Feral Animals of the Northern Territory
Feral Cat - Felis catus
Impacts
Feral cats are a serious threat to biodiversity conservation in Australia. Predation by feral cats is appropriately listed as a key threatening process under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act). Feral cats can potentially impact upon native fauna in three ways: through direct predation, through competition and/or through disease.
Direct Predation: Strong evidence suggests that feral cats have played a significant role in the demise and extinction of native fauna, particularly in central Australia. To date, 63 species of native vertebrate have been identified in the stomach contents of feral cats from throughout the Northern Territory including mammals, reptiles, birds and amphibians.
Competition: Evidence to show the effects of competition between feral cats and native species is lacking. However, if competition does occur it is most likely to involve species which are ecologically similar to cats and overlap with cats in their use of food, habitat, shelter and other resources. In the Northern Territory, this would include the carnivorous western quoll (Dasyurus geoffroii) and northern quoll (D. hallucatus). The former is presumed to be extinct in the Northern Territory.
There is also evidence that competition can occur at times between cats and predatory birds. Cats could also reduce prey for diurnal species of raptors such as the brown goshawk (Accipiter fasciatus) and the peregrine falcon (Falco peregrinus). As some larger reptiles such as elapid snakes and goannas prey on a range of vertebrates similar to those taken by feral cats, it is also conceivable that competitive interactions could occur between these groups. Despite such possibilities, there has been no research indicating the existence of competition between cats and reptiles.
Disease: Cat vectored diseases can be transmitted to native animals and to humans. Toxoplasmosis (caused by Toxoplasma gondii) has been recorded in several dasyurid species although its impacts at the population level are unknown.
Background
The origin of feral cats in Australia has been the subject of much speculation. However, current evidence suggests that cats first arrived on the east coast with European settlers in 1788. Feral cats have been present in the Northern Territory for over 100 years, and have adapted to all habitat types.
Distribution and Habitat
We don’t know how many feral cats are in the Northern Territory - they are secretive, cryptic, largely nocturnal and hard to catch which makes it difficult to monitor populations, especially over large areas. Available data indicate that feral cat populations fluctuate markedly in time and space.
Feral cats occupy all habitats ranging from rainforest to desert throughout the Northern Territory. Occupation by cats of arid regions has apparently been facilitated by their ability to survive without drinking. They have efficient kidneys and obtain most of their moisture requirements from the live prey they consume.
Densities can be high in some areas when conditions are favourable. During 1994, for example, the density of feral cats on the Barkly Tableland during an eruption of the long-haired rat, Rattus villosissimus, was estimated at 6.3/km2. In arid areas population densities of about 0.2/km2 are more typical.
Male feral cats in the mulga woodlands of central Australia live in large territories approximately 2210 ha in size. However, in the tropics and in areas with rabbits, home ranges are likely to be much smaller.
Management
Although feral cats have been eradicated from islands using a combination of techniques, broad scale control on the Australian mainland has proved problematic. Because feral cats rarely scavenge, it appears that successful control can only be achieved by distributing poisoned baits at times of low prey abundance. A problem associated with controlling feral cats with toxic meat baits is their impact on non-target species including dingoes which are protected in the Northern Territory.
The management of feral cats is a difficult and often emotive issue. Although they are susceptible to 1080 poison, feral cats do not readily accept baits unless they are nutritionally stressed. This makes broad scale control difficult to achieve under most circumstances.
The Northern Territory Government is in the process of developing a management program for cats on islands.
