I'm not here to tell you I know the absolute truth on the matter, but I can say definitively that your assertion of this fact extends beyond conclusive data. Cats decrease rat sightings, but urban rat populations are good at evading them [1, 2]. Where cats do prey on rats, it's usually juveniles with ultimately little effect on local populations [3, 4].
It's easy to imagine that a certain percentage of the birds cats are killing are ill or old. Yet in the absence of actual data, your assumption that this is the bulk of bird deaths seems like obvious wishful thinking. It's also just as easy to imagine many of the deaths are juvenile / nesting birds too. And unlike rats, most birds can't repopulate so quickly.
I'm not here to tell you I know the absolute truth on the matter, but I can say definitively that your assertion of this fact extends beyond conclusive data. Cats decrease rat sightings, but urban rat populations are good at evading them [1, 2]. Where cats do prey on rats, it's usually juveniles with ultimately little effect on local populations [3, 4].
It's easy to imagine that a certain percentage of the birds cats are killing are ill or old. Yet in the absence of actual data, your assumption that this is the bulk of bird deaths seems like obvious wishful thinking. It's also just as easy to imagine many of the deaths are juvenile / nesting birds too. And unlike rats, most birds can't repopulate so quickly.
[1] https://www.frontiersin.org/articles/10.3389/fevo.2018.00146... [2] https://www.nytimes.com/2018/10/12/science/cats-v-rats-in-ne... [3] https://www.jstor.org/stable/1381025 [4] https://journals.plos.org/plosone/article?id=10.1371/journal...