Long-lasting behavioural patterns associated with timing of independence in golden eagles (Aquila chrysaetos)

The development of key behaviours during ontogeny can have long-term consequences for individual fitness. In birds, foraging and energy-efficient flight skills have a strong potential to influence energy budgets and thus body condition. While early acquisition of these skills has been shown to result in early independence, the progression of such behavioural skill differences after independence remains poorly understood. Here, we investigated the development of behaviours in juvenile golden eagles (Aquila chrysaetos) over their first five years of life. We quantified behavioural time budgets using classified accelerometer data collected by biologgers from 46 individuals. We studied changes of behavioural compositions throughout development (early post-fledging dependence phase, late post-fledging dependence phase, dispersal phase), age, season and sex, and we examined the relationship between behavioural composition and the timing of independence (onset of dispersal). We found that overall time spent in flapping flight increased from early to late post-fledging but remained largely constant throughout independence. Time spent soaring, however, continuously increased from the early post-fledging phase to the dispersal phase, while time spent feeding decreased. Notably, dispersal timing strongly influenced flight behaviour after independence: although early and late dispersers spent a similar amount of time flying in their first year post-independence, early dispersers spent considerably more time flying in later years than late dispersers, particularly in soaring flight. In addition, early dispersers also onsistently spent more time feeding compared to their late dispersing peers. Our findings suggest that early dispersing juveniles develop superior flight skills and have higher foraging success throughout their pre-reproductive life which may result in long-term competitive advantages that can improve survival and recruitment success.