TRANSFER EXPERIMENTS OF SEYCHELLES WARBLERS TO NEW ISLANDS - CHANGES IN DISPERSAL AND HELPING-BEHAVIOR

Young of the cooperatively breeding Seychelles warbler, Acrocephalus s echellensis, frequently remain on their natal territories and act as h elpers. Independent reproduction may be constrained by habitat saturat ion (a shortage of breeding territories) or, alternatively, individual s on good territories may achieve higher fitness by staying and helpin g than by dispersing and breeding on inferior territories. Transfers o f warblers to unoccupied islands showed that both habitat saturation a nd variation in territory quality dramatically affected the frequency of delayed dispersal. At first there was no cooperative breeding, but as all high-quality areas became occupied, young birds hatched on them began to stay as helpers, rather than occupy breeding vacancies on lo wer quality territories. However, as the number of helpers on high-qua lity territories increased, thereby reducing the helper's indirect com ponent of inclusive fitness benefits from staying at home, it paid som e helpers to leave, even to poor territories. Thereafter, young reared on poor territories did better to leave to breed on poor territories, rather than stay at home.