Cats Kill Billions of Animals a Year
livescience.com
livescience.com
In the U.K. there is no scientific evidence to believe so. The birds that have suffered the worse population declines rarely interact with cats. Garden birds which you would expect pet cats to come into contact the most are the birds that are on the incline which would go counter to the argument that cats are killing them off.
The Royal Society for the Protection of birds [0] and the U.K. Government [1] do not lay the blame of decreasing bird populations on cats but more on humans changing how we farm food, remove hedgerow and other bird habitats [2].
Now is that the case world wide? No. In Australia feral cats are being blamed for damaging the native rodent population but that is feral cats, keeping your pet cat indoors won’t do much (if anything at all) to affect that number), iirc Australia’s government are not even calling to keep pet cats indoors. What they are doing though is culling the feral cat population. Which is just wildlife control at this point.
[0] https://www.rspb.org.uk/birds-and-wildlife/advice/gardening-...
[1] https://assets.publishing.service.gov.uk/government/uploads/...
[2] https://www.rspb.org.uk/birds-and-wildlife/advice/how-you-ca...