Distribution of tree-hollows and hollow preferences by parrots in an urban landscape

Abstract

The number of hollow-bearing trees, and associated hollows, in urban habitats continues to decline as cities expand. Remaining hollows may be unsuitable for species of parrot that have specific preferences or requirements for certain characteristics of tree-hollows. To determine the distribution of hollow-bearing trees and tree-hollows in Sydney, Australia, we surveyed 264 sites within parks, streets, golf courses, patches of remnant vegetation and continuous forest. To determine whether species of parrot were associated with specific hollow characteristics, motion-activated video-cameras were installed to monitor use of hollows in remnant vegetation and continuous forest. The number of both hollows and hollow-bearing trees varied significantly among habitats, with all urban habitats having significantly fewer hollow-bearing trees than did continuous forest. There was no significant difference in the number of hollows within remnant vegetation and continuous forest. Hollow visitation by Rainbow Lorikeets (Trichoglossus haematodus), Sulphur-crested Cockatoos (Cacatua galerita) and Australian King-Parrots (Alisterus scapularis) was significantly associated with particular hollow characteristics, most importantly type of hollow, orientation of hollow and species of tree. Knowledge of the distribution of hollow-bearing trees throughout landscapes, as well as the characteristics of hollows that are associated with particular species of parrot, is crucial to conserve populations of hollow-dependent bird species in urban areas.