Impacts of Habitat Type on Individual Prairie Falcon (Falco Mexicanus) Movement and Foraging Behavior During the Breeding Season
Authors: Ravecca Eden Sunshine 
Published: July 2024

Animal movement is a fundamental characteristic of the ecology, fitness, and evolution of species. Movement behavior can differ significantly among individuals within a population and is driven by a multitude of factors, both intrinsic and extrinsic. How and why animals differ in the way they use habitat is central to species conservation, but relying solely on population-level estimates obscures individual variation and can result in ineffective management strategies. Understanding the mechanistic underpinnings of movement and individual variation among wide-ranging aerial predators is particularly challenging, but remains imperative for conservation, given the critical role of higher trophic levels in ecosystem functioning. I aimed to examine functional habitat use (i.e., why animals move in specific habitats), individual variability, and seasonal variation in movement of breeding Prairie Falcons within the Morley Nelson Snake River Birds of Prey National Conservation Area (NCA) in southwest Idaho. I deployed GPS-GSM telemetry units on adult Prairie Falcons to track their movement during the breeding seasons of 2021 and 2022. Using a two-state hidden Markov model, I quantified individual differences in how 17 Prairie Falcons moved through four structurally different habitat types (sagebrush, non-sagebrush shrub, annual herbaceous and perennial herbaceous) throughout the breeding season. The model categorized their movements while in flight into two behavioral states: (1) ‘canted’, relatively slow and tortuous movement, likely associated with foraging behaviors including prospecting, high-angle stoops, or high-maneuvering hunting; and (2) ‘strafing’, relatively fast and directional movement likely associated with commuting to foraging areas or high-speed, direct-pursuit hunting. We did not detect consistent effects of habitat type on Prairie Falcon movements. Instead, Prairie Falcons varied widely in their functional use across habitat types within the NCA, a dryland ecosystem comprised of sagebrush steppe with varying levels of degradation. Multiple individuals exhibited a decrease in the probability of transitioning from strafing to canted movement states when encountering higher a percentage of native sagebrush cover, while others exhibited an increase in that transition probability as invasive annuals increased. In a canted movement state, many individuals exhibited more directional movement as native sagebrush or native perennials increased. As the brood-rearing period progressed, Prairie Falcons increased the proportion of time spent in a strafing movement state, suggesting increased travel distances or foraging trips when food demand is the highest. The versatility among individual Prairie Falcons was evident across all four habitat types and suggests that these falcons can adapt their behavior, regardless of whether they are in native or nonnative habitats. This hints at the potential resilience of the species and their ability to deal with ongoing habitat degradation. Understanding functional habitat use can inform effective conservation strategies, while individual differences provide insights into the adaptive capacity of Prairie Falcon populations in a rapidly changing world.