A Diversity of Opinions: Trap, Neuter, & Release of Feral Cats

Sally Box, the Australian Threatened Species Commissioner, has her hands full. On Facebook, Box writes “Why isnt #TNR an ethical way of reducing #FeralCats?” and receives a barrage of support and disdain. Trap, neuter, and release (TNR) of feral cats (Felis catus) is not only contentious in Australia, but is controversial across the globe. The method generally involves cats being trapped, transported, desexed and then released back into an environment. The argument follows that eliminating a feral cat’s ability to reproduce will in time reduce or eliminate the populations. The controversy created by managing cat populations is unsurprising, considering the rich and dynamic human-cat relationship which pre-dates ancient Egypt and continues to this day. As a predator and introduced species, Felis catus has a complex impact on other species. Studies suggest that feral cats have played a role in the vulnerability and extinction of certain species. Also frequently discussed is the seemingly brutal and barbaric way in which feral cats hunt and kill their prey. These two reasons, the environmental and ethical, stir huge public support for TNR as a humane and effective way to reduce feral cat populations thereby maintaining biodiversity and reducing suffering to wildlife.


The environmental issues:

While varying opinions are common amongst laypeople, researchers generally have come to similar conclusions regarding the efficacy of deploying TNR to reduce cat populations. An Australian Parliamentary Research Inquiry documented studies which specifically examined mathematical modelling feral cat reproduction and field studies inquiring into feral cat  predatory behaviour.

The findings across a dozen or so studies suggested that TNR could only be effective when:

  • The feral cat population is small

  • There is accessible terrain for trapping

  • The area is closed from further from feral cat immigration (feral cats are territorial and therefore when cats are taken from the environment, other cats may move in from other areas and quickly reproduce if more food is available)

  • When sterilization is practiced on 74-94% of the population on an ongoing basis

  • Has ongoing funding and community support

Given these difficult prerequisites for TNR, the method appears impractical for many feral cat populations around the world. In Australia, for example, there is a population of  up to 18 millions feral cats across 3 million miles of land. If TNR can only be effective under such specific circumstances, are there any other effective methods to deal with feral cat populations? To the untrained eye, it seems trapping and euthanizing would be only slightly more effective in diminishing populations compared to TNR. Other methods, like shooting and baiting are more concerning from a welfare aspect, though are still constrained by possible feral cat immigration and accessibility. It seems that from when a feral cat population is large, has potential cat immigration and lives in inaccessible terrain, management programs will only have a slight effect, regardless of the method.

Another consideration for conservationists is how the reduction in a feral cat population will impact other species. Felis catus, as a species, has been welcomed within human environments for millenia for its role in reducing rodent populations. In relation to natural environments, Glen & Dickman (2004) acknowledge that managing Felis catus may have undesirable effects on other “pest” species and in turn to native wildlife. The authors suggest that the reduction or removal of a predator like Felis catus may release other species from predation or competition thereby resulting in trophic cascades. Using a simple example from Australia: a dramatic decline in feral cats will allow the “pest” rabbit population to grow. An increase in rabbits may put pressure on native plant sources, thereby straining the kangaroo population. Because of less predator competition from Felis catus, a native predator like a Quoll would increase in population and prey on smaller marsupials, which may happen to be endangered. The elimination and reduction of an introduced species could thereby unintendedly reduce biodiversity - something completely antithetical to the conservationist framework.


The ethical issues:

Whether TNR is a more humane method than other management techniques remains a difficult question to answer. Jessup (2004) firstly argues that releasing cats back into an environment is morally problematic because they will prey on native wildlife. While this account is totally factual, the researcher fails to recognize that wildlife experience similarly traumatic forms of suffering such as disease, starvation and physical injury that occur regardless of a feral cat’s presence in an environment. Coincidently, Jessup then attests that feral cats live in harsh conditions and thereby are better adopted or euthanased for their own wellbeing. Jessup, like the rest of the conservationist establishment, lacks one fundamental question from the discussion: How does the management of feral cats impact the welfare of other animals within the environment?


