Survival of fledgling Ferruginous Hawks in northern Montana

Abstract

Few data exist regarding survival of Ferruginous Hawks (Buteo regalis) during the fledgling period. Consequently, we estimated the survival rate of juvenile Ferruginous Hawks from fledging to dispersal from the breeding area in northern Montana in 1993 – 1994 using radiotelemetry. A 171-km2 study area contained 24 occupied breeding sites in both years (7.12 km2/pair). Mean productivity was 0.96 young fledged per occupied breeding site (SE = 0.19, n = 48) and 2.30 young fledged per successful nest (SE = 0.21, n = 20). The average fledging age was 43.3 days. The survival rate for 27 radio-marked fledglings was high during the 3 weeks after fledging (Ŝ = 0.86, SE = 0.02). No fledgling mortality occurred > 10 days after fledging. When fledgling mortality was considered, occupied breeding sites produced an average of 0.82 dispersing young (SE = 0.24) and successful nests produced an average of 1.96 dispersing young (SE = 0.18). Our data concur with smaller data sets from earlier studies, which suggested that postfledging mortality is low.