Contrasting long-term trends in age-specific survival of Peregrine Falcons (Falco peregrinus) in Britain using smoothed estimates of recovery probabilities

摘要

Peregrine Falcons Falco peregrinus are an iconic species of long-standing conservation concern as a result of historical patterns of persecution and dramatic pesticide-related population declines in many populations during the second half of the 20(th) century. Although the role of reduced productivity in these declines is well known, the temporal patterns in survival are much less well characterized. We estimate survival probabilities for Peregrines in Britain in the period 1975-2018 from reports of ringed birds found dead, using a non-parametric smoothing spline to account for non-linear temporal variation in recovery probabilities. During this time the population increased from around 350 pairs to 1628 pairs. There was little evidence of a temporal trend in the survival probabilities of adult birds since the mid-1970s, but survival of first-year birds appears to have decreased. Our estimates suggest that increases in the breeding population are further limited by unreported sources of mortality or by density-dependent processes, highlighting the need for better data on immature survival and recruitment. Modelling recovery rates using a spline, rather than independent annual values, improved estimation efficiency with lower credible intervals obtained for the adult annual estimates.