Outdoor cats are a contentious issue for cat-owners, cat-lovers, and those that are concerned about the environment. Like it or not, Fluffy is doing a LOT of damage (Image credit: Cat Outside in Sweden-148884.jpg by Jonatan Svensson Glad, CC BY-SA 4.0, Image Cropped).

I hate to be the bearer of bad news, but domestic cats are bad for the environment. Sure, we as a species have adopted and incorporated them into our society (I live with two, myself), but that doesn’t mean we aren’t responsible for them and their actions.

The other week I saw a tweet from a cat owner saying that their domestic outdoor cats weren’t a problem for native birds and other wildlife, but feral cats and pesticides were the true killers. Thankfully Dr. Holly Jones (@DocHPJones) responded to the tweet with some hard facts and scientific evidence for why domestic cats are an issue, and just how much damage they can really do. Not surprisingly, her tweet was met with lots of resistance from cat owners and cat lovers alike, stating that it’s “natural to let them hunt” and “they aren’t that big of a problem”. The unfortunate thing its that, like it or not, cats ARE that big of a problem.

This is wrong. Outdoor house cats kill birds (and lizards and snakes and frogs and toads and bugs and chipmunks and squirrels). Keep your cats inside or on a leash if you like birds and other wildlife. That’s it. That’s the tweet. https://t.co/N34FKLcDLy — Holly Jones (@DocHPJones) September 20, 2019

Cats and the Environment

We’re all familiar with cats, and those of you that own/know people that own them know that there are two kinds, indoor cats and outdoor cats. Indoor cats are exactly what they sound like, pampered fluffballs that lounge around the house, waiting for their servants (humans) to feed them again (if I had a nickel for every time my cat begged for food I’d be a VERY wealthy man). Outdoor cats, on the other hand, are where things get problematic. These cats are responsible for the deaths of BILLIONS of birds and other wildlife the world over.

One of the big issues is that cats occur in very high densities as a result of their roles as pets for humans. Because we feed them and take them with us, these cats occur at higher densities than predators normally could in nature, as they are not reliant on a local prey population to sustain them. Consequently, native wildlife is vulnerable to many more predators than they normally would be. For example, a given habitat may normally support a small population of top predators, let’s say two or three cats. But, because they are fed by their humans and no longer have to compete with other cats, that same habitat is now “supporting” 20+ cats, which makes a huge difference for the local animals. Then, instead of a prey population being managed by a normal amount of top predators, the prey are completely wiped out by the larger than normal predator population.

Cats are obligate carnivores, and as such they have to eat meat. We feed them of course, so you may think that might prevent them from killing quite as much wildlife, but the thing about cats is that they are also notorious for killing animals and not eating them. If you own/have owned a cat, you have more than likely received an “offering” from your cat at one time or another. These spurious killings seem to be the cats way of showing off how good of a hunter they are, or perhaps ways to keep their skills sharp. Whatever it is, these offerings translate to additional (and unnecessary) mortality of local wildlife. Cat owners may use these offerings to estimate how many animals their cat kills, but they are not a good way to estimate the damage a cat does, as cats don’t always bring these kills home. In a study of farms in Poland, researchers estimated that, across all of the farms in the country, cats killed and brought home an average of 48 million mammals and 9 million birds per year, but killed (and didn’t bring home) an additional 583 million mammals and 137 million birds.

In one very extreme example, Lyall’s wren (Traversia lyalli) was once found throughout New Zealand, but its range was eventually restricted to Stephens Island in Cooks Strait. The common (and incorrect) story is that the species hunted to extinction by a single cat, the lighthouse keeper’s cat Tibbles. Tibbles certainly did plenty of damage himself, but other cats, feral or otherwise, helped him and contributed to the extinction of this bird.

Cat Owners and Their Responsibilities

By letting your cat roam free, you are contributing to the destruction of local environments and the native community of wildlife. I know it sounds harsh, and the cat lovers will be up in arms (not MY cat, surely. I only let them out every now and then….). It doesn’t matter. Cats are not only detrimental and destructive, this study has shown that cat owners themselves are part of the problem. By being either willfully ignorant of the actions of their feline companions or resistant to any action to limit their impact outside of neutering them (or some combination of both), cat owners that allow their pets outside are contributing to the problems that cats pose.

Additionally, it is the responsibility of cat owners to take heed of peer-reviewed scientific evidence. Misinformation is when people put forward information that goes directly against an overwhelming scientific consensus (look no further than climate change deniers and anti-vaxxers), but this is also an issue with cats. Cat advocates are known to spread misinformation about the damage that cats can do, and will actually seek to discredit the scientific evidence on the impact that cats have. For more information read this paper from Biological Invasions covering the events.

Take Home Message

Cats are bad for local wildlife. Period. If you own a cat, it is your responsibility to not only take care of them (and love them, of course), but to think of their impact on the environment and what you can do to limit that.

Also, indoor cats are healthier! They live longer, are less likely to be eaten by a predator themselves, they won’t get hit by a car, and they aren’t exposed to parasites. By keeping your feline friends indoors, you will give them AND the local wildlife better lives.

And An Added Bonus…

If you’ve stuck around for this long and would like to hear more about the lives of outdoor cats, consider tuning in to the latest episode of the podcast that my fellow EcoMass editor Sam Perrin and I run, Cinematica Animalia. It deals with last year’s “hit musical” Cats, and some of the facets of outdoor cat biology that are on display during the “film”.

Cinematica Animalia · S3E12- Cat-Ass-Trophe (Cats)

Adam Hasik is an evolutionary ecologist interested in the ecological and evolutionary dynamics of host-parasite interactions. You can read more about his research and his work for Ecology for the Masses here, see his personal website here, or follow him on Twitter here.