Science Matters: Solving the rat problem

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If your property is overrun with rats then you get a cat to deal with it, right?

Wrong, according to a recent study at an industrial waste recycling plant in Brooklyn, New York City.

This recycling plant hosts an active urban rat colony and the animals, numbering some 120-150, are unwitting research subjects for a group of environmental scientists interested in rat behaviours. The rats are microchipped and observed via field cameras.

So, when feral cats moved in next door, the scene was set to determine the efficiency of using cats as pest controllers. After all, while in some cities with huge rat problems cats are being released to control them, in other cities feral cats are being rounded up because of their detrimental effect on wildlife, particularly small birds.

The team found that when the cats visited the recycling plant fewer rats were seen on the cameras.  This gave the impression that the cats were eliminating rats, but actually the rats had just changed their behaviour, becoming more cautious and hiding away for long periods. In fact, during the five-month study scientists recorded 20 stalking events by cats but only two rat kills, so rat numbers were largely unaffected.

The scientists contend that cats only prey on rats if they are starving or if the rats are weakened in some way, and suggest that the two rats killed in their study could have been weakened by poisonous bait.

So despite cats being widely regarded as natural ratters, this is not the case. They prefer smaller prey such as mice, which are less calorific (mice weigh 20-35 grams while city rats are 10 time heavier) but are safer since rats have sharp teeth and can be vicious.

All in all the scientists conclude that the risks to wildlife posed by feline pest control outweigh any marginal benefits. However, they do concede that rural rats and island populations are appreciably smaller that their city cousins, and so may be more tempting to hungry felines.

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