Dynamic ecosystems need predators, but this isn't an argument in favor of letting pets roam outdoors - it's an argument in favor of not hunting, trapping or otherwise killing foxes, true wild cats, and coyotes. Moving up the ladder into mountain lions, wolves and grizzly bears does fill people with rising alarm (while there is an active movement to protect mountain lions and re-introduce wolves to California, I have yet to see any 'bring back the Grizzly' proposals, even though it's on the state flag - and mountain lions are enough to keep deer populations in check).<p>From an ecosystem perspective, cats are very successful hunters (the record for % of hunts that end in success is held by a small African wild cat^), but if there's a healthy coyote population in the vicinity, feral cats quickly become scarce (as do any overly fat squirrels).<p>^ <a href="https://youtu.be/nl8o9PsJPAQ" rel="nofollow">https://youtu.be/nl8o9PsJPAQ</a><p>Crows and ravens predate on baby birds and nestlings, but again this is a dynamic ecosystem norm. A backyard birdfeeder for songbirds tends to draw bird-hunting hawks too, which is fine, they're incredibly acrobatic and watching them hunt is quite the show - plus, natural (unsubsidized) predation removes the chaff from the wheat, improving the songbird population genetics. Young hawks in turn may be hunted by owls.<p>That's nature for you - and an argument for not letting pets roam outdoors unsupervised. Additionally, letting cats eat wild animals tends to lead to internal parasites, fleas, viruses etc.