Natal legacies cause social and spatial marginalization during dispersal

Early-life experiences can drive subsequent variation in social behaviours, but how differences among individuals emerge remains unknown. We combined experimental manipulations with GPS-tracking to investigate the pathways through which developmental conditions affect social network position during the early dispersal of wild red kites (Milvus milvus). Across 211 juveniles from 140 broods, last-hatched chicks-the least competitive-had the fewest number of peer encounters after fledging. However, when food supplemented, they had more encounters than all others. Using 4425 bird-days of GPS data, we revealed that this was driven by differential responses to competition, with less competitive individuals naturally spreading out into marginal areas, and clustering in central foraging areas when food supplemented. Our results suggest that early-life adversities can cause significant natal legacies on individual behaviour beyond independence, with potentially far-reaching consequences on the social and spatial structure of animal populations. Early-life conditions can drive the emergence of social behaviour, but the underlying mechanisms are largely unknown. Combining a feeding experiment during development with GPS tracking and social network analysis on 211 red kite Milvus milvus juveniles, we reveal that during dispersal, last hatched have the fewest number of peer encounters, but if food supplemented in the nest, they increase their competitiveness and engage in more social encounters than their peers by clustering in areas of high peer density. Our study suggests that early-life conditions cause significant natal legacies on individual behaviour with potentially far-reaching consequences on the social and spatial structure of animal populations.image