Decoupling of emigration timing and skill acquisition in a saturated population of golden eagles

Abstract

Many animals must gain independence from parental care by acquiring skills necessary for survival. Thus, the rate of skill acquisition can predict when parental care ends and animals emigrate. However, young animals sometimes acquire adult-like skills long before they emigrate. We asked why the timing of emigration decouples from the rate of skill acquisition and proposed that skill acquisition may instead link to the timing of excursions from natal territories before emigration. We used global positioning system  tracking of 14–64 juvenile golden eagles (Aquila chrysaetos), which learn to fly and hunt under parental care. We expected flight performance to predict the timing of excursions better than the timing of emigration. Using time-to-event models, we predicted excursion and emigration rates based on flight performance and patterns of daily movement. Contrary to our prediction, flight performance failed to predict either event, whereas daily movement predicted both. Daily movement may capture motivation and weather together with flight skills, and those factors probably drive emigration. Juveniles may delay emigration not because they lack skill, but because the costs of independence outweigh its benefits. This decoupling of ability and choice may also obscure the link between skill acquisition and the end of parental care in other systems.