Impact of Wildfire on the Nesting behaviour of Birds in Heathland

Abstract

This paper describes the effects of wildfire on the nesting behaviour of some species of birds in a heathland community at Gooseberry Hill, Western Australia. The most severe fire during the nine year (1981-89) study was a hot summer burn in January 1985, which destroyed 95% of the study area. In the spring following that fire, 81% of the species previously known to breed in the area were still able to nest. The nesting substrate, height, site and aspect for three of the most abundant species (splendid fairy-wrens, western thornbills and yellow-rumped thornbills) were examined in detail. In the immediate post-fire year, all three used as nest sites only those plant species which regenerate by sprouting. The mean height of splendid fairy-wren nests in shrubs was lower than in unburnt habitat, although the wrens also built some nests in unusually high sites in trees in the first two seasons after fire. The mean height of western thornbill nests did not change but nest placement in a favoured substrate, Xanthorrhoea preissii, varied according to time since fire. Yellow-rumped thornbill nests built in burnt habitat tended to be higher and in a more restricted range of substrates than previously. Breeding of splendid fairy-wrens was delayed by three to five weeks in the first year after fire and the number of nests built per group had almost doubled by the second season. Only 59% of adult female western thornbills attempted to nest in the season immediately following the 1985 fire and the onset of breeding in burnt habitat was up to five weeks later than in unburnt. The delay by splendid fairy-wrens and western thornbills was attributed to a shortage of nesting material and adequate food for egg production, respectively, whereas the increase in the number of nests built by splendid fairy-wrens was attributed to a high rate of nest failure. At least two species (white-browed scrubwren and white-cheeked honeyeater) did not nest for two years after the 1985 fire and Acanthiza apicalis has not nested up to the present time (five years). The fire-modified habitat appeared beneficial to little button-quail and elegant parrot, which nested on the study area only after fire. White-winged triller and dusky woodswallow were more numerous breeders after fire than previously. Our findings highlight the importance of detailed long-term studies for estimating adequate fire-free intervals necessary for the conservation of resident avian species. A minimum period of at least 10 years is suggested for heathlands of south-western Australia.