Prairie falcon takes white-throated swift in flight

摘要

Breeding success of prairie falcons (balco mexicanus) has been monitored over the past 14 years (ca. 10,000 observation hours) at Pinnacles National Monument (36 deg 29 min N, 121 deg 11 min W), 240 km south-southeast of San Francisco, California. The present account is the only instance of predation on a swift at this site by this species; it details a method of pursuing and capturing avian prey under circumstances that differ from other reports of foraging behavior in prairie falcons and represents one of the few instances of predation on swifts by any species of falcon to be witnessed. My observation attests to the versatile aerial abilities of prairie falcons, which typically use low, flushing-type flights or downward stoops (e.g., White, 1962; Enderson, 1964; Squires et al., 1989) to capture mammals and ground dwelling birds. I was observing a prairie falcon eyrie on 12 May 1996 when, at 1410 h, an adult falcon flew into the eyrie with a small California ground squirrel (Spermophilus beecheyi) that was fed to 3 of 5 nestlings. The adult left the eyrie at 1421 h, circled, gained approximately 100 m of altirade, and dove toward a group of 5 white-throated swifts (Aeronautes saxitalis) in a lowangle, tail-chase. The 1alcon approached the closest swift until it was slightly underneath its intended prey. As the swift began to climb steeply to avoid capture, the falcon rolled over just below the swift and reached up with its talons and grabbed its prey. The fhlcon righted itself, flew back to the nest with the swift, and fed the 2 chicks that had not been fed.