The availability and dimensions of tree hollows that provide nest sites for cockatoos (Psittaciformes) in Western Australia

Abstract

A 15-ha plot of salmon gum woodland contained 241 hollows with an entrance diameter and depth exceeding 90 mm, in 173 trees, the majority (95%) in salmon gums. Occupancy of these hollows during the spring of 1978 was 47%; eight species of bird (six Psittaciformes, one Anseriformes and one Falconiformes) were involved. Galahs, corellas, red-tailed black cockatoos and Port Lincoln parrots were the most numerous hollow-nesting birds in the area; there were differences in the sizes of hollows they used, which were separable on entrance size and on inside diameter of the hollow 0.5 m below the entrance. There was a trend for hollow size to decrease in the order: red-tailed black cockatoos, corellas, galahs and Port Lincoln parrots. Red-tailed black cockatoos nested in more dead trees, or trees which were lower and had smaller canopies, than did the other three species. The woodland contained few young trees, trees were dying rapidly and there was no regeneration. This situation is typical for woodland throughout the agricultural area, and future prospects are discussed.