Home range size and habitat-use pattern of nesting prairie falcons near oil developments in northeastern Wyoming

Abstract

Movements and habitat-use patterns were evaluated for a small population (n = 6 pairs) of Prairie Falcons (Falco mexicanus) nesting near Gillette, Wyoming. A total of 2462 falcon relocations was documented through telemetry. The average (n = 6) harmonic-mean 95%-contour home-range was 69 km2, whereas the average 75% contour was 26.6 km2. The convex polygon average home-range size was 29.4 km2. The average 95% and 75% foraging-area contours, where points less than 500 m from the eyrie were excluded, were 111.8 km2 and 57.4 km2, respectively. The convex polygon foraging area was 74.7 km2. It is believed that the 95% foraging-area contour best represented falcon home ranges as confirmed through field observations. Habitat analyses showed that falcons selected foraging areas near their nest sites, in areas of open grassland, and did not overtly avoid oil wells. Falcons foraged in areas with an oil well density of approximately 1.4 wells/km2. These results suggested that falcons could tolerate low levels of oil development on foraging sites when their eyries were insulated from human disturbances.