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-km(2) study area contained 24 occupied breeding sites in both
years (7.12 km(2)/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 durin
g the 3 weeks after fledging (g = 0.86, SE = 0.02). No fledgling morta
lity occurred > 10 days after fledging. When fledgling mortality was c
onsidered, occupied breeding sites produced an average of 0.82 dispers
ing 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 l
ow.