MORTALITY OF PRAIRIE FALCONS DURING THE FLEDGING-DEPENDENCE PERIOD

We monitored the survival of 152 radio-tagged Prairie Falcon (Falco me xicanus) nestlings from 37 broods through the hedging-dependence perio d in southwestern Idaho during 1992 and 1993. Mortality rates were hig h but consistent between years, 28% in 1992 and 34% in 1993, despite a significant decline in the primary prey of falcons in 1993. Predation by Great Horned Owls (Bubo virginianus) was the primary cause of mort ality. To a lesser extent, mortality was influenced by the presence of hematophagous ectoparasites (Haematosiphon inodorus) in aeries. We we re unable to find or show an effect of parental behavior (territory at tendance and prey delivery rates) during the late brood-rearing period , hatching date, brood size or fledging mass on mortality. The frequen cy of predation in our study may have negated or diminished the influe nces of these factors. Survivorship was lower during the fledging-depe ndence period than during the incubation or nestling periods.