Breeding chronology, molt, and measurements of accipiter hawks in northeastern Oregon

Abstract

Nesting Northern Goshawks (Accipiter gentilis), Cooper's Hawks (A. cooperii), and Sharp-shinned Hawks (A. striatus) were studied in the Blue and Wallowa mountains of Oregon from 1974 to 1979.Other reports on accipiters from this study evaluated pesticide residues (Henny 1977), nest site characteristics (Moore and Henny 1983), and breeding age of Cooper's Hawks in relation to productivity and nest-site characteristics (Moore and Henny 1984).We describe in this paper the approximate date clutches were completed for each species and age class.Molt and feather growth overlap extensively with breeding, and we discuss this phenomenon relative to breeding stage.We also provide measurements and weights of breeding birds.Reynolds and Wight (1978) presented data on initiation of incubation for accipiters in Oregon, but published data on other parameters during the nesting season were not available.Newton and Marquiss (1982) provide the only detailed molt study for accipiters with their investigation of the European Sparrowhawk (A. nisus).Accipiter weights and measurements during migration in Wisconsin (Mueller et al. 1976, 1979, 1981) provide comparative data.STUDY AREA AND METHODS The study was done within and around Wallowa-Whitman National Forest between 45 and 46 north latitude at 500-1600 m elevation in the Blue Mountains province of Oregon.Franklin and Dyrness (1973) and Hall (1973) describe the physiognomy of this province and climatic conditions of the various forest types.An egg was collected for pesticide analysis from each nest with 2 or more eggs.To estimate when clutches were completed, we used embryonic development of the sample egg, and criteria such as hatching dates and size of young; dates could not be estimated for all nests.Following Reynolds and Wight (1978), we assumed the incubation period for all 3 accipiters was 31 days; the nestling period for Northern Goshawks was 37 days, Cooper's Hawks 30 days, and Sharp-shinned Hawks 24 days.