Invading together: the benefits of coalition dispersal in a cooperative bird

Abstract

Dispersal attempts can be costly and may often end in failure. Individuals should therefore only disperse when the benefits of dispersal outweigh the costs. While previous research has focussed on aspects of the individual that may affect dispersal success, social factors may also influence dispersal outcomes. One way of achieving successful dispersal could be through cooperative, or coalition dispersal. I investigated this possibility in the cooperatively breeding Arabian babbler Turdoides squamiceps. I found that coalition dispersal appears to be an effective strategy to ensure the success of dispersal attempts, with coalitions more successful than lone individuals at taking over the breeding position in a new group. Lone dispersal was more costly than coalition dispersal, with lone individuals suffering a greater loss of body mass during dispersal attempts. These results suggest a substantial short-term benefit for this type of cooperative behaviour. There was no evidence for dispersal polymorphism in the population, with no detectable phenotypic difference between dispersers and non-dispersers or those that dispersed as part of a coalition compared with those that dispersed alone.