U.S. wild bird losses to domestic, free-roaming cats may very well blow your mind. Scientific studies have estimated approximately 500 million birds in the U.S. alone are killed every year by both feline house pets and feral domestic cats. That's about 500,000,000 bird deaths per year.
Let's put that into perspective.
The human population of the U.S. is just over 300 million people as of 2010.
Or how about this...there are about 72 million pet dogs in the U.S. and about 82 million pet cats, for a total of about 154 million canine and feline pets currently (numbers of feral cats are unknown).
It's hard to say how many of these half a billion bird deaths are of introduced species such as starlings and some types of sparrow rather than our native birds (American Robins, warblers, Mourning Doves, etc.) - or how many are unfledged baby birds rather than adults. Perhaps the 0verall numbers are a bit lower as well - I've seen lower-end estimates put at about 300,000,000 bird deaths per year in the U.S. as a result of the tabby cat. In my mind, whether the real number is 250 million or 500 million per year, it doesn't matter. We still have a problem to face and issues to consider.
In comparison, wind turbines have been documented to kill less than 500,000 birds per year and as a nation we seem very worried about those losses. In fact I've seen this number used as reasoning against the use of wind turbines as alternative sources of electricity. Don't get me wrong, I want to see bird deaths from turbines minimized or eliminated as well, but my point is that we have an even bigger issue than wind turbines.
The ancient Egyptians were the first civilization to "domesticate" cats from a wild species in Africa so in no way are our pets "native" on this continent. Our domestic cats were brought to North America with the first European settlers just a few hundred years ago, so the native populations of wild birds have not had a chance to evolve to evade these very effective, silent predators.
Some might say "survival of the fittest." Perhaps, but are we mentally and emotionally prepared to lose many of the unique bird species that make this continent what it is? Or are we OK instead with it looking and feeling like Europe with only house sparrows and starlings at our feeders? Our native sparrows, finches, meadowlarks, buntings, warblers, wrens, robins, and wading birds (among others) have taken a huge hit from cats - are we OK with these losses?
If you think extinction can't possibly happen I'll say this one thing to you:
Remember the passenger pigeon?
I love cats, I really do. I love dogs too. But I love our native wild birds and mammals at least as much as I love domestic pets. With the kind of onslaught birds are having to contend with from our pets (and feral animals), our native wild birds don't stand a chance. When the wild birds are gone, they're gone. There is no getting them back. I know I am not prepared for a springtime with no bird songs, nor would I be thrilled with the loss of the variety of birds we have. I can't imagine going on a walk and seeing only starlings and European sparrows. I love seeing robins, warblers, thrushes, shorebirds, and so much more. The great variety of birds we have here on this continent is truly amazing - a gift from Nature. I'd like to give that same gift to the next several generations of Americans as well.
When I walk my dogs, I'm a responsible dog owner and keep my canines leashed so they don't scare other people or chase other animals. Please, do the same with your cats - keep them indoors or somehow under control. Don't let them roam (I can hear the objections already). Besides preventing them from killing birds and small mammals (and dropping them on your pillow as an offering), keeping your cats indoors prevents them from being run over by cars, eaten by coyotes, or poisoned by chemicals or rodent poisons.
Bells firmly attached to a cat's collar might be another option. There is conflicting evidence as to whether it really works to scare off birds but it may be worth a try.
If an indoor cat needs outdoor time and you have the space, you could build an outdoor enclosure for her - something similar to a large aviary, but to keep the cat in rather than a bird. Another option is to walk your cat on a leash. While walking a cat on a leash may sound silly I've seen this done many times. Yes, cats get used to it. One of my neighbors here in Maine does this a few times a day with her tabby. Granted, this isn't a fitness-excursion for the owner, but it gives her cat some quality time outdoors while keeping birds safe.
One other reason to keep your cat inside? Life expectancy. The average life expectancy of a pet outdoor cat is about 5 years. Indoor cats' average life expectancy is over 12 years.