Natural History

From the NY Times:

While public attention has focused on wind turbines as a menace to birds, a new study shows that a far greater threat may be posed by a more familiar antagonist: the pet house cat.

Nearly 80 percent of the birds were killed by predators, and cats were responsible for 47 percent of those deaths, according to the researchers, from the Smithsonian Institution and Towson University in Maryland. Death rates were particularly high in neighborhoods with large cat populations.

Predation was so serious in some areas that the catbirds could not replace their numbers for the next generation, according to the researchers, who affixed tiny radio transmitters to the birds to follow them. It is the first scientific study to calculate what fraction of bird deaths during the vulnerable fledgling stage can be attributed to cats.

“Cats are way up there in terms of threats to birds — they are a formidable force in driving out native species,” said Peter Marra of the Smithsonian Conservation Biology Institute, one of the authors of the study.

The American Bird Conservancy estimates that up to 500 million birds are killed each year by cats — about half by pets and half by feral felines. “I hope we can now stop minimizing and trivializing the impacts that outdoor cats have on the environment and start addressing the serious problem of cat predation,” said Darin Schroeder, the group’s vice president for conservation advocacy.

By contrast, 440,000 birds are killed by wind turbines each year, according to the United States Fish and Wildlife Service, although that number is expected to exceed one million by 2030 as the number of wind farms grows to meet increased demand.

The American Bird Conservancy generally supports the development of wind energy, but it argues that wind farms should be “bird smart” — for example, positioned so that they do not interfere with major migration paths or disturb breeding grounds, with their power lines buried to prevent collisions.

“I’m excited about wind; we just have to be careful where and how we put the turbines,” said Dr. Marra, who studies threats to birds, including from climate change and habitat loss. He said the leading cause of bird deaths over all, as opposed to the catbird fledglings in the study, remained collisions with buildings, windows and towers, followed by predators.

Yet wind turbines often provoke greater outrage than cats do, said Gavin Shire, vice president of the Bird Conservancy. “The idea of a man-made machine chopping a bird in half creates a visceral reaction,” he said, “while the idea of a predator with its prey in its mouth — well we’ve seen that on the Nature Channel. People’s reaction is that it is normal for cats to kill birds.”

Household cats were introduced in North America by European colonists; they are regarded as an invasive species and have few natural enemies to check their numbers. “They are like gypsy moths and kudzu — they cause major ecological disruption,” Dr. Marra said.

The difference between 500 million and 440,000 to eventually 1 million is not trivial.

I’m sure that if the eventual calculations of bird deaths are tabulated on wind energy that it will never approach the number of birds killed by cats.

But I could be wrong.

However, it is pretty clear that cats are not a trivial threat to bird populations.

They are also not natural predators and exist at much higher densities than any of the natural predators on this continent.

Not all cats are great killers, but many are. It just takes a tiny fraction of the huge domestic and feral cat population to cause massive consequences with bird populations.

This study was among suburban bird populations, and it strongly suggests that the much feted cat management strategy called TNR, which is often exercised in suburban or urban environments, is not an ecologically friendly endeavor.

Feral cats are like pollution. If someone or some firm introduced a pollutant into the environment that did to birds and small mammals and reptiles what cats do to them, we would want that person clapped in irons and that firm put out of business.

But because we think predation by feral and free-roaming domestic cats is just fine, we tolerate this nonsense.

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HT to Emily S  for passing this study along.