A Contribution to the Natural History of the Slender-billed Thornbill Acanthiza iredalei in Western Australia

Abstract

Five territories of the Slender-billed Thornbill Acanthiza iredalei were located at Bush Bay south of Carnarvon, Western Australia, and observations on the breeding biology, foraging habits and habitat of nine individual Thornbills were made between 25 and 30 July 1999. These Thornbills occupied pair territories within which they foraged for insects and spiders. Most prey (-90%) was taken by gleaning foliage in samphire and Acacia shrubs. All territories were associated with tidal samphire flats, but the Thornbills also used neighbouring Acacia shrublands. All three nests were placed in samphire shrubs, and only the female brooded. A clutch-size of three was inferred from the number of nestlings. The female was the primary feeder of nestlings, at least during the first week after hatching. We attribute decline of the Slender-billed Thornbill to overgrazing and changed fire regimes affecting vegetation communities adjacent to the samphire flats and saline areas with which the species is associated in Western Australia.