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The first study to document interactions between wild cats and a colony of wild rats reveals that, contrary to popular belief, cats are not good predators of rats. In an innovative approach, researchers monitored the behavior and movement of electronic chip rats in the presence of cats living in the same area. They show that rats actively avoided cats and that only two rats were killed in 79 days. Published as part of a special issue on rodents Borders in ecology and evolution, the results provide more and more evidence that the threat they pose to birds and other urban wild animals outweighs the benefits of using cats to control rats.
"Like any prey, rats overestimate the risk of predation – in the presence of cats, they adjust their behavior to become less apparent and spend more time in burrows," says lead researcher Dr. Michael H. Parsons. at Fordham University. "This raises questions as to whether the release of cats in the city to control rats is worth the risk that cats pose for wildlife."
People have long associated cats with the natural enemy of rats. However, Australian and American researchers say that cats prefer smaller, defenseless prey such as birds and smaller wildlife, making cat a threat to urban ecosystems.
"New Yorkers often boast that their rats are" scared of nothing "and are the" size of a cat, "says Parsons." Still, cats are usually released to control this prey relatively large, defensive and potentially dangerous. "
"So far, no one has provided reliable data on the number of cats killed in the city," adds co-author Michael A. Deutsch of Arrow Exterminating Company Inc. "But the data is very clear about the effect of cats on native wildlife. "
When wildcats invaded a waste recycling center in New York City, the researchers took the opportunity to correct the problem. Their team was already studying a colony of more than 100 rats living inside the center, microchipping and releasing the animals to study their history. When the cats entered the search area, they installed motion capture video cameras to quantify the effect of cats on rats – the first time this was studied in a natural setting.
"We wanted to know if the number of cats present would influence the number of rats observed, and vice versa," says Parsons. "We were also interested in whether the presence of cats had an effect on eight common rat behaviors or on their direction of movement."
The researchers examined 306 videos taken for 79 days. Although nearly three cats were active next to the rat colony each day, only 20 harassment events, three attempted murders and two successful victories were recorded at that time. The two killings occurred when cats found rats secretly; the third attempt was an open chase where the cat had lost interest.
The videos also revealed that in the presence of cats, rats spent less time outdoors and spent more time in shelter.
"The presence of cats resulted in fewer observations of rats the same day or the next day, while the presence of humans did not affect rats' sightings," says Parsons. On the other hand, the number of rats seen on a given day did not make it possible to predict the number of cats observed the following day.
"We already knew that the average weight of rats was 330 g, much more than a typical 15 g bird or a 30 g mouse," says Parsons. "As such, we expected a low rate of predation on rats – and our study confirmed it."
"We do not say that cats will not get ahead of the city's rats, only these conditions must be met for this to happen," says Deutsch. "The cat must be hungry, have no other source of food less risky and usually needs an element of surprise."
The findings could explain why people continue to release cats as "natural" tools for controlling rats. "People see fewer rats and assume it's because cats have killed them – whereas it's actually due to the fact that rats are changing their behavior," Parsons explains.
"The results of our study suggest that the risks associated with the release of cats are largely outweighed by the risks to wildlife," he adds.
The research team plans to continue collecting data as part of their long-term study and will update their findings as new information becomes available.
"Although more research is needed to better understand the problem of city rats, we hope that our success will force others to carry out similar studies in other places," said Parsons.
But for now, in the battle of New York cats and rats, it seems like the rats are winning.
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