Long-term changes in the breeding period diet of Bonelli

Abstract

Context Dietary analyses are essential to achieve a better understanding of animal ecology. In the case of endangered species, assessing dietary requirements is crucial to improve their management and conservation. The Bonelli’s eagle (Aquila fasciata) has experienced a severe decline throughout its breeding range in Europe and, in Italy, fewer than 50 pairs remain, and only in Sicily. This species is subject to major threats, including changes in landscape composition and, consequently, prey availability, which is further aggravated by the occurrence of viral diseases in the case of rabbits. Aims To provide current data on the diet of the Bonelli’s eagle in Sicily during the breeding period and to examine dietary shifts with regard to previous studies conducted in the same study area. To discuss possible implications for conservation of the Italian population of this endangered species. Methods We used a combination of three methods, including pellet analysis, collection of prey remains, and imagery from camera-traps installed at nests, to examine the diet of 12 breeding pairs of Bonelli’s eagle from 2011 to 2017. We compared this information with data collected between 1993 and 1998 in the same study area. Key results In number, birds were the most frequently predated items (61.6%), followed by mammals (36.88%) and reptiles (1.52%). However, in terms of biomass, mammals were the main prey (65.71%), followed by birds (34.12%) and reptiles (0.17%). There was a decrease over the course of the current decade in the consumption of European wild rabbit (Oryctolagus cuniculus), which was compensated for with an increase in both dietary diversity and breadth in bird consumption, a trend not observed in the earlier study in the same region. Conclusions Here, we provide an updated assessment of diet composition of Bonelli’s eagle during the breeding period. Interestingly, we found significant differences within the study period (2011–2017) in terms of frequency of occurrence, percentage of biomass, dietary diversity and dietary breadth in a species at risk. Furthermore, we found significant differences between the two study periods in both frequency and percentage of biomass, with significant changes in the consumption of lagomorphs and birds. Implications Our results indicated that shifts in the diet are linked to changes in prey abundance, which may be contributing to population declines in the Bonelli’s eagle population in Sicily. Overall, measures aimed at increasing main dietary prey should be promoted to favour occupation of new territories and enhance vital demographic parameters (i.e. breeding success and survival rate) of Bonelli’s eagle across the species range. This would be particularly important for small isolated populations such as the Sicilian one.

Potential negative effects of the installation of video surveillance cameras in raptors’ nests

“…For example, the study of Bonelli's eagle diet, which was the main justification for the installation of cameras in Bonelli's eagle nests by the regional government, has been a topic deeply studied for decades (e.g. 12,[61][62][63][64][65][66][67][68][69][70][71][72] , among many others). Therefore, the timeliness and novelty of the intervention, if other goals are not considered, could also be questioned.…”

Similar post-fledging behavior observed in wild and reintroduced juvenile Bonelli’s Eagle in two Mediterranean islands

“…These circumstances led to the Bonelli's Eagle being considered by the IUCN as “nearly threatened” in Europe (BirdLife International 2022). Their diet consists mainly of rabbits, pigeons, and partridges, although they can feed on other birds, mammals, and lizards (López-López and Urios 2010, Di Vittorio et al 2019). Bonelli's Eagles usually breed between January and June nesting in cliffs and trees.…”