Publications archive - Biodiversity
Key departmental publications, e.g. annual reports, budget papers and program guidelines are available in our online archive.
Much of the material listed on these archived web pages has been superseded, or served a particular purpose at a particular time. It may contain references to activities or policies that have no current application. Many archived documents may link to web pages that have moved or no longer exist, or may refer to other documents that are no longer available.
Biodiversity Group Environment Australia, 1999
0 642 2546339
Eradication of feral cats is often suggested as an attractive option because, once achieved, it requires no further commitment of resources other than for monitoring. Bomford and O’Brien (1995) argue that the following conditions must apply to achieve eradication:
They further state that it is the preferred option only when:
These conditions cannot be met for feral cats on mainland Australia or in Tasmania at present. Eradication of feral cats is well beyond the capacity of available techniques and resources because the species is so well established across such a vast area. In contrast, eradication of a population of feral cats from an island may be feasible provided a persistent campaign can be mounted (Veitch 1985).
Historically, a range of techniques has been used in attempts to control feral cats, including shooting, trapping, poison baiting, fumigation and hunting. Control techniques, both those currently available and those being developed, are briefly reviewed below. Available methods are generally expensive, labour intensive, require continuing management effort and can be effective only in limited areas.
Feral cats have been hunted for their fur, which was mostly exported, but no skins or furs have been exported since 1988-89 (Ramsay, 1994). This export was low volume and subject to fluctuations according to the value of skins (Ramsay, 1994). Commercial hunting will only harvest a target species as long as it is commercially viable to do so. Social considerations also strongly influence such activities, even when commercially viable. Where the desired benefit of commercial harvesting is the protection of threatened species from predation, market variability is unlikely to result in controls being applied in a consistent manner.
Newsome et. al. (1989) found that rabbit numbers increased significantly in areas where feral cats and foxes were systematically removed by spotlight shooting, and demonstrated that systematic spotlight shooting of predators is a method for managing some endangered species in appropriate habitats. As a control technique its value lies in being applied for an extended period, or being timed to take advantage of opportunities that expose feral cats to such control actions, eg. wet season flooding.
Feral cats are killed by recreational shooters but the magnitude of the impact on feral cat or prey populations is unknown. The South Australian Department of Environment and Natural Resources uses recreational hunters for controlling feral goats and to complement other methods of fox and feral cat control in some areas (T. Naismith pers. comm.). Their use is regulated by a code of conduct and collectively by the hunters as a club.
In identifying shooting, when carried out humanely, as an acceptable control technique, it should be noted that it is labour intensive and currently there is no code of practice for the humane destruction of feral cats. Development of a code is identified as an action for this plan.
Historically, a number of trap types have been used to capture feral cats including steel-jawed traps and neck snares. These trapping methods are widely recognised as being inhumane and of little use in broadscale control programs. Soft-jawed traps, such as the Victor Soft Catch™ traps, are humane, are often used for the live capture of feral cats and represent a viable option for control. Soft catch traps have an adjustable pan that tensions the trap to prevent lighter non-target species from being caught.
Cage traps are also widely used, but are generally ineffective for trapping feral cats. Cage traps have, however, been effective in trapping stray and domestic cats around rubbish dumps and in nature reserves close to urban development (Edwards pers. comm.). To successfully trap feral cats, the lure or attractant chosen is most important. Research on a number of lure types is currently being undertaken (see below). Trapping as a control method is labour intensive and is only recommended where eradication is the objective, such as on islands or small areas.
Trained dogs have been used in the management of endangered species for tracking individual members of the species for capture and relocation (Best and Powlesland, 1985), as experimental predators to condition native captive-bred animals (J. Short pers. comm.) and to track, but not to ‘course’ or hunt, problem predators.
Indigenous Australians are able to offer unique skills in the management of natural areas, particularly in central and northern Australia where traditional skills are still taught and Aboriginal culture is less affected than in southern and eastern Australia. Aboriginal people are able to interpret the landscape and give insights into the natural history of certain species. In particular, some people are able to track individual animals. By employing such skilled people, problem predators can be tracked, resulting in the animals’ capture or destruction.
Tracking is a labour intensive technique but the time and expense may be offset by the benefit in being able to remove particular problem animals from the predator population. By selectively removing a few individual cats, such as large, experienced males specialising in hunting particular rare species, the primary agents of damage may be eliminated allowing wildlife colonies to survive even though there are other feral cats around (Gibson et. al. 1994).
