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Evaluation of a Decline in Population of the Koala, Phascolarctos cinereus (Goldfuss) in Ventnor Reserve, Phillip I., Vic., by means of a Triple-Count Technique

Keith R. Every

16 Valley Road, Mount Waverley, Vic. 3149.

A decline in the koala population on Phillip I , has been evident for some time. This study, in an area set apart from public access, quantifies some aspects of this decline. A triple-count technique for a closed population model, with the freedom that the probability of sighting can vary between the surveys, was used to obtain an estimate of the population within a 65-ha study area. The initial population, in June 1980, was estimated to be 117; this declined to 62 in 3.5 years, during which period 23 deaths and 24 births were recorded. The decline, which averaged 16 koalas per year, is discussed in terms of the low birth rate, of dispersal, and of the contribution of predation by dogs to the death rate.