Responses to fire of Slender-billed Thornbills, Acanthiza iredalei hedleyi, in Ngarkat Conservation Park, South Australia. I. Densities, group sizes, distribution and management issues

Abstract

The Slender-billed Thornbill, Acanthiza iredalei hedleyi, was studied in recently burnt, regenerating and mature heath (3, 10 and 22 years since fire respectively) in Ngarkat Conservation Park, South Australia. Data collected between 1991 and 2002 demonstrated that densities peaked seven years after fire at 0.26 birds ha^–1, while densities were lower and less variable in unburnt mature heath. Comprehensive searches in spring 2000 confirmed this trend, with densities varying from 0.02 birds ha^–1 in mature heath, to 0.06 and 0.07 birds ha^–1 in burnt and regenerating heath.

Between spring 2000 and autumn 2001 group sizes increased in the recently burnt heath from 4.3 to 6.3 birds per group. However, group sizes did not increase over the same period in the regenerating and mature heaths. Between 1991 and 2002 group sizes did not differ significantly between heaths that had been burnt since 1990 (2.7 birds per group) and mature heath burnt in 1978 (2.7 birds per group).

In the mature heath, Slender-billed Thornbills demonstrated strong fidelity for certain areas and were observed feeding juvenile birds on a number of occasions. This suggests that birds can persist in mature heath, albeit at low densities and in isolated areas of suitable habitat, and that frequent fires are not essential for population persistence. Furthermore, long-term records suggest that recolonisation of recently burnt heath is likely to occur from adjacent unburnt heath and is more successful after smaller fires. Therefore, in order to protect areas from which Slender-billed Thornbills can disperse into recently burnt habitats in Ngarkat, a spatial mosaic of habitats at different stages of post-fire succession is required.