Biology and ecology: Feral and domestic cats are descended from wildcats
(Felis silvestris) native to Eurasia and Africa. Cats share a long history of association with humans that has helped their spread across the globe. Archaeological evidence of cat taming dates back approximately 9500 years ago to Crete. Today, cats can be found on every continent except the North and south poles.
Feral cats have the body shape, acute senses and fine coordination of the ultimate predator.
Feral cats weigh about on average 3–4 kg, with body lengths ranging from 40–60 cm. Males are usually larger than females. Most feral cats are short haired and not showy breeds like Siamese or Persian. Coat colours range between ginger, tabby, tortoiseshell, grey and black. In Australia, tabby and ginger cats are the most abundant, this is all due to breeding in the wild where stealth and camouflage is of great importance in the hunting of prey species.
Breeding: Female cats can reproduce at between 10–12 months of age, with males reaching maturity at about one year. Cats generally do not breed during winter where cold weather can reduce the survival of kittens. They produce up to three litters a year (65 days gestation) averaging four kittens per litter. Kittens are weak hunters and can take up to six months to learn all the necessary skills to become independent hunters. Kittens and juveniles are often killed by foxes, dingoes, large reptiles like goanna’s and wedge-tailed eagles. Female feral cats are likely to reproduce for all of their adult lives. This high reproductive ability keeps populations growing, despite the high death rates of young. Feral cat populations do not need a supply of new domestic or stray cats to maintain their numbers.
Habitat: Feral cats live in a diverse range of habitats including deserts, forests, woodlands and grasslands. They usually reach their highest densities on small islands or in human-modified habitats such as farms and rubbish tips due to the large amounts of food available. However, most of the time they are found in low numbers with relatively large home ranges (may exceed 10 km2). The distance travelled by ranging cats depends on the availability of prey, breeding season of the cat and habitat. Males tend to roam over larger range sizes than female cats. Feral cats are generally nocturnal and will rest during the day in den sites such as hollow logs, piles of debris, rabbit warrens or dense scrub.
Diet: Feral cats are carnivores and can survive with limited access to water, as they use the moisture from their prey. They generally eat small mammals, but also catch birds, reptiles, amphibians, fish and insects - taking prey up to the size of a brush-tail possum. In pastoral regions, they feed largely on young rabbits, but in other areas feral cats prey mainly on native animals. In a 2012 report, the AWC estimates that each feral cat kills between five and 30 animals a day. It says taking the lower figure in that range and multiplying it by a "conservative population estimate" of 15 million feral cats gives a minimum estimate of 75 million native animals killed daily by feral cats.
Current Australian distribution: There is on average one feral cat for every one to two-kilometres square but this may be larger if food supplies are scarce. Cats now occupy 99% of Australia, including many offshore islands.
Economic impacts: The cost of feral cat’s due to management and research has been estimated at $2 million per year. The loss inflicted by feral and domestic cats, based on bird predation alone, has been estimated at $144 million annually.
Environmental impacts: Feral cats are exceptional hunters and pose a significant threat to the survival of many native species including small mammals, birds and reptiles. Feral cats have been implicated in extinctions of Australian native animals and have added to the failure of endangered species reintroduction programs (eg numbat and bilby). About 80 endangered and threatened species are at risk from feral cat predation in Australia according to Australia’s Environment Protection & Biodiversity Conservation Act (1999)
Social impacts: Feral cats pose a serious health risk to humans, livestock and native animals as carriers of diseases such as toxoplasmosis and sarcosporidiosis. Cat-related toxoplasmosis can cause wide ranging health problems from debilitation, miscarriage to congenital birth defects in humans and other animals. Feral cats also represent a high-risk reservoir for exotic diseases such as rabies if an outbreak were to occur in Australia.
Strategies for control
Baiting - In order to kill a cat using poison baits, cats must first find and then ingest the bait, unfortunately cats hunt mainly using sight and sound so finding an inert sausage may be hard for a cat to locate. Many cats fail to find a poison bait before it breaks down and are no longer toxic. Even when cats do find baits, up to 80% of encounters do not lead to bait ingestion, the cats often ignoring, sniffing or avoiding baits when detected. This is because cats prefer to catch their own live prey and will only ingest a bait when very hungry.
Successful baiting relies on using large densities of baits in areas with low food availability at the right time of year when cats are hungriest this being in late autumn to late winter before prey becomes abundant in spring.
Grooming trap- A grooming trap squirts a poisonous paste onto the fur of the cat as it walks past a trap station, which it then ingests through compulsive grooming.
Cage and leghold traps- These techniques are very useful in urban and rural situation; the cage trap is the preferred method for dealing with feral cats as they are quite vicious and lively when caught and this will reduce the likelihood of the animal hurting the operator or itself in the process. This also helps for euthanasia if they are caught in an urban area. Padded-jaw, leg-hold traps should only be used at sites where the animal can be killed by shooting whilst still held in the trap. Leg-hold traps may be more effective than cage traps for hard-to-catch cats that have had minimal exposure to humans.
Ground shooting – Shooting is one of the main methods of controlling feral cats, usually done at night from a vehicle fitted with spotlights.
This method is fairly labour intensive but when done by a skilled operator it can quickly reduce the local numbers of feral cats very quickly. It is most probably the most humane way of control where the right calibre and bullet placement is paramount.
Integrated pest management –
With all the techniques explained above we can see that with an integrated approach the feral cat numbers could be reduces quite quickly if all steps are taken. Traps can be set, baiting programs be used and a night time shooting schedule can be devised, with all these running at the same time as a singular program they will be much more affective together magnifying the effectiveness of each other.