Cascading carry-over effects of early activity phenotypes in golden eagles

Early-life conditions are often associated with fitness of animals later in life. Although recent studies show that individual characteristics during development affect the formation of early behavioural phenotypes, we have a limited understanding of the cascade of life-history transitions from early phenotypes to fitness-relevant behaviours in later life stages. Here, we used GPS and body-acceleration data of 35 juvenile golden eagles (Aquila chrysaetos) to investigate factors associated with nestling activity levels (overall dynamic body acceleration; ODBA), the relationship between nestling activity and the timing of fledging and post-fledging activity, as well as the effects of post-fledging activity on post-fledging movements and the timing of dispersal. We found that brood size, but no other intrinsic or extrinsic factors, was associated with activity levels. Active nestlings fledged earlier and remained more active after fledging than passive nestlings.Increased post-fledging activity levels were related to an increased number of pre-dispersal forays and an early timing of dispersal. Even though some effects showed reduced certainty, our results provide evidence for downstream effects of behavioural differences expressed in the nest. They suggest that early activity phenotypes of nestlings drive the timing of subsequent life-history transitions, thereby representing a key mechanism that links behavioural phenotypes in early life with future performance.