A population study of the Blue-breasted Fairy-wren, Malurus pulcherrimus, at Dryandra, Western Australia

Abstract

Over the years 1990–99, a colour-banded population of Blue-breasted Fairy-wrens, Malurus pulcherrimus, was studied at Dryandra State Forest in Eucalyptus wandoo woodland. Much of this work coincided with a study (by other workers) of the same species in patches of heathland scattered through wheatland at Wyalkatchem (1993–98). At Dryandra, groups of 2–4 adults lived all year round in territories averaging 2.5 ha; clutch size was two or three eggs (mean 2.8), with more two-egg clutches laid in dry years, as at Wyalkatchem. The main difference between the two studies was in the timing of breeding. At Wyalkatchem the first clutches were laid in early August, whereas in Dryandra August is still cold, and no eggs were laid before mid-September. In wetter years laying ceased at Wyalkatchem towards the end of December but at Dryandra it continued into February. Individual nest success was low at both sites, but with a longer nesting season Dryandra groups renested more frequently and produced more fledglings (1.63 fledglings per group at Wyalkatchem, 1.93 at Dryandra). Annual survival of adults at Dryandra was c. 5% lower than for the Wyalkatchem birds, which suggests that the habitat for the species at the western edge of its distribution is sub-optimal. As at Wyalkatchem, productivity was at or above replacement level only in years of above-average rainfall. Since productivity at both sites was significantly reduced in drier years, the effect of forecast global warming causes concern for this species. Comparisons between M. pulcherrimus and the Red-winged Fairy-wren, M. elegans, illustrate how the group-living social organisation basic to all Malurus spp. can differ greatly between species as a result of differences in survival and productivity.