Relationship between bird-unit size and territory quality in three species of fairy-wrens (Malurus spp.) with overlapping territories

The relationship between unit size and territory quality and size was examined in variegated, superb and red-backed fairy-wrens in an area in which the birds territories overlapped extensively. Variegated fairy-wrens had the least number of paired birds and the largest mean unit size. More than half of the superb and red-backed fairy-wrens occurred in pairs. Territory size did not differ between the species. A positive correlation between unit size and territory size was found only in the variegated fairy-wren. Stepwise regression analyses with backward elimination on 10 habitat variables showed that unit size was associated with different territory-quality measures in the three fairy-wren species. It is suggested that species that are more inclined to form pairs or small groups during the breeding season are also more sensitive to ecological factors and prefer not to form large groups in a resource-limited environment.