FAIRY-WREN HELPERS OFTEN CARE FOR YOUNG TO WHICH THEY ARE UNRELATED

In contrast to most cooperatively breeding birds, helpers in groups of superb fairy-wrens (Malurus cyaneus) are often not related to the young they provision because frequently their mothers either die or move, and because most fertilizations are gained by males which are outside the group that rear the young. All helpers provision broods, but this care does not enhance productivity when compared to unassisted pairs. Helpers provide care regardless of the degree of relatedness to the young they provision. Therefore, it is unlikely that helping behaviour in fairy-wrens is maintained simply by indirect benefits gained through the production of non-descendant kin. Alternative explanations of care: 'unselected' hypothesis; enhanced Future probability of breeding; and direct increases in reproductive success can also be rejected. Our data support the view that helping is a payment to breeders which allows helpers to stay in the group.