Feral cats appear to be pathetic at controlling New York City’s rats

People often assume cats enthusiastically kill city rats, but that may be just an urban legend.

Feral cats caught on video were keen to watch rats lurking around a trash collection center in Brooklyn, says behavioral ecologist Michael Parsons. But cats rarely killed, or even chased, the rats. Cats aren’t a good choice for rat-population control, Parsons, a visiting researcher at Fordham University in New York City, and colleagues suggest September 27 in Frontiers in Environment and Ecology.

Cats typically prefer smaller prey, he says. A 20-gram bird or a 30-gram mouse can’t defend itself with the sharp-toothed ferocity and heft of a Norway rat. Adult rats at the Brooklyn waste center are more than 10 times that weight, at an average of about 337 grams. For 79 days, cameras set up at the center showed cats killing or nearly killing only three rats. That lackluster performance wouldn’t do much to dent a rat population.

Parsons and his colleagues had been setting up a different rat study when they noticed five feral cats creeping around the rats that researchers had microchipped at the waste center. Researchers at first bristled at the intrusion, then realized it was a great opportunity to study feral animals in real-life situations, Parsons says. Trying to use lab rats to understand free-ranging rodents’ lives is like extrapolating “knowledge of the wolf from, say, a Chihuahua.”

The cats at the waste site paid attention to the rats, sometimes even sticking a feline nose into the hole in the wall that rats used as their home entrance. The rats also appeared to be warier, and the more cats that prowled the site on a given day, the less likely the rats were to be spotted, analysis showed. Such apparent disappearances might be why people believe cats help suppress rat populations. But in truth, the rats are probably still there. They’re just harder to see.

Actual cat attacks on the rats were rare. Out of 306 active-animal video clips collected, only 20 showed a cat stalking a rat. The rare kills occurred when cats had an advantage in pouncing on a rat trying to hide outside its home behind the walls.  One clip showed a partial and “very hesitant chase,” Parsons says, “like a stop-and-go dance they do. When the rat stops, the cat stops, too.”

Hungrier cats get more committed to rat chasing, and some people who release cats to control a rat problem withhold food to encourage hunting, Parsons says. But he argues that starving an animal to force it to confront less-favored and dangerous prey is “a horrible thing to do.”

The results of the study at the Brooklyn waste center go against popular opinion. But those results fit with earlier findings from alleys in Baltimore, where cats were similarly cagey around the bigger rodents. “Cats do occasionally catch rats, just not very often and not to the extent they reduce the size of the rat populations,” says disease ecologist Gregory Glass, who studied Baltimore rats but is now at the University of Florida in Gainesville.

Feral cats have other disadvantages, besides reluctant ratcatching.  Feral life is tough on the cats and increases perils for wild birds, says Susan Willson, a tropical avian ecologist at St. Lawrence University in Canton, N.Y.  Urban sprawls host more variety in bird species than many people realize, especially during migration seasons, and estimates for cat kills top a billion birds a year (SN: 2/23/13, p. 14).