The Nesting Biology of the Chowchilla, Orthonyx spaldingii (Orthonychidae)

Abstract

Fifty-two nests of the Chowchilla Orthonyx spaldingii were examined on the Paluma Range and Atherton Tableland, north Queensland. Nests took from two weeks to several months to be completed. A single egg was laid in a dome-shaped, bulky, stick nest built on the ground (44%) or on sites < 3.3 m above ground. Nesting occurred throughout the year, with peak activity during July–December producing most fledglings (84%) during September–February. Fresh egg weight represented 10.6% of adult female weight. Incubation was 25 days and the nestling period 22-27 days, both being long for a tropical passerine. At Paluma hatching success was 75% and fledging success 67% at those nests where the fate of the egg or nestling was known. Only the female incubated, brooded and fed young, although she was often provisioned by one, or rarely two, male members of her group. Because no group member other than the female parent has been seen to provision the nestling/fledgling, Chowchillas cannot be considered co-operative breeders although all group members help defend the group territory. This aspect of their life history requires further investigation, since the congeneric Logrunner O. temminckiihas been reported once cooperatively breeding.