Population ecology of western grey kangaroos in a remnant of wandoo woodland at Baker's Hill, southern Western Australia

Abstract

A subpopulation of western grey kangaroos (Macropus fuliginosus) living in a 305-ha remnant of wandoo woodland in the mediterranean climate of the south-west of Western Australia was studied for 10 years. Measurements and estimates were made of a wide range of population characteristics including population size, composition, reproductive rate, emigration and immigration rates and death rates. Growth rates of males and females were established and yearly differences in nutritional status assessed. The population increased over four years from 146 ± 22 to a plateau of around 200 before being culled to 95. The numbers then increased slowly over another six years to 158 individuals. The population had an average of 46 adult males per 100 adult females. Subadults plus juveniles made up 10-36% of the population, depending on the year. Breeding was seasonal, being earlier in years with early autumn rain. Reproductive rate was higher, overall, in these years. Females became sexually mature at about 16 kg, their reproductive rate increased with weight until they reached 24 kg; 91% of adult females over 24 kg had pouch young annually. Mortality of young appeared to be high, and to be the factor regulating the population. On average, only 27% of young survived the first year after leaving the pouch. Emigration rate was estimated to exceed immigration by 5% per annum. The estimated mortality rate of adults was 5% per annum. The nutritional status of individuals varied from year to year; within a year, only females were heavier in early summer than in later summer. It was concluded from faecal nitrogen levels that nitrogen was not a major factor influencing nutritional status in summer. Fifteen years after this remnant woodland was established by clearing, the subpopulation of kangaroos living in it appeared to be relatively stable in numbers, and certainly was not showing the marked fluctuations known to occur in semi-arid areas of Australia.