Wintering Sharp-Shinned Hawks (Accipiter striatus) in an Urban Area of Southwestern Idaho

Abstract

During the three winters (1980 to 1984) in Nampa, Canyon County, of southwestern Idaho, 17 sharp-shinned hawks (Accipiter striatus) were trapped, banded and measured at a backyard bird feeder trapping station. Mean mass of 5 females was 172.4 g (range 163 to 185) and mean wirlg chord for 6 females was 201.8 mm (range 197 to 209). Mean mass for 12 males was 103.1 g (range 94 to 115) and mean wing for 18 males was 174.8 mm (range 168 to 180). Five, 6 and 10 sharp-shinned hawks were trapped during the 3 winters with 6 individuals being recaptured during either the same winter (2) or a 2nd winter (4) resulting in 23 captures with additional sightings of marked birds for a total of 29 encounters. Repeat encounters during the same, 2nd, and 3rd winters strongly suggest some winter fidelity for this accipiter in urban areas of southwestern Idaho. Urban bird feeders concentrate prey of appropriate body size in suitable habitat which enhances opportunities for sharp-shinned hawk foraging. The sharp-shinned hawk (Accipiter striatus), smallest and most migratory of the three North American accipiters, is generally regarded as somewhat common throughout the western United States. Although its population trends are not well known outside of Oregon where it is listed as stable (Reynolds 1989), Bednarz and others (1990) reported migration counts indicating the northeastern United States sharpshinned hawk population was stable. Recent unpublished reports suggest declines in the East, but no rigorous analysis has yet to be published (J. C. Bednarz, pers. comm.). In Idaho this species is considered an uncommon breeder (Larrison and others 1967), common transient, and an uncommon and rather local winter resident (Burleigh 1972). Tripp and Powers (1990) recorded a few sharp-shinned hawks on winter car surveys of diurnal raptors in vicinity of Deer Flat National Wildlife Refuge in southwestern Idaho, 1983 to 1986. Otherwise, I know of no published wintering data on this