Translocation of shorebird siblings shows intraspecific variation in migration routines to arise after fledging

Though many recent tracking studies have uncovered considerable variation in the migratory routines of birds, the source of this variation is surprisingly poorly discussed. We hypothesize that a wealth of possible factors, including factors other than genetics, translate into these variable outcomes. To demonstrate how factors that are not inherited can shape migratory routine during development, we performed a translocation and delayed-release experiment with juvenile hand-raised black-tailed godwits Limosa limosa limosa that were carefully matched for ancestral background, releasing siblings 1000 km apart. Translocated juveniles adopted the spatiotemporal pattern of migration that is habitual for the population at the release location rather than the origin. This leads to a rejection of the hypothesis that the migration of inexperienced birds is only shaped by pre-release factors including genes, maternal material in the eggs and a common environment from hatching to fledging. Instead, these findings are consistent with inexperienced migrants also developing their knowledge and capacities through contextual individual learning, the precise nature of which now warrants study. That hand-raised godwits, depending on the context in which they are released, can be induced to show different migratory routines, wintering sites and breeding locations from their siblings, indicates that processes during development offer the substrate for rapid adaptation of long-distance migration.