Long-term monitoring reveals sex- and age-related survival patterns in griffon vultures

Abstract

Survival is a key demographic parameter for long-lived bird species as it strongly influences their population dynamics and persistence. In recent decades, several studies have focused on unravelling differential patterns of survival by sex or age in bird populations, as each group may be affected by different ecological and anthropogenic pressures. Vultures are a highly threatened group of birds where age- and especially sex-dependent survival patterns have been understudied, and therefore, obtaining robust estimates and understanding which factors modulate them is crucial for developing management and conservation strategies. Here, we used a long-term dataset (1990–2023) from a wild colony of griffon vultures Gyps fulvus in central Spain and a capture-mark-recapture framework to address potential sex- and age-mediated patterns of apparent survival and resighting. Resighting probabilities were lower for individuals in their first year of life than for older individuals. Apparent survival probabilities increased with age and were generally higher for males than for females, particularly in subadults. Disentangling whether an unequal survival between sexes is due to female-biased dispersal or to true mortality is necessary to understand population dynamics and to be able to implement adequate conservation management actions. Our research underlines the importance of considering sex and age interactions in demographic analyses of long-lived, usually threatened species.