Reviews of the history of pest management conclude that, in general, subsidies and bounties have rarely been effective in reducing damage by pest animals (Braysher 1993, Saunders et. al. 1995). As a general policy it is not cost-effective to seek to raise the level of recreational or professional hunting or trapping of feral cats on a broad scale by payment of bounties, subsidies or other similar artificial market incentives. Where private land adjoins or contains important wildlife habitat, assistance or encouragement to landowners and the development of incentives to promote feral cat control on private land may be appropriate, especially if the property forms part of a buffer zone to protect threatened species populations.
Baiting is usually the cheapest and most effective broadscale technique for controlling the numbers of inconspicuous small and medium-sized pest animals. Baiting techniques for feral cats currently appear much less effective than techniques for baiting dogs and foxes. This may reflect the fact that, until recently, little research had been conducted on control strategies for feral cats.
Baiting feral cats is difficult as they are often found in low densities, can have large home ranges, are disinclined to feed on carrion except during drought or during food shortages, and are naturally wary. A successful feral cat bait must be able to be detected by, and be attractive to, feral cats particularly where they occur at low densities. The timing of a baiting program is a critical element in the successful baiting of feral cats (Short et. al. 1997, D. Algar pers. comm.).
Applied Biotechnologies in an unpublished 1996 report to the New Zealand Department of Conservation, reported that a range of baits tested did not appear to be significantly more effective than commercial cat food as attractants. Shea (1996) announced the development by the Western Australian Department of Conservation and Land Management of a bait which is attractive to cats, but this bait has yet to be widely evaluated.
Development of an effective baiting technique, and the incorporation of a suitable toxin for feral cats, is a high priority as it is most likely to yield an operational and cost-effective method to reduce cat numbers in strategic areas.
The use of cyanide in Australia for pest control is currently illegal except under permit for research. Algar and Kinnear (1992) developed the use of cyanide as a research tool for studies of fox ecology. The technique has also been used to assess bait preferences of feral cats (Friend and Algar 1995; Algar and Sinagra 1996). The use of cyanide as a control technique was also evaluated by Marks and Gigliotti (1996) who found that there was some benefit in using it as a means of taking foxes to measure population parameters, develop indices of abundance, verify target/non-target impact and monitor rates of re-invasion. This was a consequence of the speed with which the poison acted and was seen as being humane. An ejector system to deliver the poison was also developed, but this remains a tool for research and has not been licensed for general use. The capacity to use this technique on feral cats has not been evaluated.
Development of a felid-specific toxin has been identified as a priority for feral cat control. The development of such a toxin must have due regard for humaneness, species specificity and a suite of other issues. An appropriate delivery system needs to be developed that is capable of minimising non-target exposure; meets the needs of agencies in applying the baiting system over chosen areas; and is cheap, safe and easy to deploy. Application of such a system will need to be complemented by an education and awareness program.
Preliminary studies by the Victorian Institute of Animal Science (Department of Natural Resources and Environment) have identified a possible felid-specific toxin. Trial results demonstrate that the toxin is effective and observations made by a veterinary surgeon on the clinical signs of the toxicosis suggest that the toxin is humane. With Commonwealth support, the Victorian Institute of Animal Science and the WA Wildlife Research Centre (Department of Conservation and Land Management), are undertaking complementary laboratory and field studies to investigate the feasibility of using this toxin. Future development of such a toxin will have due regard to the assessment of pain and the humaneness of the toxin in its application as a control technique.
Feral cats’ hunting skills rely on audio and visual stimuli rather than an acute sense of smell. Researchers within Australia are currently examining audio and visual attractants that will lure feral cats to baits. Bait additives that enhance smell and taste are also being evaluated. Certain lures being examined may also be used to trap cats and monitor cat abundance.
Feral cats and foxes are known to use rabbit warrens as dens or shelter. They are therefore vulnerable to techniques such as fumigation. Native wildlife such as goannas, other reptiles and small native mammals also use rabbit warrens and may be at risk of exposure to the fumigants. Any use of fumigants would have to take account of the risk to native species.
Aside from the risk to native species there are serious concerns about the animal welfare implications of using certain fumigants. Williams et. al. (1995) regard chloropicrin as inhumane. The risk to operators using fumigants such as chloropicrin is also recognised in terms of stringent handling requirements under occupational health and safety guidelines.
In 1977 the viral disease Feline panleucopenia, also known as feline parvovirus and feline enteritis, was introduced to sub-Antarctic Marion Island by South African wildlife authorities to control feral cats (van Rensburg et. al. 1987). The disease caused a significant reduction in the island's cat population, but feral cats were not eradicated until 1992 after a concerted effort combining trapping, baiting and shooting (Bester 1993). The reason for the initial success of biological control is that the cats had no immunity to the disease.
