The Effect of Feral Cats on Urban Wildlife

When people consider the causes of the decline in bird or small mammal populations most will first think of pesticides or vehicle deaths. However, one of the biggest threats to these birds and mammals may actually be our own dear pet cats.

Domestic cats (Felis catus) contribute significantly to the decline in urban wildlife. Cats kill a large number of birds, small mammals and reptiles every year. In the United States alone, Loss et al. (2013) estimated that they kill between 1.3 and 4.0 billion birds and between 6.3 and 22.3 billion mammals per year. Most of these deaths are caused by un-owned, feral cats. A study in New Zealand found that cats there killed enough urban birds to significantly impact their populations. The presence of cats can also increase the stress and fear experienced by their prey. Fardell et al. (2023) found that free roaming cats in urban environment created a “landscape of fear” with reduced wildlife activity and reproduction. All in all, urban wildlife populations are significantly negatively affected by cats, especially feral ones.

Currently, one of the most popular ways to combat the feral cat problem is the trap-neuter-return method. This method is popular with the public, who see it as an animal friendly way of dealing with the problems caused by feral cats. For this method they capture the feral cats and neuter them. Then they check if the cat can be socialized and adopted by humans. If this is not possible, they release them back. A piece of the cat’s ear is removed to keep track of which cats have already been neutered. Since the cats can no longer reproduce after being neutered the assumption is that the feral cat population will get smaller over time, thus reducing their negative effect on the wildlife (Hostetler et al., 2020).

However, the actual effectiveness of the trap-neuter-return method is debatable. There are two factors that reduce the effectiveness of the method. Firstly, the feral cat colonies are not closed populations. Stray cats from other areas are attracted towards the colonies and people keep illegally abandoning their pets, increasing the colony sizes. Secondly, it is very difficult to capture all cats in an area. This means that some cats will not be neutered and are thus still able to reproduce (Hostetler et al., 2020). It is estimated that between 71% and 94% of the cats need to be neutered for the population to decline. In practice, trap-neuter-return programs often capture less than that, meaning feral cat population remain stable or even increase (Foley et al., 2005).

In summary, trap-neuter-return programs in their current form are an ineffective way of reducing populations of feral cats and their negative effects on wildlife abundance. To effectively reduce the feral cat populations, it is important to prevent new stray cats joining them or else their numbers will never go down (Lohr et al., 2013). This can be done by, for example, sterilizing pet cats and keeping them indoors (Hostetler et al., 2020). That way the feral cat populations will actually go down and their negative effect on wildlife populations will be reduced.

For previous posts on urban cats, check out:

– Domestic cats in Urban Environments: Should an Invasive Apex Predator be allowed to stay on the hunt?
– Cats versus rats in the city; a surprising winner
– Cat colonies and flight initiation distances of urban birds: Dealing with conflicting sources of citizen wellbeing

References

Fardell, L. L., Pavey, C. R., & Dickman, C. R. (2023). Influences of roaming domestic cats on wildlife activity in patchy urban environments. Frontiers in Ecology and Evolution, 11. https://doi.org/10.3389/fevo.2023.1123355

Foley, P., Foley, J. E., Levy, J. K., & Paik, T. (2005). Analysis of the impact of trap-neuter-return programs on populations of feral cats. Journal of the American Veterinary Medical Association, 227(11), 1775–1781. https://doi.org/10.2460/javma.2005.227.1775

Hostetler, M., Wisely, S. M., Johnson, S., Pienaar, E., & Main, M. (2020). How Effective and Humane is Trap-Neuter-Release (TNR) for Feral Cats? EDIS, 2020(2), 8. https://doi.org/10.32473/edis-uw468-2020

Lohr, C. A., Cox, L. J., & Lepczyk, C. A. (2013). Costs and Benefits of Trap‐Neuter‐Release and Euthanasia for Removal of Urban Cats in Oahu, Hawaii. Conservation Biology, 27(1), 64–73. https://doi.org/10.1111/j.1523-1739.2012.01935.x

Loss, S. R., Will, T., & Marra, P. P. (2013). The impact of free-ranging domestic cats on wildlife of the United States. Nature Communications, 4(1), 1396. https://doi.org/10.1038/ncomms2380