The Science of Birds - Cats vs Birds

Episode Date: February 24, 2021

Join Ivan as he wades into the conservation quagmire surrounding house cats and their effects on wild birds.First, we’ll look at the status of house cat and feral cat populations around the world. How are all these free-ranging cats affecting our wild birds? Many scientific studies of this issue give us some answers. Research also provides guidance for how best to solve the problems that cats create for birds. Some approaches are more severe than others.We’ll also go over a few ways that responsible cat owners can help protect their local birds as well as keep their kitty happy.~~ Leave me a review using Podchaser ~~Links of InterestFurther Reading: The Moral Cost of CatsCatio Tours in Portland, OregonLink to this episode on the Science of Birds websiteSupport the show

Iceland was first settled by Norwegian Vikings in about the year 870, 870. Besides livestock like cows, horses, and sheep, these people brought with them some domesticated cats. Cats were popular in Scandinavia for their effectiveness at keeping rodent populations in check on farms. Before Viking ships landed on its shores, Iceland's only native land-dwelling mammal was the Arctic fox. So humans, farm animals, and cats were all alien invaders on that isolated island in the North Atlantic. Fast forward about 1,100 years and you find me, looking at a black and white house cat in Iceland's biggest city and capital, Reykjavik. I was there leading a birding slash nature tour not that long ago. My group and I were doing some light bird watching in a large

downtown park, enjoying waterfowl in the ponds and songbirds flitting around in the trees. One pond has a tiny man-made island in the middle. The island was landscaped specifically to serve as nesting habitat for Arctic terns. In summer, it teems with dozens of turn chicks and their devoted parents. The Arctic Turn, Sterna Paradisia, is a graceful white bird in the family Laredi, which includes turns and gulls. It has a black cap and a sharply pointed bill the color of blood. Every year, these birds make a round-trip migration to the waters around Antarctica and back to the far north. That's about 25,000 miles or 40,000 kilometers every year.

So there I was in Reykjavik with my group looking at the turns, when a cat caught my eye. It wasn't on the little island, thankfully, but on the grassy shore of the pond. The cat was jumping in the air acrobatically, swatting at Arctic turns. Several turns were swooping back and forth just out of reach over the cat's head. This is what they do. These birds aggressively dive-bom any predators near their nests. And they can't always distinguish well-meaning birders from predators. It's sort of a rite of passage for birdie.

in Iceland to get swooped and maybe pecked in the head by an angry Arctic turn. I can tell you from experience that these small birds pack quite a punch, or peck quite a punch, I guess. To me, the sound of screaming turns is as iconic of Iceland as thundering waterfalls and the music of Bjork. This is the last thing you hear before getting stabbed in the cranium by a turn. The scene of that cat leaping at the turns was almost comical. Witnessing this scene on a sunny summer day in a beautiful park, you might smile or laugh. Oh, what a silly kitty. But situations like this are matters of life and death for the birds.

If the cat got its claws into one of those turns, the bird would be killed. In the short time we watched it, the cat wasn't able to take down a turn, thankfully, but Maybe it got lucky later that day. And what about all the other cats in the city, doing their best to catch birds day after day, year after year? Reykjavik is now famous and even celebrated for its large population of cats. About 20,000 feline fuzz wads prowl the streets of this fairly small city. They're mostly free-roaming pampered pets that have warm homes to return to every day.

But the cats of Reykjavik routinely kill and bring home songbirds like red wings, common red poles, European blackbirds, and meadow pippets. The organization BirdLife, Iceland, implores cat owners in Reykjavik and elsewhere in Iceland to keep their feline friends indoors, at least during the breeding season when birds are most vulnerable. But you have to wonder how many of those cat-owning Vikings even hear the plea made by birds. BirdLife, Iceland, much less do what it asks. Iceland is just one minor battlefront in the worldwide war of cats versus birds. Hello and welcome. This is the Science of Birds. I am your host, Ivan Philipson. The Science of Birds podcast is a lighthearted, guided exploration of bird biology for lifelong learners.

