Availability of optimal‐sized prey affects global distribution patterns of the golden eagle Aquila chrysaetos

Abstract

Climate and landscape change are expected to significantly affect trophic interactions, which will especially harm top predators such as the golden eagle Aquila chrysaetos. Availability of optimal prey is recognized to influence reproductive success of raptors on a regional scale. For the golden eagle, medium‐sized prey species between 0.5 and 5 kg are widely considered to be optimal prey during the breeding season, whereas smaller and larger species are deemed as energetically sub‐optimal. However, knowledge about the effects of optimal prey availability is still scarce on larger scales. To decrease this apparent knowledge gap, we combined biogeographical information on range margins with information about the foraging behaviour and reproductive success of golden eagles from 67 studies spanning the Northern Hemisphere. We hypothesized that availability of optimal prey will affect foraging behaviour and breeding success and, thus, distribution patterns of the golden eagle not only on a local but also on a continental scale. We correlated the diet breadth quantifying foraging generalism, breeding success and proportions of small (< 0.5 kg), medium (0.5–5 kg) and large‐sized (> 5 kg) prey species within the diet with the minimum distance of the examined eagles to the actual species distribution boundary. Closer to the range edge, we observed decreased proportions of medium‐sized prey species and decreasing breeding success of golden eagles. Diet breadth as well as proportions of small and large‐sized prey species increased, however, towards the range edge. Thus, availability of optimal‐sized prey species seems to be a crucial driver of foraging behaviour, breeding success and distribution of golden eagles on a continental scale. However, underlying effects of landscape characteristics and human influence on optimal prey availability has to be investigated in further large‐scale studies to fully understand the major threats facing the golden eagle and possibly other large terrestrial birds of prey.

Size dependency in colour patterns of Western Palearctic carabids

“…Such models allow for the identification of thresholds in ecological relationships (cf. Toms and Lesperance , Gentile and Argano , Schweiger et al ). The identification of thresholds is of particular importance for relationships dealing with thermoregulatory habits linked to the body size of ectotherms.…”

Spatial and Temporal Patterns in Golden Eagle Diets in the Western United States, with Implications for Conservation Planning

“…The abundance and availability of prey in the preferred size range may influence Golden Eagle distribution at continentwide scales (Schweiger et al 2015). The exception was the high percentage of smaller-bodied ground squirrels in the Northern Basin and Range (B. Woodbridge unpubl.…”

Conservation implications of harpy eagle Harpia harpyja predation patterns

“…Combining these theories can lead to optimality-based re search which can efficiently monitor populations of threatened species. Foraging theory can explain underlying needs and preferences, as well as fundamental community organization (Agü -era et al 2015, Schweiger et al 2015. Over much of its range, the harpy eagle forages principally on prey species that have exceptional morphological and behavioral traits to avoid detection.…”

“…Predation patterns can be affected by a wide range of ecological constraints that vary across the geographic range of the predator species. Thus, local food habit descriptions may well have little practical utility in a range-wide conservation framework (Hayward & Kerley 2005, Schweiger et al 2015. Other than local descriptions of prey-base composition, such studies may offer little to improve the effective management of this type of species.…”