This is a widely-cited myth, and almost impossible to measure in practice. What does "all the local wildlife" even mean? Is the threat here that birds are going to go extinct because of cats? Not likely, and the burden of proof is on the people repeating this mistaken belief.
Using "think of the birds" as a justification for imprisoning your cat for their entire lives is also pretty crummy. It's called wildlife because they exist in the wilderness. Even if cats kill a large number of birds, so what? Those birds don't have a happy, loving home with emotional bonds to an actual human.
If you think this logic is flawed, explain why you're fine with flies dying but not birds. I bet you've swatted a few in your time.
> Free-ranging cats on islands have caused or contributed to 33 (14%) of the modern bird, mammal and reptile extinctions recorded by the International Union for Conservation of Nature (IUCN) Red List [1]
Cats are probably a leading cause of mortality in birds. [2] Domestic cats are not native to North America. The birds here would not have evolved to avoid them (and beyond that, domestic cat numbers are not limited by prey availability because they're pets bred and fed by humans).
You'll find plenty of studies with evidence that domestic cats are probably bad for bird populations. [3][4]
But to be fair, buildings/glass windows kill a lot of birds too. [5]
Suppose it's true that cats are bad for bird populations. The implication is that just because birds are dying, it's okay to snatch a cat. More than that, that cats should be imprisoned for their entire lives, when they naturally want to roam.
Someone can take one side of this ethical debate or the other, and both sides probably won't agree. I personally find it sad that people would place the well-being of birds above that of a wonderful, furry companion that clearly belongs to someone.
The logic also doesn't quite line up: I was hoping someone would try to justify why it's okay to kill flies but not birds, since that's the real counterargument to this one. Especially when they kill flies with their own hands.
So much of life boils down to "we're the apex species and we do what we want." But such is life. I find it difficult not to call out the absurdities when they appear, though.
To the topic at hand, how exactly is this quantified? I suspect that word "contributed" is doing a lot of work here. [2] seems to admit as much:
> True estimates of mortality are difficult to determine. However, recent studies have synthesized the best available data to estimated ranges of mortality to bird populations in North America from some of the most common, human-caused sources of bird mortality.
The numbers in [2] are admittedly pretty startling. But it looks like they come from one report labeled "2013a". Any info on where to find it, or what it even is? Otherwise it's easy to call [2] a citation when in fact no evidence whatsoever is being presente.
[4] is much better. https://wildlife.onlinelibrary.wiley.com/doi/10.1002/wsb.737 But cats are still only a contributory factor, not the main cause; the report says they're the second leading cause of admissions, not the first. So, high, and worth thinking about.
But again, the cost here is "removing, by force, someone's beloved pet." I'm not above saying that we should probably care about cats more than birds, because of the emotional bonds they form with humans. After all, that's why we're fine with flies being killed, right? No emotional bonds.
> The implication is that just because birds are dying, it's okay to snatch a cat.
I don't think anyone's implying that? It just seems foolish to let your cat roam about. Not only are they at risk of getting stolen, but the risks of getting injured/killed or sick (or poisoned) are so much higher than if you keep them at home.
Whenever I hear about someone who's distraught about an outdoor cat of theirs that died while outside, I feel super bad for the cat, and not quite so much for the owner. That death could have been prevented, trivially.
I believe the Loss et al. 2013a numbers from [2] come from [1] Scott R. Loss (2013).
And, sure, you can look up some other studies [6] that will make you question the accuracy of the numbers but, even if you decrease the estimate by 70%, cats are still killing a lot of birds. Instead of #1 on the [2] list maybe they're #2 (behind buildings).
It's very easy to give a cursory search and see overall North American bird populations are decreasing. Heck, even flying insect biomass is significantly down.
We don't care about people killing flies in their house. We do care about flies dying on a mass scale. Flies are important pollinators! Ecosystems need them.
A few cats killing a few birds is no big deal. Millions of cats killing hundreds of millions of birds, in an ecosystem that shouldn't have cats, is a big deal.
If we armed every American human with flyswatters and sent them outside every day with orders to kill every flying insect they saw then it would probably be very bad (though I think this imagery is also hilarious).
I don't really want to get into my full opinion on the ethics and morality of pet ownership. Stealing other people's pets is wrong. I think if one lives in North America and feels their cat needs outdoor time then it should be supervised on their own property or train it and walk it with a harness and leash. Catios are neat too.
In my neighborhood some people let their cats run around loose. Then the local wildlife (coyotes) eats the cats, and the idiot cat owners whine that the city needs to "do something" about the coyotes.
Pet cats, despite their valued role as companion animals, are a major threat to wildlife. Collectively, roaming pet cats kill 546 million animals per year in Australia. As such the management of cats has major implications for Australia’s wildlife and ecosystems. [...]
Many owners believe their cats don’t hunt because they never come across evidence of killed animals. However, studies of pet cats using video-tracking collars or scat analysis have established that the vast majority (85%) of the animals killed by pet cats are not brought home.
On average, each roaming, hunting pet cat kills more than three animals every week. The numbers add up. On average, over a year each roaming and hunting pet cat in Australia kills 186 animals. This number includes 110 native animals (40 reptiles, 38 birds and 32 mammals). [...]
[For example] In Mandurah, Western Australia, the disturbance and hunting of just one pet cat and one stray cat caused the total breeding failure of a colony of more than 100 pairs of fairy terns. [...]
The findings presented here are summarised from an analysis of the results of many dozens of studies that was undertaken by the Threatened Species Recovery Hub. The research team included scientists from The University of Queensland, The Australian National University, Charles Darwin University, The University of Sydney and Murdoch University. The research received funding from the Australian Government through the National Environmental Science Program and was published in Wildlife Research.
Using "think of the birds" as a justification for imprisoning your cat for their entire lives is also pretty crummy. It's called wildlife because they exist in the wilderness. Even if cats kill a large number of birds, so what? Those birds don't have a happy, loving home with emotional bonds to an actual human.
If you think this logic is flawed, explain why you're fine with flies dying but not birds. I bet you've swatted a few in your time.