Demography of population recovery: survival and fidelity of peregrine falcons at various stages of population recovery.

Abstract

Factors influencing vital demographic rates and population dynamics can vary across phases of population growth. We studied factors influencing survival and fidelity of peregrine falcons in south Scotland-north England at two stages of population growth: when the population was recovering from pesticide-related declines and density was low, and when it had largely recovered from pesticide effects and density was high. Fidelity was higher for: adults and subadults than for juveniles, females than for males, and juveniles and adults during the low-density than during the high-density study period. Survival was age specific, with lower survival for juveniles than for older birds (juveniles, 0.600 ± SE 0.063; subadults, 0.811 ± 0.058; adults, 0.810 ± 0.034). Furthermore, there was some evidence that survival was generally lower for all age classes during the low-density period than during the high-density period, possibly due to a chronic, persistent effect of organochlorine pesticides as the population recovered. Evidence for a density-dependent effect on survival was weak, but a negative effect of density on fidelity of juveniles (dispersing age class) during the recovery phase suggests density-dependent dispersal when the population was increasing. Our results show how population density can influence demographic parameters differently and how such influences can vary across phases of population growth.