By Natalie Angier, The New York Times, January 29, 2013
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 shocking new truth: cats are far deadlier than anyone 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
domestic cats in the United States — 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
native mammals like shrews, chipmunks and voles rather than introduced pests
like the Norway rat.
The estimated kill rates are two to four times higher than mortality
figures previously bandied about, and position the domestic cat as one of the
single greatest human-linked threats to wildlife in the nation. 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 Dr.
Marra, who performed the analysis with a 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.
The findings are the first serious estimate of just how much wildlife
America’s vast population of free-roaming domestic cats manages to kill 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 — superpredators 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 ultimately 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, not only have
cats been filmed preying on cardinals, frogs and field mice, they have also
been shown lapping up antifreeze and sewer sludge, dodging under moving cars
and sparring violently 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, the manager of the community cat programs
at the Washington Humane Society.
Yet the new study estimates that free-roaming pets account for only
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 may 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,” Dr. Fenwick
of the bird conservancy said. “It’s estimated that there are now more than 500
T.N.R. colonies in Austin alone.”
They are colonies of subsidized predators, he said, able to survive in
far greater concentrations than do wild carnivores by dint of their
people-pleasing appeal. “They’re not like coyotes, having to make their way in
the world,” he said.
Yet even fed cats are profoundly tuned to the hunt, and when they see
something flutter, they can’t help but move in for the kill. Dr. Fenwick argues
that far more effort should be put into animal adoption. “For the great
majority of healthy cats,” he said, “homes can be found.” Any outdoor colonies
that remain should be enclosed, he said. “Cats don’t need to wander hundred of
miles to be happy,” he said.
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