Home-Range Size and Space Use of Territorial Bonelli's Eagles (Aquila fasciata) Tracked by High-Resolution GPS/GSM Telemetry

High-resolution GPS/GSM dataloggers provide spatial information of the highest quality, which outperform previous tracking methods, such as Argos telemetry or conventional VHF ground-tracking. As a result, this has improved our knowledge of home-range behavior and spatial ecology of many species, including large raptors. In this paper, we use high-resolution GPS/GSM dataloggers to assess the home-range size and the role of sex, season (breeding or non-breeding season), and breeding status (reproductive or non-reproductive individuals) on the space use of Bonelli's eagle (Aquila fasciata). To this end, 51 territorial individuals (25 females and 26 males) were equipped with GPS/GSM transmitters and were tracked over 7 years (2015-2021) in eastern Spain. Overall, we recorded 4,791,080 fixes that were analyzed through kernel density methods (50%, 75%, and 95% fixed kernels). The average individual home-range size according to the 95%, 75%, and 50% kernels was 54.84 +/- 20.78 km(2), 24.30 +/- 10.18 km(2), and 11.17 +/- 4.90 km(2), respectively. Overall, the home-range size of individuals occupying the same territory was similar, mainly due to the cooperative hunting behavior exhibited by the species. We did not find interannual differences in the home-range size (95% fixed kernel) of the majority of individuals, showing a strong territorial fidelity of the breeding pairs. In general, females' home-range size was slightly smaller than males' size due to the decrease in activity in the breeding season as a result of laying, incubation, and chick attendance at nests. No seasonal variation in the 95% kernel was found, but it was found in the 75% and 50% kernels. In regard to the breeding status, higher home-range size was recorded in the non-reproductive individuals. Moreover, we found a low neighbor overlap among the territories (4.18% +/- 3.06%), which evidences a high level of intraspecific competition in the Bonelli's eagle. Finally, this study highlights the advantages of the use of accurate telemetry information to improve our understanding of the spatial ecology of the endangered Bonelli's eagle, which ultimately will serve to better inform management actions for its conservation.

Automated summary

High-resolution GPS/GSM dataloggers provide high-quality spatial information that improves our understanding of home-range behavior and spatial ecology. This paper examines the home-range size and the influence of sex, season, and breeding status on the space use of Bonelli's eagle using high-resolution GPS/GSM dataloggers. The study finds that home-range size is similar among individuals occupying the same territory, primarily due to cooperative hunting behavior. Females have slightly smaller home ranges, likely due to reduced activity during the breeding season. There is low neighbor overlap, indicating high intraspecific competition among Bonelli's eagles.