More scientific evidence has surfaced to show that while mittens may be your sweet angel, letting her roam outside is also a big threat to biodiversity.
I had two cats from the same litter. The female was superfocused on birds, rarely paid any attention to mice or voles which are pretty abundant here in the countryside. She very rarely managed to catch any birds in the wild, but if one made the mistake of flying into the house, it was game over in seconds. She could jump surprisingly high.
The male on the other hand was only interested in rodents. It was like to him birds didn't exist. For yeard he kept our house totally free from mice, roaming the yard and doing his thing very effectively. I'd pay good money to have a cat like him again.
I wouldn't let my cats out in the city, but out here I'll let them live by their insticts. The nearby highway kills a lot more birds and mammals daily than they ever could.
They very obviously weren't talking in total across the US. Just their property and their nearby highway. I find what they said to be quite believable even with the total amount of birds cats kill across the US
Anecdotes are not data, however. They might think cars kill more, but data shows that nationwide, the opposite is true by an order of magnitude.
You see birds killed by cars on the road because the dead birds stay where they’re hit. You don’t see the ones killed by cats because cats don’t usually leave them there.