Geoff CarpentierWhat a lovely sight! Look at Patches as she heads out for her morning jaunt in the fields near her home. How cute is she as she tiptoes through the dew-drenched grass, trying her best to keep her paws dry?

Millions of cats do exactly this every day, and the outcome is always devastating for billions of wild animals and sometimes for the cat as well.

Each year about five percent of Canadian birds are killed by cats – 269 million birds out of an estimated population of 10 billion, to be exact.

Free-roaming cats live an average of five years, compared to 17 years for indoor cats. During those five years, they can do irreparable damage to local wildlife.

Plus, many predators out there would happily snap up an unwary cat for dinner. Coyotes, in particular, seem to hunt cats in urban areas since cats are plentiful and generally less wary than most wild prey.

Why would you let your cat kill other animals?

But what of the animals your sweet little kitten hunts?

Surprisingly, I have several friends who are devout naturalists but willingly let their cats out, knowing the harm they do. This always puzzles me: If you cherish wildlife, why would you let your cat roam and kill wild things unnecessarily?

There are two distinct camps when it comes to this issue:

  • those who let their cats out because “cats need to roam and exercise their hunting instincts;.”
  • those who know it’s harmful and wrong and want to protect wildlife.

Around the world, this debate rages and has done so for many decades.

In 1916, in his report to the Canadian Commission of Conservation, W.E. Saunders of the McIlwraith Ornithological Club of London, Ont., and a pioneer on bird studies, wrote:

“The cat, I think, comes fairly under the jurisdiction of the Conservation Commission. I wish it would appoint me Cat Ranger. If that were done, I can assure you the number of cats would suffer a very serious diminution every year because, as you know, every cat spends most of its time in an effort to kill. It kills not only the mice but every bird it can possibly catch and, as I look at it, each insectivorous bird killed by a cat is worth more than the cat itself. I have proved that there are some uses for cats. Buried under apple trees I have eaten them as apples; buried under rose bushes I have picked them in the form of roses. That is a very satisfactory way of disposing of cats.”

Many studies have been undertaken worldwide recently trying to determine the impact the estimated 600 million cats have on wildlife. This number includes feral (i.e. born in the wild), escaped or released and now living wild, and those cats kept as pets but permitted to be free-roaming.

Domestic cats are a threat to biodiversity

Domestic cats are recognized as a threat to global biodiversity and are known to have significantly contributed to the extinction of 33 species worldwide. The impacts are so great that the International Union for Conservation of Nature (IUCN) lists domestic cats as one of the world’s worst non-native invasive species.

Outside North America, the number of kills is immense. According to the Royal Society for the Protection of Birds, 27 million birds are killed annually in Great Britain by the 7.2 million cats residents keep as pets. Another study, conducted by Michael Woods, Robbie A. McDonald and Stephen Harris, estimates that the impacts in Great Britain may be as high as 150 million birds.

In Switzerland, it’s estimated that 100,000 to 300,000 birds are killed annually by cats.

In Australia, the problem is equally severe and based on the estimated 14.6 million cats (free-roaming and feral) found there, numbers are again staggering. The 2.6 million free-roaming Australian pet cats alone take an estimated 3.8 million animals annually, with about 25 percent of those being birds.

Add the superior hunting feral cats to the mix (estimated to be up to three times as efficient as free-roaming cats) and the numbers likely approach 41 to 54 million animals, including about 10 to 13 million birds.

In 1996, C.R. Dickman presented a report to the Australian Nature Conservation Agency and the Institute of Wildlife Research in Sydney, Australia, regarding the Stephens Island wren. This flightless, nocturnal wren from New Zealand went extinct about 1900. It was never observed alive in the wild. Sadly, most of the known museum specimens were collected by a single cat.

An unscientific New Zealand study reported that an estimated 1.4 million free-roaming cats kill 19 million animals annually, including approximately 1.1 million birds.

In North America, recent studies concerning the impact of the estimated 30 to 80 million feral and 33.6 to 58.8 million free-roaming cats support these figures. Studies by various scientists estimate the average kill rate for each free-roaming cat in the United States to be between four and 54 birds a year, depending on location and degree of urbanization.

