We've long been told that cats can help tamp down rat populations—let's face it, who wouldn't want a Ninja force of cats to combat vermin? However, a new study from Frontiers in Ecology and Evolution has shattered conventional wisdom, positing that cats actually don't catch that many rats.
Ecologist Michael Parsons, a visiting professor at Fordham University, spent time with colleagues observing the behavior of rats and cats at a rat-infested Brooklyn recycling facility. (Nice work if you can get it.) The study concludes that "feral cats (Felis catus) are predators that cause widespread loss of native wildlife in urban ecosystems. Despite these risks, cats are commonly released as control agents for city rats (Rattus spp.). Cats can influence their prey directly by killing or indirectly through changes to feeding or space-use. However, cats prefer defenseless prey, and there are no data suggesting that cats influence large (>300 g) urban rats."
In other words, cats don't really want to expend much energy chasing after and fighting with rats, which are more of a pain to catch and kill. Plus they are rats!
Parsons had actually been researching rat behavior when he made the discovery. According to Scientific American, this was his initial reaction to noticing the cats at the recycling facility: "As a behavioral ecologist, I was like, ‘Let’s get rid of the cats so we can do our rat research.'" But then he realized, "We don’t know what the rats will do around the cats," which quickly became, "Hey, let’s study what impact [the cats] have on the rats." From Scientific American:
“The cats didn’t really bother [doing anything] when the rats were on the open floor,” Parsons says. In one video, a rat walks calmly around the floor while a cat watches it from a box a few feet away...
Researchers did see some violent interactions, in which the cats actively chased the rats—but that was rare. In the hundreds of videos there were only three kills (“all ambushes,” according to Parsons) and 20 stalking events. The cats had no real effect on the rat population, Parsons says. “If you are paying [to feed] five cats to be around to control 150 rats, well, that’s not happening. Rats are still pouring out of the colony.”
While the team did find that rats were more cautious when cats were in the vicinity, disease ecologist Gregory Glass said, "Cats do occasionally catch rats, just not very often and not to the extent they reduce the size of the rat populations." WHO CARES as long as they look fierce (and cuddly) while guarding produce and newspapers.