Polish Farm Cats’ Impact On Local Wildlife
Studies have shown that house cats who are let outdoors, as well as feral and wild cats, can drive down wildlife populations. Cats kill almost 15 billion animals each year in the U.S. alone. In this study, researchers looked at the number of animals killed by cats on Polish farms. To estimate total deaths, they needed to know roughly how many cats there are, what kind of cats they are (e.g. mousers or housecats), and how many animals they kill.
Of 311 Polish farms surveyed, just over half (160) had no cats, and roughly a tenth (30) had three or more cats. This yielded an average of 0.83 cats per farm. Almost 80% of these cats were fed leftovers rather than cat food. A diet of leftovers suggests that most of the cats were mousers, kept primarily for their usefulness. That many are mousers has implications for potential interventions, as it means educational campaigns encouraging owners to neuter cats or keep them inside to protect wildlife are less likely to work.
To determine how many animals the average Polish farm cat kills, researchers tracked how many animals the cats brought home, and how many animals they ate. The guardians of 34 cats helped them collect data on the number of animals brought home each month. Looking at animal remains in cats’ scat and stomachs told the researchers how many animals they had eaten in the past day. They collected scat on and around the farms, and examined the stomach contents of cats shot legally by hunters or killed by cars along local roads.
Results suggested that cats brought home an average of 19 animals per year, but they ate as many as 246. The researchers acknowledged that some animal remains may have been scavenged rather than hunted, and so the number eaten may be somewhat higher than the number killed. Even so, cats likely ate around 10 times as many animals as they brought home.
Combining this data on average kills per cat with the number of cats per farm and the total number of Polish farms leads to an estimate of a vast number of animals killed every year. The study suggests that, in 2002-2005, cats on Polish farms brought home almost 50 million mammals and 9 million birds. They may eat as many as 583 million mammals and almost 136 million birds. However, it should be noted that the number of farms in Poland has plummeted since 2002 (in 2010, there were 30% fewer farms than in 2002). Since the paper was published fourteen years after the study was performed, there probably should have been a correction to the predation estimate given the declining number of farms in Poland. The authors state that they extrapolated the total number of cats on farms by multiplying the average number of cats per farm by 2.9 million, the number of farmsteads they reported to be in Poland in 2002. Today, the actual farm cat population might be 50% of the number estimated by the paper and total cat predation would consequently also be 50% lower than estimated.*
Cats are hugely popular as companion animals, and many are allowed to roam as outdoor cats. While the exact impact of outdoor cats is debated scientifically, most animal advocates know that our love of cats is yet another human pressure on wildlife. If we want to protect local wildlife, we can shift towards keeping cats indoors, support TNR programs whenever possible, and ensure that our cats are well-fed to reduce their need to hunt.
*For further analysis and critique of this study’s methods, see commentary below by Peter J. Wolf.