Breeding biology, reproductive success and survival of blue-breasted fairy-wrens in fragmented habitat in the Western Australian wheatbelt

We studied blue-breasted fairy-wrens, Malurus pulcherrimus, over a 6-year period in 17 differently sized remnants in a highly fragmented agricultural landscape at Wyalkatchem, Western Australia. The wrens lived in groups of 2-5 adults, comprising one breeding female, her consort and up to three helpers (usually adult male offspring). Groups lived in permanent year-round territories averaging 2.2 ha. Data from 536 nests indicated that breeding extends from August to December in good seasons but from August to October in years of drought. Overall, the average clutch size was 2.91 (median 3), although in the driest year of the study it was 2.31 (median 2). Individual nest success was low, with a mean of 1.02 fledglings produced per clutch. However, the wrens made 1.87 nesting attempts per year, thereby raising the annual reproductive output to 1.63 fledglings per group and 0.49 potential breeders per group. There was a positive relationship between nest predation and remnant size and no difference in the predation rate of nests in the largest remnant depending on how far they were located from the edge of the remnant. Nest parasitism by Horsfield's bronze-cuckoo, Chrysococcyx basalis, was also positively related to remnant size. Consequently, annual reproductive success was higher in the 13 small remnants (2.16 fledglings per group per year), compared with 3 medium-sized remnants (1.94) and the largest remnant (1.32). Annual adult survival was 63.9% for breeding females and 67.2% for senior males. Survival was positively related to remnant size for adults, but not for fledglings. The annual survival of adults in small remnants was 54.5%, compared with 64.9% in medium-sized remnants and 68.6% in the largest remnant. It is suggested that, in order to conserve sedentary species living in fragmented habitats, we should try to retain the whole range of patch sizes that remain, even if some (or most) of the vegetation mosaic has been removed and even if some remnants are extremely small.