The phenomenon of outdoor cats preying on birds and mammals has a wide range of implications for the animal welfare landscape more broadly.

Outdoor cats preying on birds and mammals is a phenomenon that has caused a great deal of concern within the animal welfare community for some time. While prior research may have over-estimated the number of kills per year in North America, the fact remains that predation by outdoor cats is a significant cause of death for birds and mammals. In fact, more recent estimation methods indicate that outdoor cats kill 640 million birds and mammals in the U.S. and Canada combined.

Prior to the current study, it was previously hypothesized that the single most cost-effective means for curbing these kill rates is to permanently confine cats to remain indoors. For example, prior data simulations indicate that for every $1,000 spent on advocacy measures to convince guardians to confine their cats indoors, approximately 33 cats are actually confined (as a result of the advocacy) leading to a reduction of approximately 830 animals being killed. However, these simulations did not account for the relative importance of the varying components being simulated (e.g., the estimated number of cats with guardians, the estimated number of homed cats that are outdoor cats, the estimated number of cats predating on animals, etc.).

When modeling these results using more rigorous methods, the results indicate that at scale, a 10% decrease in the percentage of outdoor cats is associated with a decrease in kills of approximately 10 million birds and 43 million mammals. The most significant factor in this model was the assumed predation rate. Therefore, advocacy campaigns focusing on guardians using collars with predation deterrents (e.g., bright colors, bells) could result in a lower death rate than campaign efforts focusing on cat confinement. The assumed implication here is that people are more likely to comply with a request to use collars than they are to confine their outdoor cats to the indoors.

While these numbers show significant promise for reducing kills with advocacy measures, more information needs to be considered before action is taken. Specifically, we need to evaluate and consider the trade-offs associated with various advocacy campaigns. One factor to consider is the welfare of the cat. While veterinary associations recommend that cats are confined to the indoors, indoor confinement can lead to both mental and physical health issues as a result of boredom, inactivity, or stress. For example, indoor cats have a higher prevalence of diabetes, dental disease, urinary tract disease, and other ailments when compared to outdoor cats. Conversely, outdoor cats are more likely to become infected with pathogens or parasites and engage in risky behaviors that can lead to death (e.g., street crossing). Unfortunately, the overall impact on the welfare of the cat when confined is uncertain. There is no clear evidence that suggests confining cats to the indoors is optimal or vice versa.

Another factor to consider is the impact that cats preying on animals has on animal welfare at large. Since cats are opportunistic predators, they tend to target prey who are vulnerable such as sick, injured, or suffering animals. These targeting methods indicate that cats are likely to kill animals who are already dying and could expedite the suffering process. With that being said, cats are also more likely to target juvenile animals too, which could negatively impact the survival of those species.

Finally, cats prey on animals who have short lifespans and substantial reproductive capacity such as rodents, which suggests that preying on these animals has an overall positive impact on the welfare of such animals when considering competition for food, the likelihood of being poisoned or killed in traps, or the likelihood of surviving a harsh winter (only 5% are estimated to survive).

Overall, the evidence is somewhat open for interpretation, given the uncertainty in estimates (e.g., the scale of the problem), and the subjectivity around the concept of animal welfare. With that being said, the results of this study suggest that advocacy measures aimed at cat confinement are not likely the most cost-effective approach, and there may be some net positive benefits of outdoor cats preying on birds and mammals.