Weak niche partitioning between closely related sympatric Greater (Clanga clanga) and Lesser Spotted Eagles (C. pomarina)

Abstract

Species coexist only when occupying different ecological niches. We evaluated habitat and trophic niches in two recently diverged hybridizing avian apex predators, the declining Greater Spotted Eagle Clanga clanga (mainly found in contracting wetlands) and the more numerous Lesser Spotted Eagle Clanga pomarina (inhabiting mosaic farmlands). We tracked 24 Spotted Eagles, including interspecific hybrids, by GPS to estimate the home‐range size, land use composition and landscape structure in sympatric populations. In addition to information for landscape utilization, data for diet composition were evaluated. Home‐ranges of the two species were similar in size and open foraging habitats consisted mostly of agricultural landscape. However, landscape utilization of the Greater Spotted Eagle was largely driven by the composition of land‐use types, whereas the Lesser Spotted Eagle was mostly influenced by structural components of the landscape. Farmland‐dwelling voles accounted for the bulk of the diet in both species; however, subdominant prey classes differed. Hybrids exhibited intermediate or mixed features of home‐ranges and diets. Our results provide evidence for reduced niche partitioning and potential competition between the two Spotted Eagles, which may have been reinforced by anthropogenic habitat alteration. A closer examination of movement patterns revealed previously overlooked differences between closely related species with respect to landscape utilization strategies.