Interannual home range variation, territoriality and overlap in breeding Bonelli’s Eagles (Aquila fasciata) tracked by GPS satellite telemetry

Abstract

Animal movement patterns and use of space depend upon environmental resources (i.e., food availability), and on conspecific and interspecific interactions. We studied the home range of seven territorial Bonelli’s Eagles (Aquila fasciata) tracked by GPS satellite telemetry over a period of 4–5 years to determine home range characteristics and annual and individual variations. Bonelli’s Eagles hold an annual home range of Minimum Convex Polygon (MCP) = 205.6 km2 (range 44.7–704.8 km2 ) and Kernel 95 % = 44.4 km2 (range 31.8–91.9 km2 ). Eagles showed slight temporal variation in home range sizes, but a wide variation in use of space. Only 27.3 % of the accumulated home range was used during all seasons, while 30.3 % was used only during a single season. Areas around the nest, main hunting areas and roosting sites were utilised regularly every year in both breeding and non-breeding seasons. Accumulated home ranges were stabilised in year 3 of monitoring. Individuals displayed strong territoriality, even in non-breeding seasons, although eagles also made long trips ([15 km) well beyond their territorial boundaries, as assessed for the first time by GPS satellite telemetry. The overlap was slight for two adjacent pairs. In addition, we noticed a strong relationship between topographical landmarks and home range segregation. This study reinforces the idea that combining information on season patterns, conspecific distribution and topography can help define both the shape and size of home ranges more realistically.