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Lure rats: a new conservation tool

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Idan Shapira with a lure rat cage used to attract
and trap wild rats in conservation areas.

Rats, the scourge of New Zealand’s conservation estate, are being lured and trapped by their own species in a novel approach to pest eradication developed by a Massey University biology researcher.

Idan Shapira, based at the Institute of Natural Sciences at Albany, says his experiments have tested the use of live caged lab rats in successfully attracting wild Norway rats (Rattus norvegicus) – the same species – when food bait fails to do the job.

The poison-free technique relies on the irresistible power of same-species attraction, with its promise of sex or social interaction, rather than food as a lure. Both the Department of Conservation and Auckland Council have already shown interest in using this method on protected conservation islands and reserves, as well as the Auckland Zoo.

Mr Shapira has been trialling the method for the past three years for his doctoral study on the role of olfactory attraction in invasive rodents as a tool for conservation. He says the method is particularly suited to conservation areas, such as islands, where re-invasion occurs following pest eradication through the use of poison. In these scenarios, one rat can cause significant devastation to vulnerable native birds and insects, and prove difficult to catch with traditional food bait because of the abundance of food available to them in the habitat.

“A single rat can cause a lot of damage. If it's a pregnant female it’s going to be even more of a concern,” he says. “This is a practical tool for conservation management in situations where you have a few rats to get rid of in protected wilderness areas,” he says.

Live lure rats have to be humanely cared for and fed, so it was not feasible to have a lot of them. They are held in a cage with two compartments; one for the lure rat and a separate area to trap the wild rat.

In his field experiments at Shakespear Regional Park north of Auckland, Matuku Reserve in the Waitakere Ranges in West Auckland, and on private land, Mr Shapiro caught a total of eight rats using food bait and more than 50 using lure rats.

In one trial he used infra-red cameras to capture the nocturnal activity around the cage. It shows three large rats keenly checking out the cage with the lure rat.

Auckland Zoo pest control coordinator Craig Knapp says the method has been a great success at the zoo, where rats were rejecting conventional baited traps because they find other food in the zoo. During a trial at the zoo, 11 rats were trapped using the lure rat. “That’s 11 rats we wouldn’t have caught using traditional traps,” he says. Rats can be a threat to smaller animals and birds at the zoo where poison is not advisable because of the risk of a poisoned rat being eaten by a zoo animal, he says.

Mr Shapira, who is part of Massey’s Ecology and Conservation Group, is in discussions with Hamilton Zoo about using the method there.

He says lure rats could potentially be used to detect and trap other small invasive mammals, such as stoats.

New Zealand has no native rats, but Norway rats (also known as brown or water rats) were on the ships of the first explorers who arrived here in the late 1700s. Ship rats (known as black or roof rats) came later on European ships. Between them, the two invasive species have eliminated several species of native birds and insects, and had a devastating effect on numerous others.


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