Seasonal home range variation and spatial ecology of peregrine falcons (Falco peregrinus) in coastal Humboldt County, CA

Peregrine falcons (Falco peregrinus) are renowned for their migratory habits, with ‘peregrinus’ often translated as ‘wanderer’ or ‘pilgrim’. However, their migratory habits may differ by population and some peregrine may falcons forgo migration when climate and resources remain stable. To examine peregrine falcon home range and space use, I fitted GPS-satellite transmitters to nine breeding adults in coastal northern California, an area with a mild climate and abundant waterbird populations. I used kernel density estimates and time-local convex hulls to examine seasonal home ranges and within-home range habitat use. All nine peregrine falcons remained resident in their territories year-round, and home ranges continued to center around the location of the nesting structure (i.e. bridge or cliff face) even during winter. Home range sizes were larger in the breeding season than in winter, indicating that peregrines did not need to travel farther to find food during the winter and that local conditions were conducive to year-round occupancy. Intensity of space use within the home range was influenced by several environmental covariates, including distance to water, distance to nest site, elevation, prey density, terrain ruggedness and habitat type. Peregrine falcons preferred habitat types associated with nest sites, where they remained year-round, and with open areas such as mud flats, beaches, some agricultural lands, and inland standing water. Intensity of use decreased with distance from bodies of water, distance from nest sites, and terrain ruggedness. Intensity of use was positively associated with elevation and an index of prey density. Our results demonstrate non-random space use within the home range and provide new information about previously unstudied non-migratory behaviors of coastal breeding peregrines in Humboldt County, California