Today, we're wading into the conservation quagmire surrounding house cats and their effects on wild birds. I'll do my best to present this issue from an objective, scientific perspective. Sure, my personal feelings will leak through here and there, but most of what I want to give you are the cold, hard facts. It's really important that I preface all of this by saying that I say that I should. love all animals, including spiders, mosquitoes, leeches, and yes, even cats. I grew up with several pet cats and they were wonderful. These days, I'm mildly allergic to cats, but if I wasn't,

I might have one curled up beside me right meow. Furthermore, I think kittens are way cuter than human babies, and I've spent an embarrassing number of hours, perhaps even days or weeks of my life watching ridiculous cat meme videos. I think cats are hilarious and adorable and amazing. Is that enough to convince you that I don't hate cats? I hope so, because most of what I have to say about them in this episode isn't good. From the perspective of wild birds, from what science tells us, cats are pretty much the worst. The domestic cat, Phyllis Kattis, traces its origins to the Middle East.

Its ancestors were European wildcats, Phelis Silvestris, that were skulking around in the fertile crescent about 10,000 years ago. These wildcats started preying on rodents infesting human farming settlements. The farmers took notice and welcomed the reduction in grain-eating mice and rats. And so began our long history with pet cats. Another species, the African wildcat, Phyllis Libica, eventually mingled with domestic cats in ancient Egypt, adding some novel genetic material into the mix. Cats spread across the ancient Middle East, northern Africa, and the Mediterranean with their human owners. By the end of the Roman Empire in about

the year 500, domestic cats were all over Europe. Their popularity as pets continued to rise over the centuries. Distinct breeds and breed standards were developed starting in the 1800s. So, thanks to cat fanciers, we now have breeds like the ragamuffin, Aphrodite giant, Australian mist, and Spanish hog neck. One of those isn't real, but how could anyone tell? In the last few hundred years, cats have been introduced to just about every corner of the planet. We've dropped cats into countless locations where they never existed before. Many of these places had no native felines at all, and some remote islands had no mammals whatsoever. Do you think that birds in those places possessed natural defenses against cats? Not so much. Today, there are roughly 96 million

pet cats in the United States. That's about one cat for every 3.5 people. The estimate for China is approximately 100 million pet cats. For the UK, it's between 8 and 11 million, and Australia has about 4 million. Now, we're talking about house cats here. These numbers are for cats that live with and are cared for by people. But there are feral cat populations all over the world. These are free-ranging cats that live on their own. Feral cats aren't socially bonded with humans. If you tried to pick one up for a cuddle, you might get your eyes scratched out. Estimates for the feral cat population in the U.S.

range from 30 million to over 100 million. This means there might be more feral cats in this country than house cats. There are perhaps 1 million feral cats in the U.K. and two to six million roaming around in Australia. So there are a lot of cats out there in the world, both owned and unowned slash feral. How have all these furry little murder machines affected the populations of birds?

Let's consider that next. Spoiler alert, cats kill birds. Actually, we all know this, right? Cats are small carnivores that eat meat and only meat. They're ambush predators that rely on stealth and quick reflexes to catch their prey. If you've had a pet cat, you probably know from firsthand experience how their teeth are like stabby needles and their claws are like fish hooks. When roaming freely outside, a domestic cat is an opportunistic hunter.

It catches and makes a fancy feast out of whatever, small animals happen to be around. These could be birds, but if there are more rodents around, cats might eat more rodents. Depending on which region of the world you're looking at, the cats there may prey mostly on insects or frogs or lizards. Even well-fed cats kill birds and other animals. This behavior is a deeply ingrained instinct. If you've ever owned a free-ranging cat, you've probably received a so-called gift from your kitty, a dead mouse, bird, or lizard. Many scientific studies have actually used these morbid gifts as data to quantify the numbers of prey animals that house cats kill. In some studies, researchers have asked cat owners to keep

track of the numbers and types of small animals brought home by their pet. But how many of the animals that cats kill actually end up on our doorsteps. Several studies have ingeniously used kitty cam video cameras to monitor what cats do when they're off roaming around. These are small GoPro-style cameras worn on the collar, so they're kind of like the body cams worn by police officers. A kitty cam records what a cat sees and what it does. Some cat owners who participated in these studies were horrified to see the video evidence of carnage caused by their precious Mr. Whiskers when no one was watching. Research using kitty cam videos tells us that cats bring home only about 25% of what they

