Partial Loss of Red-Tailed Hawk Territories to Swainson's Hawks: Relations to Habitat

Abstract

Of a population of 33 pairs of Red-tailed Hawks (Buteo jamaicensis) inhabiting north-central Oregon, 9 and 10 pairs lost portions of their breeding territories to later-arriving Swainson's Hawks (B. swainsoni) in 1977 and 1978, respectively. The loss was accompanied by aggressive Swainson's Hawk behavior and vigorous Red-tailed Hawk defense. Analysis of the habitat relinquished by Red-tailed Hawks showed perch availability to be an important resource in the habitat relations of these species. Red-tailed Hawks abandoned areas with perches at moderate densities (0.3-0.6 perch/ha) more often than expected by chance while preferentially retaining areas with greater perch densities. The habitat lost by Red-tailed Hawks is associated with high reproductive performance.