Apparent survival and population turnover in a long-lived generalist raptor: A comparison of estimation methods

Abstract

Adult survival and turnover rates are often estimated in long-lived species as the primary drivers of population dynamics. Various methods have been used, yet comparison of estimation methods is seldom undertaken. To address this gap, we used colour-ringing across different age groups, as well as GPS-tracking and genetic analysis of shed feathers, to estimate these critical parameters in a population of a medium-sized bird of prey, the Lesser Spotted Eagle. According to the colour-ringing data, the apparent survival during the first year of life (0.21) was more than four times lower than that of birds older than one year (0.88); the GPS-tracking (0.84) and genetic analysis (0.81) yielded similar survival estimates. However, population turnover rates derived from genetic feather analysis (0.17–0.43) exceeded expectations based on apparent survival estimates, as well as those derived from colour-rings (0.05–0.17) and GPS-tracking (0.05–0.08). Notably, all markers indicated high site fidelity among adult eagles, with breeding dispersal events being infrequent. Our findings underscore the utility of various methods for estimating apparent survival, though the ecological characteristics of the species may influence the efficacy of each method. However, estimates of population turnover rates were notably influenced by the choice of method and should be interpreted cautiously before recommending management actions.