Population Control Options for Stray and Feral Cats

The aim of any cat population control program should be to prioritise the welfare of cats; reduce the impact of cats on native wildlife; and minimise cats’ disturbance to human populations; minimise the risk to non-target species, and be effective in the long-term. There is as yet no scientific consensus on the most humane and effective form of population control for stray and feral cats in urban and rural environments. Long-term success however does rely on strong public education in order to minimise the numbers of new animals entering un-owned cat colonies.

Being an introduced species, cats do not fill any existing environmental niche,[1] although they do serve some benefit in managing populations of other non-native animals such as introduced species of mice and rats. Cats have become such a problem because they are so good at breeding: they are induced ovulators; are able to reach sexual maturity by 4 months of age; wean kittens as young as 50 days old; and produce multiple litters of up to 6 kittens per year,[2] allowing them to rapidly fill niches. Cat populations also remain relatively stable by means of migration and natural attrition, with mortality rates of over 50 percent common for free-roaming kittens.[3], [4]

Cats are on the list of the 100 worst invasive species globally. They pose risks to their environment by endangering native wildlife;[5] impacting public health through the transmission of diseases such as parasites, and injury; and can themselves suffer severe welfare issues through parasite burden, fighting and injury, and infectious disease.

Cats live in various states of domestication: fully domesticated and living as pets; feral in a completely ‘wild’ state and unsocialised to people; or as strays, in a semi-domesticated state, having been abandoned by their owners. These populations can feed into each other, but their management generally requires different strategies. Current forms of population control include: poisoning animals in situ; trapping, removing and humanely euthanasing animals; or trapping, removing, neutering, and returning animals, or where possible, re-homing them.

Trap-Neuter-Release (TNR) programs have been a popular method of population control over the past few decades. The goal of these programs is to reduce population sizes and per capita growth rates within defined populations. Cats are trapped, neutered, and then returned to their original environment, thus reducing the population’s breeding potential. To be effective, programs require long-term colony management such as vaccinations and parasite control, limitations to public feeding, euthanasia of sick animals, rehoming, and control of immigration.[6] It is important that both male and females are desexed: neutering only some males would simply allow all the remaining males to mate more frequently, and speying only some females increase fighting amongst males and harassment of neutered females, leading to increased animal welfare risks.

 

There have been some success stories with this form of population control: one study reported an average decrease of cats in desexed colonies of 36% over 2 years, compared with an average increase of 47% in the 3 control colonies.[7] Another study reported a reduction of 26% in cat numbers after implementation of a TNR program in 132 colonies over three years.[8]

 

At this stage, however, there appear to be more problems than benefits to TNR programs. For population sizes to decrease permanently, the per capita rate of increase needs to be less than zero, and at least 70 percent of a colony must be desexed.[9] Because the only means of population reduction in TNR programs is via adoption or natural mortality, and migrating cats normally replace these losses, TNR programs are often inefficient in reducing population numbers.[10]

 

For TNR programs to be successful, there needs to be closed population pools, as defined by geographical location and a central feeding source. This is generally unfeasible for Australian rural environments due to the distances involved; lack of resources to conduct TNR programs and to ensure long-term management; and the adverse impacts of maintaining a cat population in areas of ecological importance. Most cat populations are too transient[11], [12] and are not sufficiently territorial to prevent unneutered animals from joining the colony, and thus counteract the natural attrition of neutered animals.[13] One study of 17 TNR programs found that 70 percent of cats remained in the colonies 5 years after the program commenced, and the fate of the other 30 percent of cats was unknown.[14] This can often be mitigated through adoption programs[15] and by only carrying out programs in urban or peri-urban areas, where there are well-contained areas and limited impact on local wildlife.

 

Aside from their lack of feasibility in many locations, TNR programs can both create and maintain animal welfare problems. The re-introduction of non-native animals may also conflict with local legislation and poses the risk of predation on native fauna. While there may be some enhanced welfare benefits to the cats themselves because of the reduction in mating-related fighting, unowned cats can continue to suffer poor health, being exposed to parasites and infectious diseases such as Feline Leukemia Virus, Feline Immunodeficiency Virus, Feline Infectious Peritonitis and Feline Enteritis. Feral cats have a lifespan 5 times shorter than owned cats and mortality rates can be as high as 80%.[16], [17]

 

Another significant issue is that the cost of running TNR programs is also greater than other control methods.

