The Influence of Group Size and Habitat on Reproductive Success in the Superb Fairy-wren Malurus cyaneus

Abstract

The potential influence of rainfall, habitat quality and group size on breeding success in Superb Fairy-wrens was investigated in a study of 161 nesting attempts by 62 breeding units over five breeding seasons near Armidale, New South Wales. Breeding seasons started earlier, and lasted longer, in years with higher than average rainfall, and resulted in higher seasonal breeding success. Proportionately more four-egg clutches than three-egg clutches were laid in years of higher rainfall. Breeding success was correlated with habitat quality (bramble area per territory) and Superb Fairy-wrens on territories with larger areas of brambles made more nest attempts and fledged more offspring per season than did birds with smaller areas of brambles. Brarnbles appeared to have a cumulative effect on breeding success due to better protection from nest predators. No effect of helpers on breeding success per nest attempt was evident and groups with helpers hatched no more nestlings per egg laid and fledged no more offspring per nestling hatched than did pairs. Groups and pairs did not differ significantly in the number of nesting attempts made or the number of fledglings produced per season although groups tended to re-nest sooner after successful nesting attempts than did pairs. It is suggested that the maintenance of cooperative breeding in Superb Fairy-wrens is not reliant on reproductive advantages arising from the presence of helpers at the nest but may be favoured by variation in territory quality.