Movement patterns of an avian generalist predator indicate functional heterogeneity in agricultural landscape

Abstract

Biodiversity is closely related to landscape heterogeneity, but both are difficult to evaluate directly. Apex predators, such as raptors, are potential surrogate indicators of diversity, but previous studies using a correlative approach have been heavily criticised. We evaluated whether space use by a generalist avian predator, the lesser spotted eagle Clanga pomarina, is an effective indicator of functional landscape heterogeneity and evaluate mechanisms driving this relationship. We used GPS-tracking of eagles over eight breeding seasons along with precise field mapping data for broad and detailed land-use types from Estonia, Eastern Europe. We analysed the effects of various landscape metrics and composition on movement patterns of eagles. Activity centres of eagles were associated with configurational heterogeneity, as evidenced by their foraging on the edges of small complex patches more often than expected at random. The eagles also avoided roads (disturbance) and preferred forest edges (ecotones with abundant prey and perch sites). The importance of compositional heterogeneity was revealed by preferences for specific land-use types (e.g. spring-sown but not autumn-sown wheat); preferred crops changed over time. The model including only general land-use classes was outperformed by the model based on a detailed classification. Movement ecology provides an opportunity to biomonitor the heterogeneity of landscapes and adds a functional perspective to earlier raptor-biodiversity correlation studies. This suggests that in addition to GPS-tracking, large quantities of opportunistic observations by citizen scientists can be used to evaluate biodiversity across landscapes.