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Killers in Your Garden

Timothy Boyer Ph.D.'s picture
Cats kill more wildlife than previously believed.

A new study reveals that house cats allowed to roam free, actually kill more wildlife in your neighborhood than other similarly compared wild predator species. Here’s the facts about the study and how this could affect your garden.


Earlier, we discussed how that Bluebirds in your backyard are an effective means of natural pest control in your yard and garden. But what do you do when another common backyard pest—such as your neighbor’s cat—is killing the birds in your yard?

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While this may seem to be a rather small problem—after all, cats being cats are only doing what comes natural, so what’s a few birds? According to a new study, it’s much more than a few birds; house cats running free actually have a large and detrimental effect on local wildlife.

According to North Carolina State University News, a new study was recently published as a collaboration of researchers from NC State University and the North Carolina Museum of Natural Sciences along with citizen scientists from six countries to collect GPS cat-tracking data and prey-capture reports from approximately 925 cats to determine just how much wildlife is killed off by roaming non-feral house cats.

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Although house cats are typically kept fed on a diet of pet food it’s generally assumed that the occasional bird captured outside makes up only a very small part of their diet in comparison to other predators living in the wild. However, as it turns out, in a scientific comparison it’s a numbers game when you factor in the number of kills within a specific range—call it a kill zone density if you will.

With assistance from citizen scientists, inexpensive GPS tracking devices were placed on the cats’ collars so that pet owners could participate in tracking where their cats went and report on the number of prey they brought home. The data gathered was statistically extrapolated to account for an unobserved expected prey count and then divided by the area in which each cat was electronically tracked.The cats were found to roam within approximately 100 meters of their homes.

After number crunching the data, what the researchers found was that the house cats killed an average of 3.5 prey/month, leading to an estimated ecological impact per cat of 14.2‐38.9 prey per hectare per year. A hectare is the area covering a square with sides of 100 meters by 100 meters.

“Since they are fed cat food, pets kill fewer prey per day than wild predators, but their home ranges were so small that this effect on local prey ends up getting really concentrated,” said Roland Kays, the paper’s lead author. “Add to this the unnaturally high density of pet cats in some areas, and the risk to bird and small mammal population gets even worse.

“We found that house cats have a two- to 10-time larger impact on wildlife than wild predators—a striking effect,” he added.

Here is a YouTube Video About the Experiment and its Findings

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The Effect Stray Cats Can Have On Your Garden

There’s more to consider than beneficial birds being killed in your yard. Cats will also kill small reptiles such as lizards, which are credited with contributing to insect pest reduction. Furthermore, cats at times like to chew on plants such as zinnias, marigolds, rosemary and bean sprouts. And, the soft garden dirt makes a tempting sand box after a meal.

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How to Keep Stray Cats Away

While there’s nothing like a dog to keep cats away, they do not provide 24/7 protection. However, there are a number of practices that can keep stray cats away:

Remove Attractants—Food and shelter attracts cats. Therefore, you should avoid feeding cats or setting out food for other wild animals on your property under the porch or a protected doorway. In addition, remove trash and secure garbage bins where cats typically scrounge around looking for scraps. Clean up any leftover food, drinks or pet food left outside the house, which will also keep rodents away that may cause cats to zero on your property as a potential food source.

Invest in Chemical Cat Repellants—Try a variety of liquid and granular cat repellants such as those that contain pepper-based ingredients that irritates a cat's sense of smell and taste. Some repellants mimic other animal species urine that could discourage a cat from entering your area.

Try Mechanical Repellants— Installing a motion-activated sprinkler is enough to annoy most cats. You may have to reposition it periodically, but a stray cat should eventually associate the annoyance with your yard and learn to stay away.

If you have a favorite method for keeping stray cats away, please share what works for you in the comments section below.

Timothy Boyer has a Ph.D. in Molecular and Cellular Biology from the University of Arizona. For 20+ years he has been employed as a freelance health and science writer. Today, with a background in farming and an avid home gardener, Timothy continues writing about science with a focus on the connection between plant biology and gardening for healthy living. For continual updates about plants and health, you can also follow Timothy on Twitter at TimBoyerWrites.


Keeping Cats Indoors Could Blunt Adverse Effects to Wildlife” by Mic Kulikowski for North Carolina State University News, March 2020.

The small home ranges and large local ecological impacts of pet cats” Roland Kays et al.; Animal Conservation, First published: 11 March 2020.