The welfare matrix:

When considering the environmental impacts of feral cats, the predators are often demonized by the way in which they stalk, hunt and kill their food. This is the most obvious welfare issue when considering the impact of feral cats in an environment. However, the presence of feral cats may have a welfare impact on non-prey animals as well. Due to the constrained carrying capacity in environments, many animals will die when they are young or experience suffering from disease and starvation. Food webs are complex interlinked systems, and any changes in populations can have far reaching effects. The absence or presence of feral cats could therefore be a critical consideration when attempting to understand the welfare of other animals.

Here’s a (very) theoretical example involving a (very) simplified environment containing populations of feral cats, rabbits, kangaroos and dingos in a bountiful grassland.


Background information:

Dingos are the apex predator in this environment. Dingos live to 7 or 8 years before succumbing to  disease, starvation or inter-species predation. Female dingos are expected to produce a litter of 5 pups annually, although some may perish if food is lacking or if they find disfavor with the alpha male or female.

Feral cats live up to 2 years before succumbing to predation (from dingos), starvation or disease. Female cats are expected to produce around 12 kittens annually, although around 50% are expected to perish in their first year.

Kangaroos live up to 6 years before succumbing to predation (from dingos), starvation or disease. Female kangaroos are expected to have 1 to 2 joeys annually, and many are expected to live to maturity.

Rabbits live up to 1 year before succumbing to predation from dingos or cats, or disease and starvation. Female rabbits produce approximately 25 young annually, although 80% are expected to perish before reaching 3 months.

Situation A: The feral cat population is reduced on the grassland:

- Dingos now have less predatory competition (from feral cats), and have more available prey. Populations are expected to increase.

- Rabbits would become more populous with their primary predator (feral cats) not present. Populations are expected to increase.

- Kangaroos would reduce in population, as they now compete for food with the growing rabbit population. The increase in dingos would also put pressure on Kangaroo populations. Populations are expected to decrease.

Situation B: The feral cat population grows on the grassland:

- Dingos now have more predatory competition (from feral cats), thereby decreasing dingo populations.

- Rabbits would become less populous with their primary predator (feral cats) now growing in number. Populations are expected to decrease.

- Kangaroos would increase in population, as their main competitor (rabbits) is now decreasing in population. Populations are expected to increase.

The welfare matrix:

As the example shows, the presence of just one species can substantially alter an environment. When considering the individuals rather than species in an environment, it can make a world of difference. From a species perspective, both situations are the same: each has 4 species present. However, from a welfare perspective, Situation A would have a far higher population, as the rabbit population booms from their swift ability to reproduce. Why does that matter? Is it better to have environments with more individuals? It’s difficult to say without a clear understanding of the welfare of the animals within each species.

From the outset, it seems that the high mortality rate of rabbits is a key welfare consideration. Also, because the rabbit is the main prey species, the welfare outcome looks less favourable. Would that swing the welfare dial toward Situation B, as fewer rabbits are present? However, starvation and disease are also common forms of death in natural environments and could produce just as much or even more suffering than being eaten alive. This brings feral cats, dingos and kangaroos into the equation. Without understanding what life is like for these animals, it’s difficult to come to any clear conclusions. What’s clear is that the altering of feral cat populations or any species (introduced or otherwise) will change the population size and wellbeing of animals present in the environment. That is something that is necessary to consider, if we are to properly understand the ethical grounds to manage animal populations or implement programs like TNR.

For species diversity, TNR (or any feral cat management method) appears only effective in specific situations. For the welfare of the individual cat, TNR seems to produce better outcomes than being baited, shot or left in the wild without vaccination. For the welfare of all the individuals within an environment, the impact of TNR is currently unknown. This third proposition makes the feral cat issue even more complex. However, situations that are difficult should not be considered unimportant. Nonetheless, Sally Box and the Australian Government has taken a step backwards, declaring a ‘War on Cats,’ with the intention of trapping, poisoning and killing some 2 million felines by 2020. There is much skepticism as to how this program will produce any positive biodiversity outcomes in the long term. On this occasion, the welfare issue has not even been given lip service. There remains the need to publicly push for the consideration of the welfare of feral cats, and the need for research and an honest dialogue into the wellbeing of wild animals beyond just biodiversity.









Oliver Hornung