Social constraints limit dispersal and settlement decisions in a group-living bird species

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Abstract
Dispersal is a fundamental process affecting the genetic structure of populations, speciation, and extinction. Nevertheless, our understanding of the evolution of dispersal is limited by our paucity of knowledge on dispersal decisions at the individual level. We investigated the effect of interactions between residents and juvenile dispersers on individual dispersal and settlement decisions in Siberian jays (Perisoreus infaustus). In this group-living bird species, some offspring remain on the parental territory for up to 3 years (retained juveniles) whereas other offspring disperse within 2 months of fledging (dispersers). We found that retained juveniles constrained settlement decisions of dispersers by aggressively chasing dispersers off their territory, resulting in dispersers continuing to disperse and settling in groups without retained juveniles. Experimental removal of male breeders during the dispersal period also demonstrated that dispersers were unable to settle in high-quality breeding openings, which were instead filled by older nonbreeding residents. Rather, dispersers immigrated into groups without retained offspring where they became subordinate group members, queuing for a breeding opening. Also, they preferably settled in groups with short queues where no same-sex juveniles were present. Dispersal did not inflict a cost to dispersers through increased mortality. However, the presence of immigrants was costly for breeders because it increased the rate of conflicts during the breeding season which negatively affected nestling condition. These results demonstrate that resident individuals constrain both dispersal and settlement decisions of dispersers. Social interactions between residents and dispersers can thus be a key factor to understand the evolution of dispersal.