Cats are ineffective at controlling city rat numbers

A new study has found that cats are not the answer to New York City’s rat problem. In the first investigation to document the interactions between feral cats and a colony of wild rats, researchers found that rats were skilled in dodging the cats, and only two kills were recorded in 79 days.

The research adds to a growing collection of evidence that the benefits of using cats to control city rats are outweighed by the threats posed to birds and other wildlife.

Study lead author Dr. Michael H. Parsons, a visiting scholar at Fordham University.

“Like any prey, rats overestimate the risks of predation. In the presence of cats, they adjust their behavior to make themselves less apparent and spend more time in burrows,” said Dr. Parsons. “This raises questions about whether releasing cats in the city to control rats is worth the risks cats pose to wildlife.”

Even though cats have been long perceived as the natural enemy of rats, some researchers have found that cats prefer smaller, defenseless prey such as birds.

“New Yorkers often boast their rats ‘aren’t afraid of anything’ and are the ‘size of a cat’,” said Dr. Parsons. “Yet cats are commonly released to control this relatively large, defensive and potentially dangerous prey.”

“Until now, no one has provided good data on the number of city rats killed by cats,” added study co-author Michael A. Deutsch from Arrow Exterminating Company Inc. “But the data have been very clear as to the effect of cats on native wildlife.”

The research team was already studying a colony of more than 100 rats living inside a recycling center when cats invaded. The experts set up motion-capture video cameras to investigate, which is the first time that the effect of cats on rats has been monitored in a natural setting.

“We wanted to know whether the number of cats present would influence the number of rats observed, and vice versa,” said Dr. Parsons. “We were also interested whether the presence of cats had any effect on eight common rat behaviors or their direction of movement.”

Among 306 videos taken over 79 days, only 20 stalking events, three kill attempts, and two successful kills were recorded. The videos also revealed that in the presence of cats, the rats spent less time in the open and more time in hiding.

“The presence of cats resulted in fewer rat sightings on the same or following day, while the presence of humans did not affect rat sightings,” said Dr. Parsons.

“We already knew the average weight of the rats was 330 g, much more than a typical 15 g bird or 30 g mouse. As such, we expected a low predation rate on the rats – and our study confirmed this.”

“We are not saying that cats will not predate city rats, only that conditions must be right for it to happen,” added Deutsch. “The cat must be hungry, have no alternative less-risky food source, and usually needs the element of surprise.”

The research team will continue collecting data and updating their findings as part of a long-term study.

“Much more research is needed to better understand the city rat problem, we hope our successes will compel others to perform similar studies in other venues,” said Dr. Parsons.

The research is published in the journal Frontiers in Ecology and Evolution.

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By Chrissy Sexton, Earth.com Staff Writer