I've also seen way too many FIV+ cats come through the shelter system, transferred when they're attacked by FIV+ strays. If you ever need to give up your pet, FIV+ status is an immediate death sentence in many shelters. In no-kill shelters, it means a longer stay because some people are weirded out about "cat AIDS".
[1] http://planetbratfink.blogspot.com/2013/11/the-story-of-ange...
On a serious note: cats usually integrate well with their ecosystem and if they would really pose such a big threat, smaller mammals and brids would just migrate away. edit: I'm speaking of balanced ecosystems where cats have natural enemies, foxes and whatnot.
The majority of birds that cats kill are frail, in poor health, or otherwise likely to have not made it through the season anyway.
[1]:http://www.rspb.org.uk/makeahomeforwildlife/advice/gardening...
I doubt that those are all frail and doomed to an early death.
That's exactly what you don't want happening in an ecosystem.
Great suggestion.
But it's the complete opposite in the U.S, and although that makes sense in some places (a lot more predators in the countryside), in a city like San Francisco the risks seem identical to those of London. It's very strange. Of course, in the UK cat owners aren't legally liable for their cat's actions (cats, unlike dogs, are deemed by the law to be free agents), maybe that's not the case in the states.
Cats do kill wildlife, but their impact is often overstated. The RSPB (Royal Society for the Protection of Birds) in the UK has no issues with cats being let out, but recommend they have bells on their collars. The majority of birds that cats kill are sick, frail, or otherwise in poor health.
To quote the RSPB: "there is no scientific evidence that predation by cats in gardens is having any impact on bird populations UK-wide"[1].
[1]:http://www.rspb.org.uk/makeahomeforwildlife/advice/gardening...
(We've had a lot of "missing cat" signs on the group mailboxes lately. Woods nearby. Expanding populations of fishers, coyotes, wolves, etc. Did I mention I'm 15 minutes from Parliament Hill? Bears downtown, -35 C winters (with serious wind and a whole lotta snow), +35 C summers (with 90+% humidity), wild beasties in the woods.... I really love Ottawa. I mean, I must. No rationale person would live here otherwise.)
Cats do occasionally get run over, but most learn to avoid dogs and if they're getting second helpings of dinner at someone else's house, so what?