Rats! Feral cats fail at urban rodent control

All the feral cats (Felis catus) running free in New York City have some people thinking that at least these strays are helping control rat (Rattus spp.) populations. But despite all the pop culture references of cats preying on mice, do feral city cats really prey on these much larger rodents? Researchers say no.

In a study published in Frontiers in Ecology and Evolution, researchers set out to find out whether cats actually kill rats at a waste recycling center in Manhattan.

The study came about as sort of an accident. Researchers were studying how scents influence rat behavior. As they were microchipping and capturing videos of the animals to observe their behaviors, cats began showing up at the recycling center.

“We started asking the question of how can we get cats out of the site because they might interfere with rats,” said Michael Parsons, the lead author of the study and a visiting research scholar in the department of biological sciences at Fordham University. Then, they realized they could take advantage of the uninvited guests to quantify what happens between the two species.

After collecting information from motion capture video cameras placed at sites from the original scent study, Parsons and his colleagues examined over 300 videos taken over nearly 80 days. They found cats killed only three rats.

Up to three cats were present near the rat colony each day, they found, but there were only 20 stalking events where a cat would follow a rat. During the three successful kills, the cats were likely successful because they came at especially opportune times when they could corner and ambush the rats, Parsons said. On the open floor cats had no luck. To complete a kill, the team found, cats must be hungry, have no less-risky food sources available and have the element of surprise on their side.

The team also noticed rats changed their behavior and oftentimes sought shelter when the cats were around. Why? Because prey tends to overestimate risk, Parsons said. As a result, the presence of the cats did impact the rats’ behavior, researchers found.

“But on the other side we have to realize that cats had almost no impact on the population of the rats,” Parsons said. Meanwhile, feral cats can kill native species, resulting in a less healthy ecosystem, he said.

“Cats typically prefer smaller meals of defenseless prey when available,” Parsons said, which includes species like neotropical birds and lizards, which are important seed dispersers and insectivores.

“A green city is a healthy city I want to live in,” Parsons said. “Cats can harm the ecosystem by their preference for smaller prey.”

Read TWS’ position statement on the Effects of an Invasive Species: Domestic Cats.