Using magnets to repel crocodiles - American crocodiles

Using magnets to repel crocodiles
Wed Feb 25, 2009 1:25pm EST
By Jane Sutton

MIAMI (Reuters) - Florida wildlife managers have launched an experiment to see if they can keep crocodiles from returning to residential neighborhoods by temporarily taping magnets to their heads to disrupt their "homing" ability.

Researchers at Mexico's Crocodile Museum in Chiapas reported in a biology newsletter they had some success with the method, using it to permanently relocate 20 of the reptiles since 2004.

"We said, 'Hey, we might as well give this a try," Lindsey Hord, the Florida Fish and Wildlife Conservation Commission's crocodile response coordinator, said on Tuesday.

Crocodiles are notoriously territorial and when biologists move them from urban areas to new homes in the wild, they often go right back to the place where they were captured, traveling up to 10 miles a week to get there.

Scientists believe they rely in part on the Earth's magnetic fields to navigate, and that taping magnets to both sides of their heads disorients them.

"They're just taped on temporarily," Hord said. "We just put the magnets on when they're captured and since they don't know where we take them, they're lost. The hope would be that they stay where we take them to."

Hord and his co-workers have tried it on two crocodiles since launching the experiment in January, affixing "a common old laboratory magnet" to both sides of the animals' heads. One got run over by a car and died, but the other has yet to return, Hord said.

Once an endangered species, American crocodiles' numbers have rebounded to nearly 2,000 in coastal south Florida, their only habitat in the continental United States. That puts them in increasing contact with humans, especially in areas where backyards border on canals around Miami and the Florida Keys.

Crocodiles are still classified as a threatened species, so game managers are reluctant to move them to new areas where they might be killed battling other resident crocodiles for turf rights, Hord said. Unlike alligators, which are far more numerous, each crocodile is considered important to preserving the species, he said.

"These crocodiles are unique and valuable creatures and we feel like we have a responsibility to live with these animals as much as we can," he said.

Many frightened residents don't share that view, although crocodiles are shy creatures, Hord said. Wildlife managers will try to relocate any thought to pose a significant risk, mainly those that seem to have lost their fear of humans.

Most crocodiles in Florida are tagged as hatchlings so biologists can easily recognize them, Hord said.

Any that come back twice after being captured and moved are sent to zoos or otherwise placed in captivity, something biologists hope to avoid if the magnet experiment works.

"This one is by no means a really well-developed scientific study with a control group. It's just something we thought we would try," Hord said. "We do have to make some room to live with them."

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