest. Adults were feeding the nestlings in 31.5–55.3 min intervals depending on their age. In the morning hours (7 am – 12 pm) the duration of the feeding of the nestlings is lower – 11.35±3,5 min on average, compared to the afternoon (12 pm – 5 pm) – 18.81±6,81 min. After the disappearance of a female in 2021, the male alone fed and cared for three nestlings during a period of 19 days. The male stopped feeding the nestlings after finding another female and consequently all the nestlings were found dead

Breeding performance and population trend of the Egyptian Vulture Neophron percnopterus in Bulgaria: conservation implications

The Egyptian Vulture (Neophron percnopterus) has been classified as ‘Endangered’ due to rapid population declines across its range. Thus, exhaustive studies on its demography may serve as an important stepping stones for successful conservation programs. Breeding performance is one of the main components of the demography of a raptor population. Evaluating reproductive rates is easier than other demographic parameters, while remaining a very useful metric to identify factors driving raptor population trends. Here we present the breeding performance of the species’ population in Bulgaria as a result of a long-term monitoring (2005–2016). The studied population shows high breeding performance, based on a breeding success (1.11 ± 0.13 fledglings / laying pairs), productivity (0.88 ± 0.1 fledglings / occupied territories) and fledgling success (1.2 ± 0.1 fledglings / successful pairs), all among the highest recorded in Europe. Pairs breeding in territories with high occupancy rate produced 88% of the fledglings