A landmark article by Scott Loss, Tom Will and Peter Marra, in Nature Communications (2013) details the problem. “The Impact of free-ranging domestic cats on wildlife in the United States” created a media frenzy as hundreds of articles ensued summarizing and critiquing their data. In their paper, the authors state in part:

“We estimate that free-ranging domestic cats kill 1.3 to 4.0 billion birds and 6.3 to 22.3 billion mammals annually. Our findings suggest that free-ranging [and unowned] cats cause substantially greater wildlife mortality than previously thought and are likely the single greatest source of anthropogenic mortality for U.S. birds and mammals.”

Unowned cats include farm/barn cats, strays fed by humans but not granted access to habitation, cats in subsidized colonies, and feral cats. Sixty-nine percent of the mortality is attributed to unowned cats, showing their superior prowess and efficiency as hunters.

Their study also showed that between 6.3 and 22.3 billion mammals are killed annually by cats. Free-roaming pet cats were responsible for 221 million to 1.7 billion bird deaths and 512 million to 2.8 billion mammalian deaths. They conclude that between 228 and 871 million reptiles and 86 and 320 million amphibians could be killed by cats in the contiguous United States each year.

Other studies support these disturbing conclusions. The authors of a Wisconsin study report that 39 million birds are killed annually in that state alone. In a Michigan study, 800 to 3,100 cats killed between 16,000 and 47,000 birds during one breeding season. A wedge-tailed shearwater colony in Hawaii exhibited total reproductive failure, with almost all the adult shearwaters at this site were apparently killed by cats.

Canadian cats kill up to 348 million birds a year

In Canada, similar studies done by Environment Canada conclude that cats appear to kill as many birds as all other anthropogenic (i.e. human-induced) impacts combined. Feral and pet cats are believed to kill more than 100 million birds a year in Canada, with an estimated 60 percent of those killed by feral cats.

Collisions with electricity lines have been identified as the second-largest human-caused source of bird mortality in Canada, with 10 to 41 million birds killed annually. Collisions with buildings are responsible for the death of an estimated 16 to 42 million birds annually, and approximately 13.8 million birds are killed in collisions with vehicles.

A 2013 study by Peter Blancher entitled “Estimated number of birds killed by house cats (Felis catus) in Canada,” published in Avian Conservation and Ecology, concludes that cats are estimated to kill between 105 and 348 million birds a year in Canada, with the majority likely killed by feral cats. This conclusion was based on an estimated 8.5 million pet cats and 1.4 to 4.2 million feral cats.

These estimates suggest that between two and seven percent of all the birds in southern Canada are killed by cats every year. They reference previous Canadian studies where B.B. Guthrie, in 2009, estimated that 165 million birds were killed annually. Erica Dunn and Diane Tessaglia, in the Journal of Field Ornithology (1994), attributed 29 percent of bird kills to cats. The Rithet’s Bog Conservation Society reported in 2011 that 22 percent of all attacks on song sparrows were generated by cats.

Guthrie went on to analyze which species and families might be more susceptible to cat predation. He concluded that insular species ( those living on islands and those living in artificially isolated and/or fragmented habitats such as those surrounded by subdivisions) were most prone. In contrast, interior forest species were less likely to be predated. Free-roaming pet cats were more likely to take small songbirds at feeders, while feral cats generally took larger birds.

Twenty-three species at risk in Canada, according to a 2012 report from the Committee on the Status of Endangered Wildlife in Canada (COSEWIC), are among the potentially vulnerable species identified. Among the listed ground-nesting species, three of 11 prairie-nesting species and three of four grass and scrub-nesting species are at risk from cat predation.

Study after study reaches the same conclusion, whether it’s about grey catbirds suffering 79 percent mortality primarily due to cats, seabird populations being wiped out on sub-Antarctic islands, or California quail and thrashers extirpated in a park where cats hunted. Cats were choosing to kill birds and native mammals but avoided non-native mammals (e.g. rats) such that the number of rats in the cat-infested area was nine times higher than in the cat-free zone.

Native predators losing food sources

Why should we care?

