How Many Animals Do Cats Really Kill?

New study shows: Cats kill many more animals than previously thought.

Posted Aug 09, 2020

One of the main reasons that humans domesticated cats is their ability to hunt and kill rodents like rats or mice in order to prevent them from eating human food supplies. While this is not the main reason to keep a cat as a companion for most people nowadays, free-roaming domestic cats will still hunt rodents, but also other prey animals like small birds or insects, and sometimes bring them home. 

A new study from South Africa now systematically investigated how often cats really kill prey animals when roaming outside the house—and the number is surprisingly high (Seymour et al., 2020).

The scientists first analyzed the data from three questionnaire surveys in which cat owners in Cape Town, South Africa, were asked about how much prey their pet cats returned home. In a second step, the scientists analyzed video footage from 25 of the cats that were included in the first step of the study. These cats were outfitted with animal-borne video cameras. In this way, the scientists were able to assess how many animals the cats actually killed and how many they returned home.

The results showed that there was a strong discrepancy between the number of animals that were killed by the cats and the number of animals they brought home. Overall, only 18 percent of the prey that the cats caught in the wild was brought home.  This suggests that on average, free-roaming cats kill about 5.5 times as many animals in the wild as they bring home. Most of the animals that the South African cats killed were reptiles (e.g, geckos or lizards), followed by mammals like mice (24.2 percent of kills), invertebrates like insects (21 percent of kills) and birds (1.6 percent of kills). These numbers are of course strongly dependent on the landscape cats are hunting in. In most of the U.S., reptiles will probably play a less significant role as prey for cats than in South Africa.

Based on the numbers of killed animals within the study period, the scientists calculated that the average free-roaming cat in Cape Town kills between 59 and 123 animals per year, with the average being 90 animals per year. As there are approximately 300,000 domestic cats in Cape Town, the scientists estimated that they kill the staggering number of 27.5 million animals per year. In towns with a larger population of free-roaming cats, this number would of course be even higher. Thus, free-roaming cats have a strong negative impact on the populations of the species they prey on. While this might be a good thing for some species that are considered pests (e.g. mice), it might also affect rare and endangered wildlife negatively.

What do the results of this study mean for cat owners? 

The scientists suggested that it is important to involve cat owners more strongly in conservation efforts for endangered species that get hunted by cats—for example, by implementing citizen science projects. Another suggestion was that cats should be kept indoors at night and allowed outdoors during the day since 92 percent of the kills happened at night. This way, the number of kills of endangered species could be drastically reduced, without permanently confining the cats to the house. Moreover, brightly colored cat collars could alert prey and reduce the number of kills. 

References

Colleen L. Seymour, Robert E. Simmons, Frances Morling, Sharon T. George, Koebraa Peters, M. Justin O’Riain. (2020). Caught on camera: The impacts of urban domestic cats on wild prey in an African city and neighbouring protected areas. Global Ecology and Conservation, 23, e01198.