Species
Feral cat (Felis catus)
Cats have long been associated with humans and under their influence, cats have been distributed throughout most of the available habitats in the world including many uninhabited islands. They were first brought to Australia and New Zealand by European settlers during the 18th century. However, cats may have arrived earlier via the trading routes from south-east Asia, shipwrecks or visits by European ships, especially on Australia’s west coast. During the 19th century, cats were deliberately released in Australia in a misguided attempt to control rabbits, rats and mice. Feral cats now are widespread throughout Australia and New Zealand ranging from the tropics to southern oceanic islands, such as Macquarie Island from where they were recently eradicated.
There is clear evidence that feral cats have caused the decline and in some cases the extinction of native wildlife on islands as well as being a major factor in unsuccessful attempts to re-introduce small mammals on the mainland. This is especially so in New Zealand where there are few natural predators and native wildlife have poor behavioural and other mechanisms to defend themselves from introduced mammalian predators such as cats and stoats. However, well quantified evidence of their impact on native wildlife on the Australian mainland is lacking.
Feral cats have occupied tropical Australia, Tasmania and Kangaroo Island for well over 100 years but there have been virtually no extinctions of native animals on which feral cats prey in these areas. Feral cats may become an important factor when other factors such as land clearing and other forms of large-scale habitat degradation have restricted remaining populations of native wildlife to small island populations.
Feral cats also carry diseases such as toxoplasmosis and sarcosporidiosis which can be transmitted to and cause serious illness and death in native wildlife, stock and humans.
Feral cats are mainly nocturnal and require large amounts of fresh animal protein to successfully survive and reproduce. Inadequate diet is considered to be a major factor regulating their population. Ideally they prefer live animal food although they will take some carrion and refuse at tips. Cats can have two litters a year, averaging four kittens a litter. Few survive to become adults but those that do are weaned at 8 weeks and become sexually mature at approximately 12 months. The major diet is small native and exotic mammals but they also take birds, lizards and insects. Rabbits are a major dietary item in much of Australia.
Feral cat populations appear to be self-sustaining and stray and domestic cats probably play little or no role in maintaining the feral population.
Feral cats have been eradicated from some relatively small offshore islands through intensive effort. However, eradication from the mainland of Australia and the main islands of New Zealand is not possible due to the lack of suitable techniques and the enormous cost. Available techniques such as trapping are very labour intensive and feral cats readily become trap-shy and are wary of ground baits. Being nocturnal, wary and sparsely distributed, shooting is also relatively ineffective for large-scale management. Even when an area is treated, cats can readily recolonise an area. Erection of barrier fences, especially at the neck of peninsulas, combined with intensive control in an adjoining buffer zone has been one of the most effective management strategies.
Modifying components of the habitat to make it less suitable for cats and more suitable for native wildlife may help. This can include reducing fragmentation by rehabilitating tracks and clearings and making it more structurally complex to provide wildlife with greater resources and more places to escape feral cats. Viruses such as feline parvovirus and feline enteritis have been suggested as control methods. However, surviving cats readily become immune to the viruses and studies have shown that there is widespread immunity to feline parvovirus in Australian feral cats. Fertility control has also been suggested but this is only likely to be useful in the peri-urban area where cats more likely to take baits containing the fertility agent.
