Factors Associated with Space Use and Reproductive Success of American Kestrels in Northern Virginia, USA

Abstract

Understanding how breeding-season space use varies across individuals and landscapes can provides insight into the resource requirements of species. My thesis evaluated the space use of American kestrels (Falco sparverius), a species of conservation concern, and tested whether their movement behavior was associated with sex-specific parental roles, local resource availability, and central-place foraging theory as a framework for linking movement to reproductive success. From 2021 to 2024, I used GPS loggers to track 69 kestrels (male = 27, female = 42) in northern Virginia and monitored nesting attempts (n = 48) for reproductive outcomes. Mean range size across stages during the breeding season (incubation, nestling, fledgling, post-breeding, and shifted post-breeding) was 0.51 km² (95% CI: 0.42 – 0.61, range 0.01 km²–4.27 km²), and median distance traveled from nest box was on average 325.26 m (SD: ± 495.36, range 5.82–3628.11 m). A post-breeding range shift occurred in 16% of nesting attempts. Model comparisons using AICc indicated space use varied by sex and stage during the parental care period (nestling and fledgling stages), with males exhibiting consistently larger ranges and distances traveled than females. Female space use increased during the fledgling stage, reflecting shared provisioning responsibilities. By post-breeding stage, both sexes had comparable space use, likely reflecting release from parental duties. Higher availability of meadow and hay within 600 m of the nest box were associated with smaller range sizes and shorter distances traveled from the nest box, although meadow availability increased distances traveled during the fledgling stage. In contrast, increased forest availability was associated with larger median distances traveled from nest box and an increased probability of post-breeding range shifts. Median distance traveled from nest box was not associated with number of fledglings or the proportion of nestlings fledged. However, earlier clutch initiation dates and increased use of pasture were positively associated with fledging success. These findings provide partial support for central-place foraging theory, suggesting that kestrels offset energetic costs of increased movement from the nest box through selective habitat use. This is the first study to quantify breeding-season space use for both male and female kestrels using high-resolution GPS tracking. The results highlight how specific cover types—particularly meadow, hay, and forest—influence kestrel space use, and kestrels who foraged more in pasture had greater reproductive success. Land cover within a 600 m radius of kestrel nest boxes had the largest effect on range size and median distance traveled. Additionally, the relatively small range sizes observed in this study suggests that land cover in the piedmont region of northern Virginia may represent high-quality habitat capable of supporting higher kestrel densities. My results provide land managers and policy makers with information useful for decision making regarding habitat management and informing nest box placement for kestrels.