kill. For every decapitated sparrow your cat drops in your foyer, or foyer, as some of you might say, for every one bird you see, there are three more dead birds that you'll never see. This and other research provides us with estimates of how many birds each cat kills. On average, each free-roaming house cat in North America and Europe kills between 30 and 50 birds per year. Not all birds are equally vulnerable to cat predation. Small birds that forage or nest on the ground are killed more frequently. And perhaps not surprisingly, birds that visit backyard feeders are also more likely to get jumped by cats. Cats don't have to outright murder birds to have a negative effect on their populations.

Research shows that cats can have indirect sub-lethal effects on birds. For example, if a cat is lurking around, nesting birds might, out of fear, make fewer foraging trips to find food for their chicks. So the chicks won't grow as quickly or end up as healthy as they might otherwise. The mere presence of cats can scare birds away or cause them excess stress. This makes intuitive sense, right? I mean, imagine if the population of mountain lions in North America was the same as the population of house cats. That would be about 2,000 times more mountain lions than there are right now. These 200-pound beasts would be lurking around every corner

waiting to pounce on you. Even if you weren't eaten directly by a mountain lion, fear of that prospect would probably make you think twice about taking your daily walk to the corner market to buy two lukewarm corn dogs and a red bull. Some researchers argue that the sublethal effects of cats have larger impacts on bird populations than all the direct killing. But to date, relatively few studies have assessed sublethal effects, probably because these are a bit challenging to measure. So there are millions and millions of cats out there, frolicking and frisking about in cities, suburbs, and the countryside. Besides whatever sublethal effects they're having on birds,

each cat is killing dozens of our feathered friends each year. What is the net result? What's the damage? Well, in the U.S. and Canada, cats are the number one, the No. Uno cause of direct human-related mortality in birds. So cats are way worse than window or car collisions or wind turbines. A widely publicized study from 2013 estimated that up to 4 billion birds are killed by cats in the United States every year. 4 billion every year. That's insane.

Another study from 2013 estimated that in Canada, cats kill up to 3,000. 350 million birds each year. These numbers are estimates, and there's a fair amount of uncertainty around them. But it's safe to say that across North America, at least a billion birds are slaughtered every year by cats. That's the conservative estimate. One example of a North American bird species getting hammered by cats is the piping plover, Corradius Melodos.

This lovely little shorebird feeds and nests on the ground on wide beaches. Feral cats pick off both the adult birds and their chicks. Are cats the only threat to these birds? Absolutely not. Humans have done all sorts of stupid things that hurt piping plover populations. Cats are just part of the equation. Also, if I look at a kid, kitten side by side with a fuzzy piping plover chick, the cuteness is too much. I can't decide which

of these two soon-to-be mortal enemies is more adorable. I just wish they could coexist in harmony. Anyway, study after scientific study has revealed the same pattern around the world of cats causing large-scale destruction. A recent study in China estimated that between 2.7 and 5.5 billion birds are killed by free-ranging cats every year. In Australia, pet cats and feral cats together kill something like 375 million birds a year. That sounds like small potatoes compared to what's going on in North America and China, perhaps.

But keep in mind, 375 million birds a year amounts to over 1 million birds being killed every day. That's a big deal. New Zealand has the highest per capita rate of cat ownership of any country in the world. They've got about 1.5 million house cats. It's estimated that these cuddly kitties slaughter 19 million birds a year.

They also kill huge numbers of native lizards like geckos and skinks. Speaking of New Zealand, I could devote episode after episode to covering the saga of how invasive species in that country have decimated the native birds. But for the moment, let's talk briefly about the Stevens Island Renn, Traversia Laili. Stevens Island is a tiny chunk of land a couple miles off of New Zealand's coast. In the 1890s, a lighthouse was erected on the island, along with a few homes for the lighthouse keepers. One of the new human residents on the island brought with them a cat, a cat named Tibbles, so the story goes. She was the first cat ever to set foot on Stephen's Island.

