Background
Cats are present throughout Victoria, as domestic pets, free-living strays, or as truly feral animals. Estimates in all these categories suggest that there are well over one million cats in the State.
Cats are obligate carnivores, that is, they must feed on animal protein. Each cat requires a minimum of 100-150g of protein each day, more if a female is nursing a litter. This means that an equivalent of at least seven small mammals, such as native Bush Rats, must be eaten each week by each cat.
Even cats that are well fed, apparently contented pets, will instinctively hunt and kill living creatures. An average of 32 wild animals may be killed by each pet cat every year. Each feral cat can kill many more. The potential impact on wildlife is enormous.
What impact do cats have on wildlife?
Cats are known to kill and eat more than 100 native Australian species of birds, 50 mammals, 50 reptiles, three frogs and numerous invertebrate animals. As more knowledge is obtained more animals continue to be added to the list.
Cats are a major threat to wildlife in the bush, where they are common and occur in most habitats, as well as in towns and cities. For example, in 1992, in response to a plague of native rats in south-west Queensland, where the endangered native Bilby survives, feral cat numbers were observed to be at high levels. The Australian Army was called in to assist with control and, to the amazement of wildlife managers, shot 417 cats in four days within 20 km of the Bilby site. Up to six cats were shot out of a single tree in one day! Of interest is that the high cat numbers were on a cattle station on which dingo control was rigourous. Neighbouring stations, with more dingos, had less cats. Cats can survive on water from prey in areas where drinking water is unavailable.
In Australia, cats (and dogs) have no natural predators. The hunting methods of cats are different to native predators, such as quolls, and so native wildlife has few inbuilt defences against cats.
Cats are most active at night, and especially at dusk and dawn. This coincides with the activity periods of much of our Australian wildlife, placing native animals at risk.
Cats kill prey of up to their own body size; most of Australia’s endangered and vulnerable mammals are in this size category.
Cats can significantly control bird populations. Studies in South Australia indicate that domestic cats probably kill the 'standing crop' of birds, (i.e. the same number are killed as are produced each year).
Cats are significant predators on small mammals. In 15 months one wildlife shelter in Melbourne received 272 native mammals with injuries that resulted from cat attacks; 242 of these were Common Ringtail Possums. Almost all died as a result of the attacks.
Cats have also been responsible for the death of at least 25% of all Sugar Gliders registered in the former Wildlife Management Branch (now DSE) collection.
Cat’s mouths can carry bacteria to which wildlife has little resistance, and wildlife that has been injured by cats usually dies - if not from injuries, then from infection.
Cats are the definitive host of the blood protozoan disease Toxoplasmosis which can affect wildlife, sheep and humans. It can cause unco-ordination, blindness, erratic movement and unnatural daytime activity. Toxoplasmosis is often fatal for infected wildlife. It can have effects on reproduction (the disease can cause abortion in sheep and humans). Endangered Eastern Barred Bandicoots are at threat not only through direct predation by cats but from infection with the disease. It probably predisposes affected bandicoots to predation by cats or dogs and to road trauma.
Research into the reintroduction of rare mammals onto mainland Australia has found that, when foxes are controlled, cat numbers increase, continuing the attack on native species. Similarly, because rabbit is a significant part of feral cat diet in many (especially rural) areas, rabbit control without cat control may lead to increased predation on wildlife. Hence, an integrated pest animal control program is essential.
Cats also have an indirect impact on plant pollination by reducing numbers of native birds.
Although habitat alteration and hunting are also important factors, cats have been responsible for the extinction of over 30 species of birds around the world.
Cats have been the cause of decline and extinction of many bird species on a large number of islands including New Zealand, Macquarie Island, Socorro Island (Mexico), Ascension Island, the Kermadec group, Marion Island and many others. There are also records of mammals and reptiles being similarly affected - for example the endemic rodents of the Galapagos are now only found on islands without cats, and in Western Australia at least two species of now-endangered species of marsupial (Banded Hare-wallaby and Golden Bandicoot) have become extinct on the Monte Bello Islands due to cats.
Pet cats kill an average of 16 mammals, 8 birds and 8 reptiles every year. 900 000 pet cats by 32 wildlife each per year = 29 million wildlife.
Feral cats each need to eat the equivalent of seven native bush rats or ten native birds each week. 200 000 feral cats by 10 wildlife by 52 weeks = 104 million wildlife.
Stray cats in cities kill on average 5 wildlife each week. 300 000 cats by 5 wildlife by 52 weeks = 78 million wildlife.
GRAND TOTAL = 211 million wildlife killed by cats in Victoria each year!
On farms
Toxoplasmosis in sheep, spread by cat faeces, can result in abortions, stillborn lambs, and a reduced lambing percentage. It is the most common cause of infectious abortions in sheep flocks in south-eastern Australia. Cats also carry the stock disease Sarcosporidiosis. Sarcocystis infection can result in carcase condemnation at the abattoir. Cats spread these diseases by contaminating pasture, hay and other animal foods with the parasite via their faeces. They in turn are contaminated by eating rodents, birds and wildlife which contain cysts of the parasite. Farmers who wish to avoid the risk to livestock of toxoplasmosis should not let cats near their pastures.
DEPARTMENT OF PRIMARY INDUSTRIES
August 1999
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