For all the adorable images of cats that play the piano, flush the toilet, mew melodiously and find their way back home over hundreds of miles, scientists have identified a new truth: Cats are far deadlier than anyone had realized.

In a report that scaled up local surveys and pilot studies to national dimensions, scientists from the Smithsonian Conservation Biology Institute and the Fish and Wildlife Service estimated that U.S. domestic cats — both the pet Fluffies that spend part of the day outdoors and the unnamed strays and ferals that never leave it — kill a median of 2.4 billion birds and 12.3 billion mammals a year, most of them little native guys such as shrews, chipmunks and voles.

The estimated kill rates are two to four times higher than mortality figures previously bandied about, positioning the domestic cat as one of the single greatest threats to wildlife. More birds and mammals die at the mouths of cats, the report said, than from automobile strikes, pesticides and poisons, collisions with skyscrapers and windmills, and other so-called anthropogenic causes.

Peter Marra of the Smithsonian Conservation Biology Institute, and an author of the report, said the mortality figures that emerge from the new model “are shockingly high.”

“When we ran the model, we didn’t know what to expect,” said Marra, who performed the analysis with his colleague, Scott R. Loss, and Tom Will of the Fish and Wildlife Service. “We were absolutely stunned by the results.”

The study appeared Tuesday in the journal Nature Communications.

CATS AND WILDLIFE

The findings are the first serious estimate of just how much wildlife the country’s vast population of free-roaming domestic cats kills each year.

“We’ve been discussing this problem of cats and wildlife for years and years, and now we finally have some good science to start nailing down the numbers,” said George H. Fenwick, the president and chief executive of the American Bird Conservancy. “This is a great leap forward over the quality of research we had before.”

In devising their mathematical model, the researchers systematically sifted through the existing scientific literature on cat-wildlife interactions, eliminated studies in which the sample size was too small or the results too extreme, and then extracted and standardized the findings from the 21 most rigorous studies. The results admittedly come with wide ranges and uncertainties.

Nevertheless, the new report is likely to fuel the sometimes vitriolic debate between environmentalists who see free-roaming domestic cats as an invasive species — super-predators whose numbers are growing globally even as the songbirds and many other animals the cats prey on are in decline — and animal welfare advocates who are appalled by the millions of unwanted cats (and dogs) euthanized in animal shelters each year.

All concur that pet cats should not be allowed to prowl around the neighborhood at will, any more than should a pet dog, horse or potbellied pig, and that cat owners who insist their felines “deserve” a bit of freedom are being irresponsible and not very cat friendly.

Through recent projects like Kitty Cams at the University of Georgia, in which cameras are attached to the collars of indoor-outdoor pet cats to track their activities, cats have been filmed preying on cardinals, frogs and field mice, and they’ve been shown lapping up antifreeze and sewer sludge, and sparring with much bigger dogs.

“We’ve put a lot of effort into trying to educate people that they should not let their cats outside, that it’s bad for the cats and can shorten the cats’ lives,” said Danielle Bays, a manager at the Washington Humane Society.

OUT WANDERING

The new study estimates that free-roaming pets account for about 29 percent of the birds and 11 percent of the mammals killed by domestic cats each year, and the real problem arises over how to manage the 80 million or so stray or feral cats that commit the bulk of the wildlife slaughter.

The Washington Humane Society and many other animal welfare organizations support the use of increasingly popular trap-neuter-return programs, in which unowned cats are caught, vaccinated, spayed and, if no home can be found for them, returned to the outdoor colony from which they came. Proponents see this approach as a humane alternative to large-scale euthanasia, and they insist that a colony of neutered cats can’t reproduce and thus will eventually disappear.

Conservationists say that, far from diminishing the population of unowned cats, trap and release programs might be making it worse, by encouraging people to abandon their pets to outdoor colonies that volunteers often keep lovingly fed.

“The number of free-roaming cats is definitively growing,” the bird conservancy’s Fenwick said. “It’s estimated that there are now more than 500 TNR colonies in Austin, Texas, alone.”