Domesticated cats that roam outside kill vast numbers of birds and mammals. Over a couple of days during Thanksgiving in Bradford, Massachusetts, one of the locals presented, in that feline way, an inadvertent survey of rarely-seen mammals. Above is the head of something rodenty; the viscera were left as well. The rest of these were whole body corpses:
Meadow vole, Microtus pennsylvanicus.
Flying squirrel, Glaucomys volans. 
One of two side-by-side White-footed mice, Peromyscus leucopus.
The cat also snagged a Dark-eyed junco. A mole scurrying towards the cat almost joined the tally, but this was one incident I actually saw. My intervention was a surprisingly effective pointed finger at the cat, but that was, I’m sure, only temporary. The mole, meanwhile, disappeared into the leaves.
Bring your cats inside — it’s safer for them, too. Here’s the American Bird Conservancy’s Cats Indoors Program for more information.
Backyard and Beyond 
This is not a scientific survey, and these critters have plenty of other natural predators as well. The other predators just don’t bring their prey to you.
The issue is not nearly as grave as the “roaming housecats are decimating wildlife!” camp insists.
And please don’t post that single, terribly flawed survey done years ago in WI or MI.
Of course it’s not a scientific survey, but then you don’t sound like somebody who would be convinced of one of those anyway. Obviously other predators kill to survive. This cat ate only one of its five kills (status of junco unknown). Most of those other predators are native to the ecosystem. Outdoor and feral cats are not, and number in the tens of millions, putting unnatural strain on nature. Additionally, every vet I’ve ever met agrees that domestic cats shouldn’t be allowed to roam outdoors for their own health. Audubon and other not-cat-centric conservation organizations in the country thinks that TNR — trap neuter and return — is a disaster for wildlife. In my own experience on an island, the local ring- necked pheasants (admittedly not a native species) were eradicated by cats, one of them my own family’s when I was young. The evidence was piled on the back porch. One can be a cat lover — Mavis fur ball slept snuggled against my chest last night — without excluding the rest of the planet.
As a cat lover an owner of a feline rooftop roamer, I can’t argue that cats kill. They do, and devastatingly. Mine retricts himself to cicadas as his environment is not very bird friendly. My parents in Cape Town have not acquired new cats since the last of their indoor/outdoor brood wandered off into that good night and now their garden is alive with birds, both rare and common.