Use of tree hollows by Carnaby’s Cockatoo and the fate of large hollow-bearing trees at Coomallo Creek, Western Australia 1969–2013

The loss of hollow-bearing trees and lack of replacements are important issues throughout the world where development of intensive agriculture has resulted in the reduction and fragmentation of natural woodlands. Many species of animal depend on hollows (cavities) for breeding and shelter, and are impacted by these changes. One such species is the endangered Carnaby’s Cockatoo Calyptorhynchus latirostris, an endemic of southwestern Australia, which nests in large hollows in eucalypt trees. Nest hollow selection by a breeding population at Coomallo Creek, in the wheatbelt of Western Australia, was studied from 1969 to 2013. The cockatoos nested in any hollow large enough to access (mean entrance diameter 270mm, floor diameter 407mm and depth 1.24m). Nesting attempts in shallow hollows (1000mm). Breeding females returned to the same hollow they used previously, provided they had been successful in the previous breeding attempt and the hollow was not occupied. During the study, the cockatoos used 252 large hollow-bearing trees. By 2013 40% of these had fallen or been pushed over, had been burnt deliberately or by wildfire, or had been damaged such that they were no longer suitable for use by the cockatoos; an average annual loss rate of 0.91%. Based on this rate of loss, only 29% of large hollow-bearing trees standing in 2013 will be extant in 2125 and not all of these can be expected to offer useable nest hollows. The conservation implications arising from the results of the study are discussed.