NESTING HENDERSON REED-WARBLERS (ACROCEPHALUS-VAUGHANI-TAITI) STUDIEDBY DNA-FINGERPRINTING - UNRELATED COALITIONS IN A STABLE HABITAT

Using DNA fingerprinting we studied Henderson Reed-Warblers (Acrocepha lus vaughani taiti), which are confined to Henderson Island in the cen tral South Pacific. During the single study season, the birds had a we ll-defined nesting period from late August to early January. About one -third of nesting groups comprised three, not two adults. The members of trios, which could include two males and one female, or one male an d two females, were unrelated. However, all members of trios contribut ed to incubation and/or feeding the young, whether or not they were pa rents of the chicks. The output of young per adult was slightly but no t significantly higher in pairs than trios. We suggest a compensating advantage for members of trios: in the stable island habitat, young bi rds may be more readily able to secure a nesting territory when belong ing to a trio than when in a pair.