Tibbles may have arrived already pregnant with kittens because before too long there were feral cats all over the place. Tibbles, the cat, had a habit of bringing dead birds to one of the lighthouse keepers, David Lyle. He was an enthusiastic amateur naturalist with an interest in birds. Lyle soon figured out that one of the bird species Tibbles was bringing him had never been seen or recorded by Western scientists. It was a tiny brown bird with short wings, a short tail, and large feet.

He preserved some of these little birds and sent the specimens off to ornithologists. This new species came to be known, eventually, as the Stevens Island Wren. It was in the same family as the Rifleman and South Island Wren. Notice I said, was there. Past tense. In just over a year after Tibbles made landfall on Stevens Island, Lyle stopped seeing any of these little wrens. No one saw them. The cats had absolutely devastated the bird fauna of the small island, and they drove the Stevens Island Wren to extinction. This bird was flightless, one of the few flightless songbird species in the world,

actually. That trait made it especially vulnerable to cats. All that remains today of the Stevens Island Wren are David Lyle's 15 specimens, resting lifelessly in several museum collections. If you've listened to more than a few Science of Birds podcast episodes, you've probably heard me talk about birds on islands quite a lot. There are several reasons why islands keep coming up, one of which is that island birds are often extra vulnerable to invasive predators. So while the story of the Stevens Island Wren is an extreme example, similar events have played out on islands around the world. And there are battles raging right now between birds and introduced cats on islands everywhere. At least 90 species of island-dwelling birds today face the ongoing

threat of feral cats. Cats have been a major factor in the extinctions of at least 40 bird species in the last few hundred years. Most of those birds were found on islands. Mr. Kitty and his furry buddies helped to obliterate birds like the Bonin wood pigeon of Japan, the red rail on the island of Mauritius, and the Guadalupe Caracara in Mexico. I'm sure you get the point here. Cats bad, birds good. Okay, it's not as simple as that, is it? But that's probably how birds would assess the situation. Free-ranging cats are pretty bad news for wild bird populations. So what's being done about this? How have conservationists tried to help birds in the face of this feline onslaught? Let's get into all of that now.

There are many efforts being made around the world to reduce or eliminate the threat of free-roaming cats. Conservationists have taken several approaches, some more extreme than others. As you can imagine, very different approaches are used for dealing with house cats versus feral cats. For house cats, the freeloading fur balls that live with people, one of the few things conservation organizations can do is run campaigns that encourage people to be responsible pet owners. Cat owners are asked to please keep their kitties indoors and to de-sex them. De-sexing helps reduce the number of unwanted cats that end up feral or in shelters. Conservationists implore cat owners who insist on letting their cats outside to at least put special collars on them,

or bells. These devices make it harder for cats to sneak up on birds. I'll circle back in a few minutes to some things responsible cat owners can do to keep their pets happy and to keep birds safe from them. Sometimes actual laws are put in place to control the populations and damaging effects of cats. For example, pet cats in the states of West Australia and South Australia are required by law to be desexed. The state of Rhode Island and Los Angeles County in the U.S. similarly require most pet cats to be desexed. Now, what about all those feral cats? There are more options for dealing with them since they don't actually belong to anyone. But there's also more controversy around the management of feral cats. The answer to the question, how should we

approach the feral cat problem depends on who you're asking. Some people are like, what feral cat problem? Feral cats are wonderful. If there is a problem, it's that there aren't enough feral cats. More feral cats. More feral cats. But most organizations, even those that are heavily biased towards the welfare of cats, recognize the need to control feral populations. To that end, organizations like Alley Cat Allies and the Humane Society champion the trap-neuter return approach. TNR, not to be confused with GNR, Guns and Roses, TNR programs involve catching feral cats, desexing them, and then tossing them back out into the alley or junkyard or wherever.

This approach is popular and considered a humane way of reducing feral cat populations, or at least a way of keeping them from growing. Are trap-neuter return programs actually effective in reducing feral cat populations? Advocates of such programs will say, yes, they are. But really, there still isn't a lot of reliable scientific data to tell us how effective or ineffective the TNR approach is. In some cases it works and the cat population decreases. In other cases, it doesn't work.

At least theoretically, desexing most of the cats in a feral population would result in fewer cats over time because the death rate due to old age or whatever would outpace the birth rate. But this assumes a closed population with no immigration from the outside. Feral cat populations are rarely closed systems. except for maybe on small isolated islands.

