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 environmental conditions 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 the association between nestling body condition and activity levels (ODBA), the relationship of nestling activity with the timing of fledging and post-fledging activity, and the effects of post-fledging activity on post-fledging movements and the timing of dispersal. We found that nestlings with good body condition also showed increased activity levels. Active nestlings fledged earlier and remained more active after fledging than passive nestlings during early post-fledging. 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 due to early-life conditions. They suggest that early activity phenotypes of nestlings drive the timing of subsequent life-history transitions, thereby representing a key mechanism that links early life conditions with future performance.