Early and accumulated experience shape migration and flight in Egyptian vultures

Two types of experience affect animals' behavioral proficiencies and, accordingly, their fitness: early-life experience, an animal's environment during its early development, and acquired experience, the repeated practice of a specific task.^{1,2,3,4,5,6,7,8} Yet, how these two experience types and their interactions affect different proficiencies is still an open question. Here, we study the interactions between these two types of experience during migration, a critical and challenging period.^9,10 We do so by comparing migratory proficiencies between birds with different early-life experiences and explain these differences by testing fine-scale flight mechanisms. We used data collected by GPS transmitters during 127 autumn migrations of 65 individuals to study the flight proficiencies of two groups of Egyptian vultures (Neophron percnopterus), a long-distance, soaring raptor.^11,12 The two groups differed greatly in their early-life experience, one group being captive bred and the other wild hatched.¹³ Both groups improved their migratory performance with acquired experience, exhibiting shorter migration times, longer daily progress, and improved flight skills, specifically more efficient soaring-gliding behavior. The observed improvements were mostly apparent for captive-bred vultures, which were the least efficient during their first migration but were able to catch up in their migratory performance already in the second migration. Thus, we show how the strong negative effects of early-life experience were offset by acquired experience. Our findings uncover how the interaction between early-life and acquired experiences may shape animals' proficiencies and shed new light on the ontogeny of animal migration, suggesting possible effects of sensitive periods of learning on the acquisition of migratory skills.