Decline of the urban Koala (Phascolarctos cinereus) population in Warringah Shire, Sydney

Abstract

The Koala population in Warringah Shire has declined over the last 50 years with increasing urbanization. Koalas were reported from various localities throughout the Shire in the 1940's, 1950's and 1960's. They now occur only at Barrenjoey Peninsula. Ku-ring-gai Chase National Park and, possibly, Davidson Park State Recreation Area. The colonies at Barrenjoey Peninsula and Ku-ring-gai Chase National Park have both declined in numbers and distribution since the 1970's. On Barrenjoey Peninsula, the main subject of this study, clearing for residential development has steadily reduced the area of forested land from about 705 ha (47% of the Peninsula north of Bungan Beach) in 1946 to about 125 ha (8%) in 1989. The Koala colony on the Peninsula has declined from an estimated 123+ Koalas in 1970 to only about eight Koalas in 1989. The remaining Koalas appear to use several Council bushland reserves as refuges: Angophora Reserve/Hudson Park, Stapleton Park, Careel Headland Reserve, Crown of Newport Reserve and, until 1988, Algona Reserve. The principal food tree on Barrenjoey Peninsula is Grey Gum, Eucalyptus punctata. Other important food trees are Scribbly Gum, E. haemastoma, and Swamp Mahogany, E robusta. These food trees occur in low densities in the reserves compared with their former densities elsewhere on the Peninsula. The reserves have also suffered extensive eucalypt dieback associated with urban runoff, and their eucalypt communities are threatened by expansion of rainforest vegetation and Black She-oak, Allocasuarina littoralis, scrub. The chief threats to continued survival of the Peninsula's Koala colony are further loss of habitat, within as well as outside reserves, and further mortality from dogs, motor vehicles and the disease chlamydiosis. The limited information available suggests that dogs have been the chief cause of mortality on the Peninsula, in contrast to other urban colonies studied, where it has been motor vehicles and chlamydiosis. The incidence of chlamydiosis has been low but may pose a particular threat to the few remaining Koalas. The history of Koalas on Barrenjoey Peninsula illustrates how a carefully planned and managed reserve system is crucial for Koala conservation in urban areas. This must be established in the early stages of regional development The deficiencies of the reserve system on Barrenjoey Peninsula pose enormous difficulties for rehabilitation of the Koala colony now.