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Dryad

Application of photographic ‘capture-recapture’ modelling to estimate recruitment and apparent survival in a long-lived territorial raptor

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Oct 30, 2025 version files 8.09 KB

Abstract

Survival is a life history trait that contributes most to population dynamics in long-lived birds, and the study of individual characteristics is relevant for population conservation. Here we provide information on territorial recruitment and individual replacement in a population of Bonelli’s eagle Aquila fasciata in southeastern Spain based on a long-term photographic capture-recapture 19-year dataset. We also investigated how individual factors such as sex, age, experience and age at first breeding influence the apparent survival of breeding Bonelli’s eagles using Cormack–Jolly–Seber models. An increase in recruitment rates and a decrease in age at first breeding were observed in the breeding population over time. The apparent survival was high, and the reproductive dispersal was very low. The improvement in apparent survival was age-related and higher in females (0.90 for non-adults and 0.92 for adults) than in males (0.87 for non-adults and 0.89 for adults). These findings can be explained by age-related improvements and differences in movement behaviour between sexes during the breeding season, with females being exposed to lower risks from anthropogenic or natural causes. We also found a positive relationship between territorial experience and the probability of apparent survival, with inexperienced female breeding birds having a higher survival than males. Our results showed that immature breeders had a similar survival to experienced or older birds breeding for the first time, suggesting that age at first reproduction is controlled by reproductive restraint. Our results provide demographic information that improves the understanding of the population dynamics of the long-lived territorial species, and their estimation has important implications for the management and conservation of Bonelli’s eagle populations.