Outdoor Cats: A Major Souce of Human-Caused Mortality for Birds and Mammals

by Larry Jordan on January 31, 2013

Cat with American Coot photo by Debi Shearwater

Due to concern about the validity of the original headline of this post, I have changed the title from “Single Greatest Source” to “A Major Source” of Human-caused Mortality. Please read the actual study linked below as “peer-reviewed study”

The following is an excerpt from an article by the American Bird Conservancy (ABC). You can read the full story here.

Washington, D.C., January 29, 2013 – A new peer-reviewed study published today and authored by scientists from two of the world’s leading science and wildlife organizations – the Smithsonian Conservation Biology Institute and the U.S. Fish and Wildlife Service (FWS) – has found that bird and mammal mortality caused by outdoor cats is much higher than has been widely reported, with annual bird mortality now estimated to be 1.4 to 3.7 billion and mammal mortality likely 6.9 – 20.7 billion individuals.

According to Dr. George Fenwick, President of American Bird Conservancy, one of the leading bird conservation organizations in the U.S. and a group that has called for action on this issue for many years, “This study, which employed scientifically rigorous standards for data inclusion, demonstrates that the issue of cat predation on birds and mammals is an even bigger environmental and ecological threat than we thought. No estimates of any other anthropogenic [human-caused] mortality source approach the bird mortality this study calculated for cat predation.”

The study charges that, “Despite these harmful effects, policies for management of free-ranging cat populations and regulation of pet ownership behaviors are dictated by animal welfare issues rather than ecological impacts. Projects to manage free-ranging cats, such as Trap-Neuter-Return (TNR) colonies, are potentially harmful to wildlife populations, but are implemented across the United States without widespread public knowledge, consideration of scientific evidence, or the environmental review processes typically required for actions with harmful environmental consequences.”

You can always get the latest bird news on my “Birds In The News” page!

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{ 9 comments… read them below or add one }

Gail February 1, 2013 at 4:32 am

I saw that article on Twitter and was so sad. Add to this another reason why I dislike cats. Sorry to cat lovers everywhere, but that’s how I feel.


Mia McPherson February 1, 2013 at 9:17 am

I love cats but only if they are indoors.


ingrid February 2, 2013 at 11:41 am

Larry, thanks for posting this. I’ve been looking into this report a bit since it’s getting such wide coverage. I’m troubled by the wording of the actual conclusion drawn from the study — that cats are “likely the single greatest source of anthropogenic mortality for US birds and mammals.” It’s worded in such a way to put emphasis on a single source of mortality (obviously) which tends to minimize collective anthropogenic effects.

What I’ve found so far suggests there might be potential issues with a study of this nature … that the numbers were extrapolated from a small sample, for instance. And that issues like additive and compensatory damages aren’t take into account. So far, most of the refutations are published at cat advocacy sites, so I need to take time to find the original materials. (One such cat advocacy counterpoint is here: http://www.straypetadvocacy.org/html/predation_studies_reviewed.html)

The reason I’m concerned is that although I’m a staunch wildlife advocate, as you know, I fear for the vilification which does and will occur surrounding animals that get labeled as damaging vermin, and what sorts of policies might ensue. I’ve worked in a wildlife hospital where I’ve seen the effects of cat caught birds and other negative human interventions, so I’m not an apologist for what cats do to birds. I believe domestic cats should be indoors or given access to outdoor cat enclosures where they cannot access birds.

But, I have also worked with domestic animal rescue groups, so I’ve seen the other side — and the cruelty inherent in extermination policies is rampant. My view is that reports like this make it easy for people to scapegoat — in the context of global catastrophe and mass extinction event where clearly the combined anthropogenic effects are the most disastrous influence. Without minimizing the effects of predators like cats, I still think it would be more accurate to say that anthropogenic causes are the single biggest source of wildlife mortality, bar none, and not separate the human effects into categories.


