Nest spacing and diet selection in a unique multi-species community of Eagles in Central Asia [Espacement des nids et sélection alimentaire dans une communauté multi-spécifique des aigles d’Asie centrale].

Résumé

We studied nest spacing and dietary selection in a unique community of Imperial (Aquila heliaca), Golden (A. chrysaetos) and Steppe (A. nipalensis) Eagles and White-tailed Sea Eagles (Haliaeetus albicila) at the Naurzum Zapovednik (Nature Reserve) in north-central Kazakhstan. Nearest neighbor distance to any active nest of the three tree-nesting species was 2730 ± SD of 1236 m (N = 37). Nearest conspecific neighbor distance was 3462 ± 1185 m (N =29) for Imperial Eagles and 5396 ± 4862 m (N = 6) for White-tailed Sea Eagles. The three forested areas of the Zapovednik have different landscape configurations and nest site characteristics. Consequently, nest spacing patterns were different in each area. Dietary (niche) overlap among eagle species was significantly less than would be expected based on random allocation of available prey (P Spermophilus fulvus and S. major], marmots [Marmota bobac], large corvids [Corvus corone and C. frugilegus], and small mammals [Cricetidae and Muridae]), only the small mammals were taken in different amounts by the four eagle species (P Anas spp., Podiceps spp., and Fulica atra) and owls (Asio spp.) were represented differently in eagle diets (P < 0.05). Analysis of diet suggests that a high degree of niche partitioning may permit the exceptionally high density of breeding eagles to coexist in such unusually close proximity. However, when analysis of diet is integrated with spatial patterns, it appears that nest location (and therefore local prey availability) may be as important a determinant of diet as is interspecific variation. We are directing future work in this system at elucidating and refining understanding of these trends through continued observation of nest spacing, population turnover rates, dietary analysis, and defining prey availability throughout the region.