Learning on the fly: Rapid development of juvenile shorebirds’ foraging abilities across a migratory range

Learning – the retention of information acquired from experience – is widespread in animals and particularly important in early life. For juveniles, learning about the environments they experience is an essential process that frequently has a social component, but the period over which social experiences influence learning is often unclear. We tested whether juveniles in a migratory shorebird (Black-tailed Godwit) population find prey more quickly when they forage with more adults, at sites spanning their migratory range, and for how long any such effects are apparent. In this population, variation in both foraging environments (habitats, prey) and social environments (access to experienced adults) can occur rapidly throughout the first months of life, which include juveniles’ first migration. We quantified seasonal and geographical variation in size and age composition of flocks, and associated variation in foraging intake rates, of adults and juveniles in flocks at locations across the migratory range (Iceland, UK, Portugal). Intake rates of both ages were lower during the pre-migratory period in Iceland than at non-breeding locations but, while juveniles had significantly lower intake rates than adults in Iceland, there was no age difference after autumn migration. Proportions of juveniles increased during the pre-migratory period in Iceland, and varied between non-breeding locations. Juveniles were found almost exclusively in flocks with adults, but nowhere did intake rates vary with flock size or proportion of juveniles. These findings indicate that, for juveniles, intake rates do not depend on the age structure of flocks they join, but the scarcity of juvenile-only flocks suggests benefits of associating with adults at any frequency, particularly during the pre-migratory period. We discuss these findings in the context of the importance of juvenile development for broad-scale population processes.