In most places, new cats join the population from the outside, either on their own or with the help of people. One study based on computer simulation modeling suggested that TNR programs should work well for small local populations with less than 50 cats. Larger populations, however, are much harder to manage with this method. Now, I am by no means an expert on this TNR stuff. I'm just presenting a little of what I've gleaned from the scientific literature.

Hopefully, additional rigorous research on this topic will give us better answers for when and where we should apply the trap-neuter-release approach. For many conservation organizations that focus on protecting wild birds and other wildlife, TNR isn't enough. These organizations endorse a more forceful approach. They say, Kill the kitties, shoot them, trap them, poison them, whatever it takes to get rid of feral cats. Sound harsh?

Yeah, it is harsh. But that doesn't mean it isn't effective. Many argue that this approach is a necessary evil that gets the job done. Feral cat eradication by targeted killing is endorsed by Pete Mara, the head of the Smithsonian Migratory Bird Center. Like me and perhaps you, Mara loves both birds and cats. But he argues that killing feral cats is, at least sometimes, the necessary thing to do. He wrote an entire book about this problem titled Cat Wars, The Devastating Consequences of a Cuddly Killer.

Where cat eradication makes the most sense and where its most effective is on islands. Once cats are eliminated from a small island by killing and or relocation, it's possible to keep new ones from showing up. Studies have shown that dozens of cat eradication programs have been successful on small islands across the globe, from those off of New Zealand and Australia to Mexico, Ecuador, Fiji, and islands owned by Spain, France, the UK, and the United States. Threatened bird populations often rebound after invasive cats have been removed. One example is the black-vented shear water in Mexico. About 95% of all black-vented shear waters breed only on Isla Natividad,

a tiny island off the coast of the Baja Peninsula. After cats were eradicated from the island in the early 2000s, shear-water mortality there dropped by 90%. Does the thought of killing cats make you cringe? If so, you're not alone. Those of us who love animals find no pleasure in the idea of shooting or poisoning cats. But from a scientific, objective point of view, if our goal is to protect and conserve wild birds, there are situations where our most effective way to achieve that goal is to eradicate feral cats by killing them. There are many scientific ways to look at this war between cats and birds, like the data and

research we've been talking about. But there are also huge ethical and moral issues swirling around all of this. This podcast is called the science of birds, not the ethics of birds. So I won't go too deep into questions of right and wrong. Science can provide us with some useful data to inform our decisions, but those decisions are, ultimately, subjective. We make them based on our values. So what do you think? Do wild birds have more value than cats? Or is it the other way around? Perhaps your answer will depend on which cats we're talking about, because of course your cat has more value than most humans, not to even mention birds. And here's something to think about. What about eradicating other invasive animals.

If you object strongly to the whole Kill the Kitty's method of operation, do you feel the same about killing feral goats on the Galapagos Islands? Is that okay? What about trying to eradicate invasive snakes, slugs, or mosquitoes? I could be wrong,

but I imagine a lot fewer people are concerned about killing creepy crawlies like reptiles, rodents, or insects. I'm just saying. Okay, let's say you love birds and you're also the proud owner of a cat or two, or 12. What are some things you can do to protect birds as well as keep your kitties happy and healthy? For the sake of birds, far and away, the best thing you can do is keep your cat indoors. This is actually good for your cat, too.

The Humane Society says this about keeping your cat inside. Quote, indoor cats live longer, tend to be healthier, and can avoid some of the predators, injuries, parasites, and communicable diseases to which outdoor cats may be exposed. End quote. If you want to give your cats some fresh air and some quasi-outdoor exposure, you can build them a cattio. It's like a patio, but with cats.

This is an area enclosed with fencing that keeps the cats in but is still open to the elements. I live near Portland, Oregon, and there are actually organized cateo tours in the city every year. I kid you not. I'll link to some photos of these cateos in the show notes. Some of the designs are pretty impressive. Contrary to popular belief and to my own experience, it is possible to train your cat to walk on a leash. A cat on a leash is not only hilarious, the little monster will also have a really hard time catching birds. When I was about seven, I put a leash on my black cat named Midnight. I thought she and I would have a nice walk around the neighborhood.

