The Population Dynamics of Red and Western Grey Kangaroos in Arid New South Wales, Australia. I. Population Trends and Rainfall

Abstract

(1) Red and western grey kangaroo populations were monitored on Kinchega National Park and some adjoining sheep stations on a quarterly basis between 1973 and 1981. Kangaroos inside the Park were constrained whilst those outside were not. (2) The years 1973-1976 experienced exceptionally high rainfall providing kangaroos with a superabundance of food. The preceding years were marked by the late 1960's drought and low kangaroo densities, and the following years by average rainfall and high kangaroo densities. (3) The kangaroo populations exhibited two general trends in relation to the exceptional and average rainfall years: a rapid rise and an asymptote. The average exponential rates of increase (r) between 1973 and 1977 were 0.36 p.a. and 0.27 p.a. respectively for red and western grey kangaroos inside the Park; and 0.44 p.a. for both species outside. However, these rates were not significantly different. Since 1978 all populations had a zero average rate of increase and the high densities were maintained. (4) There was no significant difference between the population dynamics of the kangaroos inside the Park and on the adjoining sheep stations, regardless of densities being 2.5 times higher on the Park. It is hypothesized that competition for food by sheep suppressed kangaroo densities outside the Park. (5) The exponential rate of increase (r p.a.) of all populations was positively correlated with lagged rainfall. (6) Rainfall and rate of increase of both species inside the Park exhibited regular trends on time. The regularity was strong for the western grey kangaroo but weak for the red kangaroo.