Do cats scare away rats? Sometimes, yes. But do cats truly deter rats? Well... not so much. A new innovative study shows that cats really aren't really very good predators of rats, and using cats to control rat populations isn't a good strategy.
While cats may be the undisputed kings and queens of the internet, they weren't always this popular -- and in many parts of the world, they still aren't. Historically, the reason why cats and humans go so well together was a very practical one: cats keep mice (and other related species away). But in the case of rats, things might not be as clear.
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Cats vs rats
Rats are often vilified for their uncanny presence in our settlements. These rodents are intelligent, sociable, and adaptable -- and this makes them a fearsome pest. Rats also have few natural predators in city ecosystems. So unsurprisingly, many people thought cats can keep rats away.
Cats are the prototypical enemy of rodents. Mice are instinctively afraid of cats, and since mice and rats are both rodents, it seems to make sense that cats can also keep rats away. This idea is also backed by earlier research.
For instance, one study from 1953 found that in the English countryside, farms that have cats substantially reduced rat infestation.
"Four out of five farms and a cottage on a downland area in Berkshire, on which cats were installed, remained almost completely free from rats after the latter had in at least three cases been initially destroyed by other means. The other farm, that had no cat, suffered recurrent infestation. Ricks more than about 50 yd. from cat-occupied units continued to have rat infestations, often heavy ones," wrote C.S. Elton from the Bureau of Animal Population in Oxford, UK.
The study noted that cats are better at keeping a clean house rat-free rather than cleaning an infested area.
"From these and certain other instances, it is concluded that if a sufficient number of cats (say, four) is introduced after complete rat extermination has been done, and if part of their food is supplied as milk, they will maintain the immediate area of the farm buildings rat-free. They will not necessarily clear a farm of an existing rat infestation."
It's important to keep in mind that this is a study from the 1950s. In fact, data on whether cats keep rats away is surprisingly scarce and often restricted to studies that are several decades old. In, fact, the above-mentioned study makes a rather bizarre mention that "the quantity of cats if probably more important than their quality."
So what does more recent research say about cats versus rats?
Cats scare rats away -- sometimes
The idea isn't that cats scare rats away by individually hunting them. Granted, in a 1 v 1 combat, a cat is far superior to a rat and can almost always kill the rat. Rats are woefully unprepared for the fight, while cats are supreme killing machines. They say that a desperate rat is capable of anything, and that may be true -- but even when the two are comparable in size, if the cat wants to kill the rat, it can almost always do so.
But the reason why cats can keep rats away doesn't have anything to do with fighting at all -- but rather, with avoidance. Simply speaking, rats are afraid of cats and avoid cats.
"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," says the study's lead researcher Dr. Michael H. Parsons, a visiting scholar at Fordham University. "This raises questions about whether releasing cats in the city to control rats is worth the risks cats pose to wildlife."
"New Yorkers often boast their rats 'aren't afraid of anything' and are the 'size of a cat'," Parsons adds. "Yet cats are commonly released to control this relatively large, defensive and potentially dangerous prey."
Parsons, an expert in urban biology, took advantage of a favorable situation. Along with his colleagues, Parsons looked at a specific situation in New York City: an instance when feral cats invaded a New York City waste recycling center, which also hosted a hefty population of rats.
Do cats keep rats away? This was the perfect instance to study this in a feral population.
The researchers monitored the behavior and movement of microchipped rats in the presence of cats, and they also set up motion-capture video cameras to quantify the effect of the cats on the rats.
It's the first time this has been studied in such a setting.
"We wanted to know whether the number of cats present would influence the number of rats observed, and vice versa," says Parsons. "We were also interested whether the presence of cats had any effect on eight common rat behaviors or their direction of movement."
Cats deter rats but they don't kill them
With a feral feline colony and a feral rat colony, you'd expect a lot of blood to flow, right? Well as it turns out, that's not the case. Over 79 days, cats killed just two rats. They usually went for easier prey.
Overall, researchers analyzed 306 videos taken over the study period. Although a few cats were always active around the rat colony, the researchers recorded just 20 stalking events, three kill attempts, and two successful kills. The two kills were when cats found rats in hiding and took them by surprise. The unsuccessful attempt was when during a chase -- a cat lost interest in the rat.
But rats did take notice of the cats. In fact, cats deterred the mice from going out as much as they did.
The mere presence of the cats dramatically shifted the behavior of the rats. Rats spent much less time in the open, and much more time 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," says Parsons. In contrast, the number of rats seen on a given day did not predict the number of cats seen on the following day.
"We already knew the average weight of the rats was 330 g, much more than a typical 15 g bird or 30 g mouse," says Parsons. "As such, we expected a low predation rate on the rats -- and our study confirmed this."
Cats can help, but they're not the best against rats
Ultimately, researchers say, it's not that cats can't kill rats, and even that they won't -- they absolutely can, and sometimes, will. It's just that the conditions need to be right, and the right conditions don't seem to happen that often. Furthermore, as Parsons underlined, using cats to keep rat populations under control seems like a flawed strategy that can easily backfire. Cats are also problematic for the environment, although they're much more agreeable to us humans.
Ultimately, while cats may not enjoy killing rats that much, they sure do enjoy killing all sorts of other wildlife, and the risks severely outweigh the advantages. In urban areas, cats are not the best population control for rats.
No doubt, we'll continue to struggle to contain rat populations in cities. These nocturnal creatures have evolved over millennia to become keen problem solvers, agile navigators, and skilled survivors in the face of adversity. Ironically, these are all traits we appreciate in humans. It's these very abilities, however, that have underscored their threat to human cities.
Journal Reference: Michael H. Parsons, Peter B. Banks, Michael A. Deutsch, Jason Munshi-South. Temporal and Space-Use Changes by Rats in Response to Predation by Feral Cats in an Urban Ecosystem. Frontiers in Ecology and Evolution, 2018; 6 DOI: 10.3389/fevo.2018.00146