Well, Midnight wasn't having it. She flopped around like a fish having a seizure, and the walk was more of a very brief drag. Sorry, midnight. Anyway, with patience, you can, probably get your cat to behave nice. while being led around on a leash. There's lots of information online about how to do this. So I really encourage you to keep your cats indoors, maybe make a cateo for them,

and leash train them so you can drag, I mean, walk them around. If I had a cat, those are some of the things I would do. But if for some reason you feel your cat just has to be allowed to roam around freely, unrestrained, then you can still help birds by accessorizing your cat before it slinks out the door. The more traditional method is to attach a small bell to your cat's collar. The idea is that the tinkling bell will alert birds to the presence of your sneaky little puss-puss, thus eliminating the cat's element of surprise.

Do bells work? Some research says yes, some says not so much. Luckily, there's a better solution that is more likely to work. This is a product called the Birds Be Safe Collar Cover. It's a big disc of gaudy, colorful fabric that attaches to your cat's collar. Birds have excellent color vision. They can usually see a cat wearing a Birds Be Safe collar from a mile away, so to speak. More than one scientific study has shown that these silly-looking devices

not only make a cat look like a sad little circus clown, they are also really effective at protecting birds. One recent study published in the Journal of Zoology tracked 19 cats on the Isle of Man in the UK. Over the four-week study, cats wearing Birds Be Safe collars brought home significantly fewer dead birds than cats that weren't wearing collars.

The reduction in the number of birds killed was about 78%. Besides slapping one of these wacky clown collars on your free-roaming cat, you can do a couple more things to minimize the devastation wreaked by your pet on the local bird population. One is to just play with your cat regularly. Cats are smart and curious, and they need stimulation. Cats seem to kill birds sometimes just out of their need to play.

So get yourself a laser pointer and have at it. Help your cat get all that murderous energy out of its system. What you feed your cat also matters. Some recent research suggests that making sure your cat's diet is rich in meat protein can reduce its instinctive drive to kill birds. Finally, if you have a backyard bird feeder, be sure to place it where cats can't easily pounce on the birds. Keep feeders high off the ground and away from any bushes or trees where a cat might lurk. As bad as free-roaming cats are for wild birds, we can't really blame them for their behavior. I mean, players gonna play and cat's gonna cat, right? They don't know they're bad,

they're just following their feline instincts. The real culprit here is, as usual, humans. We are the ones who have shipped cats around the world. We abandon them, let them reproduce haphazardly and give them free rain to kill wildlife in our backyards and in sensitive natural areas. And humans often do worse things than spread cats around. For most

birds, the biggest threat they face is habitat destruction caused by people. So even though Phyllis Catus is among the most pernicious of invasive species, one could argue that Homo sapiens is the worst

invasive species of all. As we try to reverse the damage we've done, as we try to help birds and the countless other small animals that cats like to kill, we have our work cut out for us. Some of the decisions we make along the way will be relatively easy. Like, should I desex my cats by getting them spayed and neutered? Or, what color of leash should I buy for Princess Razor Clause, my furry little BFF? But other decisions will be more difficult.

For example, to protect the birds of our local nature park, should we choose the trap-neuter return approach to eliminating feral cats, or an eradication program with targeted killing? How effective is each method and what are the ethical concerns? And some of the toughest decisions will be the most ludicrous. Like, how will we decide which is cuter? A piping plover chick, or a six-week-old kitten? I mean, do we really have to choose?

Can't we all just get along somehow? Thanks so much for listening today and for your interest in learning about birds. I'm happy you joined me on this exploration of how cats affect birds. If you haven't subscribed to the Science of Birds podcast, you might want to do that so you don't miss any new episodes. That might help alleviate your phomo, your fear of of missing out. If you'd like to share some thoughts about the show, or if you're a cat lover and you'd like to send me death threats for even mentioning cat eradication, the address is Ivan at scienceofbirds.com. You can check out the show notes for this episode, which is number

23 on the science of birds website, scienceofbirds.com. I'm your humble host, Ivan Philipson. Thanks again and I'll see you on the next episode. Cheers. Thank you.