Touchdown Rate and Success in Vole Hunting by Wintering Hen Harriers (Circus cyaneus): Roles of Intrinsic and Extrinsic Factors

Raptors wintering in temperate regions face strong energetic constraints due to low temperatures and limited prey availability. Understanding how intrinsic traits and environmental conditions shape hunting performance helps to clarify the mechanisms underlying winter foraging efficiency. We studied wintering Hen Harriers (Circus cyaneus) in Austria over five consecutive winters (2020/21–2024/25) to quantify touchdown attempt rate and outcome in relation to sex, age, territorial status, and weather. Using generalized linear mixed models, we analyzed 1829 recorded touchdowns with individual identity as a random effect. Territorial females showed slightly higher attempt rates than males, whereas non-territorial females exhibited a tendency toward lower touchdown success. Adult males achieved the highest per-attempt efficiency, but age alone had no significant effect. Touchdown outcomes improved under cloud cover and declined with wind speed, while temperature showed no influence. Attempt rate was unaffected by any environmental variable. These results demonstrate that both intrinsic and extrinsic factors jointly determine winter foraging performance: males, with their smaller body size and agility, can persist even in vole-poor habitats by compensating through efficient flight and prey capture; territorial females benefit from stable access to vole-rich patches; and non-territorial females remain constrained by competition and limited access to prey. The findings highlight the need to maintain open farmland and vole-rich habitat to support diverse overwintering strategies.