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

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.