Predation by house cats, Felis catus (L.), in Canberra, Australia. II. Factors affecting the amount of prey caught and estimates of the impact on wildlife

Abstract

Information on the amount of vertebrate prey caught by house cats in Canberra was collected by recording prey deposited at cat owners’ residences over 12 months. The amount of prey taken was not significantly influenced by cat gender, age when neutered, or cat breed. Nor did belling or the number of meals provided per day have a significant influence on the amount of prey caught. The age of the cat and the proportion of nights spent outside explained approximately 11% of the variation in the amount of prey caught by individual cats. In all, 43% of variation in predation on introduced species (predominantly rodents) was explained by distance from potential prey source areas (i.e. rural/grassland habitat) and cat density. The mean number of prey reported per cat over 12 months (10.2) was significantly lower than mean predation per cat per year based on estimates made by cat owners before the prey survey began (23.3). Counts of the amount of prey caught by house cats were highly positively skewed. In all, 70% of cats were observed to catch less than 10 prey over 12 months, but for 6% of cats, more than 50 prey were recorded. Estimates of predation by house cats, particularly extrapolated estimates, should be treated with caution. The total number of prey caught by house cats in Canberra estimated using the sample median was approximately half the estimate based on the sample mean. Predation estimates alone do not prove that prey populations are detrimentally affected, especially in highly disturbed and modified environments such as suburbs. Impacts on native fauna are likely to be most significant in undisturbed habitat adjacent to new residential developments.