The UK’s largest bird charity, the Royal Society for the Protection of Birds (RSPB), is not particularly concerned about the impact of cats on the British mainland. Instead it focuses on what it says is driving UK bird declines: global warming, intensive agriculture and expanding towns and cities leading to habitat and food loss. “While we know that cats do kill large numbers of birds in UK gardens, there’s no evidence this is affecting decline in the same way that these other issues are,” said a spokesperson.
I agree that the environmental changes are affecting birdlife as well.
But even taking the lower end of the estimate of the number killed by cats, 40 million birds each year is a felt loss. The RSPB may opine as they wish, but that's the data.
Anecdotally, my neighbour's cat is known to bring home as many as three birds on some weeks. I've seen them stalk my bird table using the bushes as cover. Data + eyewitness observation makes a compelling case.
If you read the article, they actually argue that the cats don't really have an effect because those 40 million birds are usually of species that aren't endangered and are usually birds that otherwise wouldn't have made it anyway.
Though 40 million dead birds sounds like a lot, in regions where wildlife had millenia to adapt to cats' existence – in continental Europe cats have existed for tenthousands of years – it’s not a significant issue.
And it's sad that so much time and energy is wasted on this discussion when people are still spraying their own backyards with pesticides and destroying "weeds", which are actually necessary for insects, and as result birds, to thrive.
We've got to be really careful with those numbers. There's a massive difference in the ecosystem between continents. While we've become used to flora and fauna from continental Europe being brought to the rest of the world, that doesn't make them native there.
The issue in the report you linked isn’t cats living outside, the issue here is european flora and fauna existing at all in the US, where it doesn’t belong. This issue isn’t limited to cats, it even includes things like different species of lawn grass being invasive in regions it doesn’t belong.
The UK’s largest bird charity, the Royal Society for the Protection of Birds (RSPB), is not particularly concerned about the impact of cats on the British mainland. Instead it focuses on what it says is driving UK bird declines: global warming, intensive agriculture and expanding towns and cities leading to habitat and food loss. “While we know that cats do kill large numbers of birds in UK gardens, there’s no evidence this is affecting decline in the same way that these other issues are,” said a spokesperson.