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.

Movement of avian predators points to biodiversity hotspots in agricultural landscape

“…Of course, even among generalists, some individuals may exhibit specialization in particular types of prey [ 59 – 61 ], and certain prey species may be more preferred due to higher rewards. In our study area, small mammals constituted a significant portion of the diet for the common buzzard [ 62 ], lesser spotted eagle [ 63 – 65 ] and western marsh harrier (Ü.V., unpublished data). This aspect did influence our results to some extent since the richness and abundance of small mammals emerged as significant predictors of hotspots in our study.…”