 

Other existing alternatives include cat free buffer zones, and fencing. Sentient strongly opposes the use of poison as a method of population control as it is inhumane, leading to a slow and painful death, and poses risks to non-target species. Effective, alternative methods to TNR appear to require long-term, coordinated efforts between veterinarians, animal welfare organisations, and the community, supported by robust legislation. Given that most new cats arriving into stray cat colonies are abandoned pets, priority should be given to educating the public about responsible pet ownership; legislating for permanent identification of all cats using microchips coupled with compulsory cat registration and trace-back; compulsory desexing of all non-breeding cats prior to puberty to prevent unwanted litters and roaming; the licensing of all cat breeders; and encouragement of indoor-only environments  and outside cat enclosures or escape-proof fencing.

 

For more remote areas, the solution is more ambiguous and Sentient supports further research into the development of innovative, effective and humane methods of control and eradication of feral cat populations. As most TNR research has been conducted in the United States, there is also a need for more localized trials in order to determine their efficacy.

 

 

 

 

[1] Longcore, T., Rich, C. & Sullivan, L.M. (2009) Critical Assessment of Claims Regarding Management of Feral Cats by Trap-Neuter-Return Conservation Biology, 23(4):887-894

 

[2] Scott KC, Levy JK, Crawford PC. Characteristics of free- roaming cats evaluated in a trap-neuter-return program. J Am Vet Med Assoc 2002;221:1136–1138

 

[3] Natoli E. Spacing pattern in a colony of urban stray cats (Felis catus L) in the historic centre of Rome. Appl Anim Behav Sci 1985;14:289–304

 

[4] Yamane A, Emoto J, Ota N. Factors affecting feeding order and social tolerance to kittens in the group-living feral cat (Felis catus). Appl Anim Behav Sci 1997;52:119–127

 

[5] Gibson et al., 1994; Christensen and Burrows, 1995, Friend and Thomas, 1995

 

[6] Analysis of the impact of trap-neuter-return programs on populations of feral cats; Castillo D. Population estimates and behavioral analyses of managed cat (Felis catus) colonies located in Miami-Dade County, Florida, parks. MS thesis, Department of Environmental Studies, Florida International University, Miami, Fla, 2001

 

[7] Stoskopf, M.K. and Nutter, F.B. (2004). Analyzing approaches to feral cat management – one size does not fit all. Journal of American Veterinary Medicine Association 225: 1361- 1364)

 

[8] Centonze, L.A. and Levy, J.K. (2002). Characteristics of free- roaming cats and their caretakers. Journal of American Veterinary Medicine Association 220: 1627-1633)

 

[9] Longcore, T., Rich, C. & Sullivan, L.M. (2009) Critical Assessment of Claims Regarding Management of Feral Cats by Trap-Neuter-Return Conservation Biology, 23(4):887-894).

 

[10] Castillo, D. and Clarke, A.L. (2003). Trap/Neuter/Release methods ineffective in controlling domestic cat “colonies” in public lands. Natural Areas Journal 23: 247-253

 

[11] Analysis of the impact of trap-neuter-return programs on populations of feral cats; Castillo D. Population estimates and behavioral analyses of managed cat (Felis catus) colonies located in Miami-Dade County, Florida, parks. MS thesis, Department of Environmental Studies, Florida International University, Miami, Fla, 2001

 

[12] Zaunbrecher, K.I. and Smith, R.E. (1993). Neutering of feral cats as an alternative to eradication programs. Journal of American Veterinary Medicine Association 203: 449-452

 

[13] Centonze, L.A. and Levy, J.K. (2002). Characteristics of free- roaming cats and their caretakers. Journal of American Veterinary Medicine Association 220: 1627-1633

 

[14] Feral cats in the United Kingdom. Journal of the American Veterinary Medicine Association 208: 520- 523.)

 

[15] Levy, J.K. and Crawford, P.C. (2004). Humane strategies for controlling feral cat populations. Journal of American Veterinary Medicine Association 225: 1354-1360

 

[16] Jessup, D.A. (2004). The welfare of feral cats and wildlife. Journal of American Veterinary Medicine Association 225: 1377-1383

 

[17] Nutter, F.B., Levine, J.F. and Stoskopf, M.K. (2004a). Reproductive capacity of free-roaming domestic cats and kitten survival rate. Journal of American Veterinary Medicine Association 225: 1399- 1402