Florida Tries Repelling Crocodiles with Magnets

The American crocodile used to be an endangered species, thanks to encroachment by humans on their natural territories. But in recent years they have recovered to where there are nearly 2,000 crocodiles in southern Florida, which is the only place they live in the continental United States. Unfortunately, southern Florida is becoming increasingly populated by humans, so the crocodiles are becoming more and more in contact with people, particularly in regions around Miami and the Florida Keys, where backyards are often bordered by canals.

Because crocodiles remain classified as a "threatened" species, Florida wildlife managers are reluctant to relocate captured crocodiles to any areas where they might end up dead from fighting for turf ownership with crocodiles already residing in those areas. Unlike alligators, each crocodile is important to keep them from resuming to their place on the endangered species list.

"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," says Lindsey Hord, the crocodile response coordinator for Florida’s Fish and Wildlife Conservation Commission. But many Floridians don’t share Hord’s view; although crocodiles are by nature shy animals, they are still too close for comfort for many people. As a result, when wildlife managers receive a report of a crocodile that appears to have lost its fear of humans, they pose a significant risk to people, so game officials will try to relocate them. Biologists in Florida try to capture and tag most crocodiles as hatchlings so they can be easily recognized when they reach adulthood.

Researchers based at the Crocodile Museum in Chiapas, Mexico, issued a report in a biology newsletter describing a method they had found to repel crocodiles from residential areas. They taped magnets to their heads temporarily to interfere with the croc’s "homing" instincts to return to familiar territory. Usually, when crocodiles are relocated from urban areas back to the wild, they turn around and go right back to the spot where they were captured. Some crocodiles have been known to travel up to 10 miles a week in order to get back. Biologists believe that they may rely on the Earth’s magnetic fields in order to navigate their way home. Because of this, taping magnets to their heads may disorient them enough to keep them from being able to find their way back. Mexican researchers have had some success using the strategy to permanently relocate about 20 crocodiles in the three years they have been using the procedure.

Hord’s team tried the method on two crocodiles since they first began the experiment in January, taping a common laboratory magnet on to the crocodiles’ heads. One of them was killed after being run over by a car, but the other one has not returned to the place where it was captured. The experiment will continue, but if any crocs come back after being captured twice at the same spot, they will be sent to zoos or nature parks, or otherwise located in captivity, but Hord and the other wardens hope the magnets work so the crocodiles can remain living in the wild.

When Hoy and other game managers read about the technique, they decided they might as well give it a try. "They’re just taped on temporarily," he 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."