Do you have a citation for this? Are you comparing North American cat deaths to worldwide building collisions? Estimates I'm seeing of North American center around 600 million, a far cry from deaths due to cats.
https://www.nationalgeographic.com/premium/article/birds-win...
>a far cry from deaths due to cats.
No, they are about the same. The 3.5 billion is the top estimate similar to how 4 billion is top estimate for killed by cats. The lower estimates in both cases around 1 billion something.
FWIW 3.5 billion is not the top estimate, although I'm not sure how to interpret the way the estimate is stated ("annual mortality may be minimally 1.28 billion–3.46 billion or as high as 1.92 billion–5.19 billion"). What does it mean to have a range for each end of the range? The author only quotes the absolute lowest number from the study in press about it (see https://www.lehighvalleynews.com/environment-science/3-5-mil...), but maybe is just preferring to be conservative.