Occurrence of potential nest trees and their use by birds in sclerophyll forest in north-east Tasmania

Abstract

Abstract Breeding of hollow-nesting birds and the distribution and availability of tree hollows were investigated in an area of sclerophyll forest in north-eastern Tasmania. The occurrence of potential tree hollows was assessed from the ground and used as an index of actual hollows. Entrance size was categorized as small, medium or large corresponding to the differing requirements of the birds present on the site. Smaller hollows were more abundant than larger hollows. The distribution of hollows amongst trees was highly clumped. Diameter at breast height and the presence of a fire scar explained one-third of the variation in numbers of hollows per tree. Streamside and non-streamside areas did not differ in the number of hollows/tree or the sizes of hollows present. Thirty trees were found that were utilized as nest sites by striated pardalotes Pardalotus striatus, laughing kookaburras Dacelo novae- gaineae, green rosellas Platycercus caledonicus and yellow-tailed black cockatoo Calyptorhynchus funereus. In comparison with a representative sample of trees, nest trees were larger, had a greater number of potential hollows, a greater proportion of larger hollows and a greater proportion were fire scarred. Eucalyptus viminalis was used as a nest tree to a greater extent than expected from its relative abundance. Hollows appeared to be far in excess of the requirements of the birds present. Trees remaining in streamside reserves after logging would probably provide enough hollows to support the number of hollow-nesting birds present before logging. However, only 13% of striated pardalotes and none of the other species utilized streamside areas for nesting in the undisturbed forest.