Beyond the obvious devastating impacts on wild populations of birds, mammals and herptiles (amphibians and reptiles), there’s a secondary impact on avian and mammalian predators. If the cats kill most of the prey, what’s left for the native predators?

Studies in Maryland showed that the loss of native prey to cats (e.g. chipmunks) resulted in Cooper’s hawks choosing alternate prey and, subsequently, having a much reduced reproductive success rate.

Native predators tend to be in balance with their prey – fewer prey species lead to fewer predators. But this isn’t the case with cats since pets have it all – food, shelter and protection. The pressures that control natural predators don’t affect them the same way and their populations burgeon unchecked.

Unlike natural predators, cats typically kill prey whether they intend to eat it or not, further decimating wild prey populations.

Cats tend to be active in daylight hours when birds are least suspecting since their natural predators are mostly nocturnal. This again artificially raises the kill rate and hunting success of the cats.

And cats are the only predators that typically stalk healthy adult birds by choice rather than taking fledglings and weakened birds.

Cats can become disease carriers

Another emerging issue is also of concern. Free-roaming cats, domestic and feral, act as reservoirs and vectors for many diseases and parasites that may jeopardize wildlife, such as feline leukemia and feline parvovirus.

Most importantly, cats play an integral role in the life cycle of the protozoan parasite Toxoplasmosis gondii, where the cat is a definitive host. T. gondii has infected more than 50 bird species worldwide. The parasite is shed in the feces of infected cats and a broad range of animals (including humans) may act as intermediate hosts and may develop clinical disease as a result of this infection.

Add to this that cats appear to be selectively avoiding rats as prey, should we not be more concerned about vector spread diseases as rat populations increase due to reduced predator pressure?

How do we tackle the problem?

Well, what can be done?

The trap-neuter-release or trap-neuter-return (TNR) movement is well-funded and entrenched as part of the solution for cat problems. Essentially it opposes the use of euthanasia to control cat populations while promoting feeding and sterilization programs.

But evidence suggests TNR isn’t the solution as the sterilization efforts can never be widespread enough to offset the breeding success of non-neutered cats. TNR often leads to perpetual colony maintenance, huge costs, magnified volunteer efforts and even an increase in cat populations as the cats are well-fed and protected by the cat guardians, as witnessed by one program in Hawaii that grew from about 100 to over 1,000 cats.

Many veterinary and animal rights and welfare professionals deem TNR to be inhumane, since it may encourage pet abandonment, as owners of unwanted pets are assured their cat will be well taken care of when released. Clearly, the rights of the wild animals are never factored in when TNR is implemented as hundreds of thousands of wild animals die when these cats persist.

Dog owners are more environmentally conscious of the impacts of their pets, not necessarily due to any awareness of the impacts of dogs at large, but more likely since municipalities aggressively enforce stoop-and-scoop, leash and dogs-at-large bylaws.

That’s not to say cat owners condone the killing of wildlife – likely, they just never think about it.

All dogs are vaccinated for rabies but is this true of cats? Many are, but likely most, particularly feral cats, aren’t.

So what should you do?

Each person has to weigh the facts and decide for themselves. For me, it’s always been easy. I have a 14-year-old cat that has never been out of the house (except to go to the vet for her shots annually) and she’s happy and content. She knows what birds are as she will look out the window at them but never attempts to catch them. The hunting instinct is there but the opportunity isn’t. She seems satisfied just knowing she can do it without necessarily killing something.

Cats can be leash-trained despite popular thought and, if one still insists they must be allowed outside, an enclosure can be built for them, much as one would for a dog.

We won’t solve the conflict here but each time someone chooses nature over their cat’s freedom, many wild things will survive for generations to come.

Geoff Carpentier is a published author, expedition guide and environmental consultant. Visit Geoff online at, on LinkedIn and Facebook.

© Troy Media

The views, opinions and positions expressed by columnists and contributors are the authors’ alone. They do not inherently or expressly reflect the views, opinions and/or positions of our publication. © Troy Media
Troy Media is an editorial content provider to media outlets and its own hosted community news outlets across Canada.