Feline panleucopenia occurs in feral cat populations on all large land masses including mainland Australia and Tasmania. This disease causes high mortality in non-immune populations, but confers immunity on survivors. Screening of blood samples in Australian feral cats indicates that there is widespread immunity to the disease (Moodie 1995). This suggests that the disease is already circulating through feral cat populations and any control effect is already operating. For mainland situations this disease has little tactical value and its deliberate introduction to susceptible populations may be questioned as inhumane (Copley 1991, Moodie 1995) as well as being of concern to the legitimate pet trade.
For Australia, it seems unlikely that there are any felid-specific pathogens that may be suitable as biological control agents, that is, any that are sufficiently virulent, humane and from which domestic cats can be protected (Moodie 1995).
Substantial efforts are being made at the Vertebrate Biocontrol Co-operative Research Centre to develop immunocontraceptive vaccines for several vertebrate pests, particularly foxes, rabbits and mice. This is a high cost/high risk venture and it would be inappropriate to expand the program to include work on cats at this time. If this venture is successful, it may be possible to apply the techniques to develop such a vaccine for feral cats. Currently there are no effective chemical sterilants which produce permanent sterility in cats (Moodie 1995).
A major benefit of the development of immunocontraceptive techniques is that they are humane. Broadscale control of cats using an immunocontraceptive vaccine, if one were developed, would be dependent upon the development of a suitable delivery mechanism for the vaccine and appropriate approvals to release the vaccine into the wild.
At present the most effective management technique for wildlife vulnerable to terrestrial predators, such as feral cats, relies on barriers. In many cases these are natural barriers–stretches of water surrounding islands–but a number of small reserves have been enclosed with predator-proof fencing (Coman and McCutchan, 1994, Aviss and Roberts, 1994).
Translocations of threatened species and eradication of introduced predators on islands have been important strategies for wildlife conservation (Burbidge 1989). Eradication of feral cats has been achieved on a number of Australian islands (Copley 1991, Burbidge 1989), in New Zealand (Veitch 1991, Burbidge 1989) and in the sub-Antarctic (Bester 1993). Where there are no suitable islands, fenced exclosures have been used to separate vulnerable species from introduced predators.
A review of predator-proof fencing in Australia (Coman and McCutchan 1994) has found that, although most fences are a significant barrier to foxes and feral cats, even the most elaborate can be breached. If breached, fences increase the vulnerability of endangered species by preventing their escape from the predator(s). To minimise this risk, fencing should be combined with an integrated baiting and trapping program to reduce the frequency of challenge to the fence by incoming predators. The combination of fencing with a baiting and trapping program is an expensive option which is likely to be useful only for small areas or areas with specific characteristics, such as peninsulas. It may also affect movements of other wildlife, preventing their dispersal and interbreeding with other populations. Recent projects in Shark Bay, WA, have sought to use a combination of conventional control methods, natural water barriers and fencing to create large predator-free reserves on peninsulas (Department of Conservation and Land Management 1994).
Although it is recognised that habitat fragmentation has the potential to deplete species richness (Bennett 1990) and to increase the incursions of invasive species, the magnitude of the impact of this invasion is not well quantified (May and Norton 1996). Observations have been made that feral predators such as foxes and dingoes use roads and other easements to travel through or gain access to areas where they hunt (Catling & Burt 1995 & 1997 Mahon et.al.1998) but that cats tend to move directly across roads or travel only short distances along roads (Edwards pers. comm.). This behavioural difference has direct implications for the study and control of cats. Weed incursions and human activities, such as tree removal, alter the floristics and complexity of the vegetation (Bennett 1990). Claridge et. al. (1991) suggested that as a consequence of social interactions, female and juvenile bandicoots were affected by logging activities and subsequent incursions by foxes and wild dogs. It has also been recognised that roads, in particular, affect small forest mammals, depending on the traffic volume, road surface, and activity and foraging patterns of the mammals (Oxley et. al. 1973).
Components of the environment may be manipulated or managed in order to reduce the damage done by feral cats. Therefore, habitat management in itself represents a critical factor in feral cat control. Native animals may be more secure in structurally complex habitats (Dickman 1996) so management of habitat to reduce fragmentation (rehabilitation of fire trails, roads and clearings) and to increase the density of vegetation (perhaps by better managing fire and grazing) may be effective in reducing the level of feral cat predation. This issue may need clarification to quantify the impacts of feral cats on native animals and make recommendations for future work in this area. In addition, the rabbit calicivirus disease (RCD) monitoring program may provide some answers on the response of predators to reduced rabbit densities.
Published June 1999 by Environment Australia under the Natural Heritage Trust.
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