Larry February 2, 2013 at 10:16 pm

@ Mia I concur

@Ingrid I understand your points and I agree that we humans are the largest cause of wildlife mortality on the planet. The feral cat problem is actually one caused by we humans as well. It is caused by people that don’t spay and neuter their pets. The problem with trap-neuter-return (TNR) programs is that they can never catch all the cats and their offspring that we humans have released into the wild.

Cats are very prolific. They can have 3 litters of 3 to 6 kittens each per year! Starting at just 4 months of age, a female cat (still a kitten herself) can have her first litter. You can see how these numbers can explode into an unmanageable situation.

So the problem, as I see it, is that we have millions of unwanted cats roaming free. Unwanted cats that will keep reproducing, no matter how many are trapped and neutered.

According to the Humane Society, 70% of cats taken to shelters are euthanized. More than 12 million dogs and cats are euthanized in pounds and shelters across the country every year. This is disgraceful! All because people don’t spay and neuter their pets.

My solution is to spay and neuter your pets and keep your cats indoors. And if you can’t take care of a pet, don’t own one.


Ingrid February 3, 2013 at 12:07 am

Hi, Larry, thanks for the reply. I couldn’t agree more about spay/neuter … and your points are all valid, as are the arguments about cats harming birds. I also advocate for indoor cats, and for safe, attached outdoor cat enclosures for those who want their cats to have some sun. I am in total agreement about the solution. The irresponsibility of many pet owners drives this whole issue for sure, and it is, indeed, disgraceful.

I just worry, admittedly, about studies like this fueling the existing hatred for cats in such a way that results in misguided policies. I’ve had discussions at a birding board where a person advocating for the torture and slaying of all outdoor cats ( to protect birds), collared or not, was met with tacit acceptance instead of the revulsion his cruel comments should have inspired. That makes me exceedingly cautious about baiting that hatred, when, as you say, cats are just one facet of largely anthropogenic harm.

I guess what I’d like to see is the cumulative number which includes window strikes (a billion, I’ve read), poisons, cars, electrocution, habitat destruction, hunting, traps, plastics, fishing nets, etc. I guess I’d feel less resistant about the cat issue if I saw more due diligence in ridding our landscape of these effects at the same time. They are all critical but it sometimes seems that non-native species take the brunt of our negligence.


Ingrid February 3, 2013 at 12:18 am

p.s I think we should have a comprehensive, legislated spay/neuter system that’s much more rigorous than what we have now — for the welfare of pets and wild birds. Some animal advocacy groups have tried, but breeders and pet industries fight it at every turn. We should have severe penalties for dumping cats, etc. And I would support an indoor cat rule, too. There just aren’t enough deterrents for people who want to behave badly. I wish volitional measures worked.


Larry February 3, 2013 at 6:48 am

@Ingrid well stated! I have not delved into this problem but I know that organizations like the American Bird Conservancy (ABC) has been fighting for solutions for many years. I did a bit of research before addressing your last comment and read (can’t recall the source) that window strikes kill more birds than do cats. I guess it all depends on your statistics, which gets back to your original argument. Either way, since most causes of bird death are anthropogenic, we should work to fix those problems. As for the idiot that suggested slaying of all outdoor cats, it saddens me to know that there are people in the world like him.

I guess we shouldn’t even touch on the number of birds killed by the US Department of Agriculture’s “Wildlife Services” to protect grain crops?


Wally February 3, 2013 at 8:50 am

Good post, Larry, and informative follow-ups. It does seem to come down to humans taking responsibility. An age-old problem with no easy solutions.


ingrid February 3, 2013 at 12:17 pm

Larry, I won’t name any of those guys and give them undue publicity, but there’s one notorious cat hater/bird lover (although his true affiliations are questionable) who posts on just about every birding blog, advocating for brutality to cats. He levels ad hominem attacks on anyone who calls him out, and I’m thinking he’s got a 24/7 notification system for these cat/bird stories that’s more powerful than Google alerts and which send him into paroxysms. 🙂 I think everyone can see he’s unbalanced, but I’ve seen some birders actually side with him because he’s advocating against cats. I worry when I see that type of visceral reaction.


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