Thank you for the well-sourced reply.

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.

>The implication is that just because birds are dying, it's okay to snatch a cat.

the implication is that if you want a cat, you should be responsible and keep it indoors.

>But again, the cost here is "removing, by force, someone's beloved pet."

no, the cost is keeping your cat indoors.