Ecology of feral cats on a Tasmanian Island

Hayde, K. A. (1992). Ecology of the feral cat Felis catus on Great Dog Island (Doctoral dissertation, University of Tasmania).

Aspects of the ecology of feral cats on Great Dog Island, Bass Strait, were investigated from May to September 1991. Population structure and dynamics, morphology and phenotypes, condition and gastro-intestinal parasites and diet were studied. A culled sample of 189 feral cats displayed a male: female ratio of 1:1 and indicated a pre-eradication density of at least 56.9 cats/km2• Juveniles and sub-adults made up 44.9% of the population. A breeding season was inferred by kitten age and by changes through time in the population structure. Approximate life expectancy was estimated to be 73-84 months for males and 85-96 months for females. Counting cementum annuli in the teeth was shown to be an effective method of age determination. The length and weight of male and female feral cats of Great Dog Island was comparable to that of feral cats found on the mainland Australian. However, a decline in the weight of females between autumn and winter suggested the occurrence of a seasonal nutritional stress. The relationship between age and length in adult males suggests that greater length offers an advantage to longevity. The presence of seven mutant pelagerelated genes, in addition to the wild type, indicated a comparatively high degree of genetic diversity within the feral cat population of Great Dog Island. The long hair allele is probably being selected against as juveniles suffer high mortality. The expression of the inhibitor allele is bias toward males. No significant relationships were found to occur between coat colour and weight or length. The analysis of gut contents showed that a total of 26 species were ingested: 2 bird, 1 mammal, 5 reptile and 18 arthropod species. The gut of 16 cats were either empty or contained only residual food stuffs. Most cats had soil and plant matter in the gut. There was no evidence of cannabalism and no human refuse was present. It is likely that some artht:opod prey were excavated. There was no advantage in age or body size in obtaining prey species. Generally, the coat skin and tooth condition of cats on Great Dog Island was very good. The nutritional condition (fat deposits) of cats suggested that cats were generally in good condition in autumn. Both males and females underwent a large decline in fat reserves from autumn to winter and reserves were further depleted as winter progressed. This resulted in the general nutiitional condition of the winter cats being poor. Gastro-intestinal parasites present were Taenia taeniaeformis, Toxocara cati and Cylicospirura felineus . Parasite infestation was biased toward females. Loss of condition did not generally result in increased susceptibility to parasite infestation. This was instead better explained as a response to diet and climate.