Costa Rica's "Problem Crocs" Return After Removal

Sharon Guynup
National Geographic Channel
September 26, 2003
Over a few weeks, a big American crocodile repeatedly lumbered into a village near Costa Rica's Tarcoles River and devoured some local dogs—not an unlikely occurrence in this region. Here, Pacific coastal development is bringing more people into crocodile territory—and tourists feed the crocs, helping them shed their natural fear of humans.

Unlike most countries, Costa Rica doesn't eradicate "problem crocs," but relocates them to less populated areas. But new tracking research suggests that for crocs, there's no place like home: 82 percent of displaced crocs returned, from as far as 62 miles (100 kilometers) away.

"As soon as you let them go, they seem to turn around and head home," said Perran Ross, a biologist at the Florida Museum of Natural History in Gainesville and coordinator of the Switzerland-based World Conservation Union's crocodile specialist group.

Brady Barr, a herpetologist and field specialist, and his colleagues trail and capture some of these "problem crocs," following their tracks to the river.

They often pursue these massive, aggressive males at night. From small boats, they shine bright spotlights across the water, searching for the unmistakable golden shine of crocodile eyes. When they locate the culprit, they temporarily blind the animal with the lights while Barr slips a metal snare over its head.

Relocating Crocs

Then they tow the animal to shore. It takes two or three men to subdue these 11 to 15 foot (3.5 to 4.5 meter) crocs, which weigh as much as 1,500 pounds (700 kilograms). They attach a radio transmitter to his tail, collect tissue samples for DNA analysis, blood for toxicology work, and take measurements.

"We gather as much data as possible because it's not easy to get your hands on a big croc," said Barr. "It's dangerous, not only for us, but for the crocs—but the payoff in terms of scientific data can be huge."

Then they tape the animals' jaws securely shut, load it into the back of a pickup truck—and drive it to another river some miles up or down the coastline.

Barr's primary reason for radio tagging 20 crocodiles over the last three years is to track them in their new environs.

Returning home after relocation is a risky, arduous journey. Crocs must swim downriver to the sea, where they encounter a maze of fishing trawlers with giant nets. Sometimes they must swim long distances in the open ocean—and during their entire voyage, they must avoid poachers.

This homing behavior has been documented in other parts of the globe. The Australians attempted to relocate some large saltwater crocodiles living near Darwin with the same results, said Ross. Problem American crocodiles in Florida were relocated at one time, but when it proved ineffective, wildlife managers changed tactics. Now they shoot them.

Navigation Skills

The big question is how they navigate. "The fact is, nobody knows," said Ross. "There have been no studies. But with animals like bees and pigeons that have been well-studied, one important element is personal knowledge of where they are."

"Problem crocs" are often 20 to 30 years old. Since crocs are wanderers by nature, over time, they may learn their way around a fairly large area. "Teenagers" disperse widely when they leave their mothers. Males move around in search of females, and females gravitate towards the coast to find nesting beaches. "I would speculate with some confidence that [crocs] know where they are," said Ross. But he adds that many organisms also use the Earth's magnetic field to orient themselves.

Others navigate via the sun, moon, and stars. Whether crocs use these celestial guides is unknown. "They see about as well as people, so they could visually locate the sun on the horizon or the moon," said Ross. They may use their sense of smell to navigate like sea turtles and other reptiles.

To pinpoint what the crocodiles do after relocation Barr is currently testing a new, cheaper tracking device that has been successfully used on lions in South Africa's Pilanesburg National Park—the first time they've been put on crocodiles.


This new technology marries the global positioning system (GPS) with cell phone technology. The transmitter is programmed so it calls a cell phone at prescribed intervals revealing an animals' location, which appears as a text message. If there are no cell towers nearby, it stores the data until the croc nears the next tower.

The new technology would be more efficient than radio tracking, which requires that someone physically track the animals on the ground. Crocs spend a lot of time in inaccessible places, says Barr: in mangrove labyrinths, underwater, and hunkered down in burrows for months at a time. "All we know is that they go from Point A to Point B, but we don't know what they're doing in between."

It is also a cheaper alternative to satellite transmitters, which are more effective than radio collars but cost a whopping U.S. $10,000 each; these new telephone transmitters cost U.S. $2,000.

"Obviously, there's a big difference between the behaviors of lions and crocodiles," said Barr. "But if this technology works, it will revolutionize the way scientists track crocs."

He'll test them on Nile crocodiles in South Africa, which are imperiled because changes to a local dam will raise water levels and swamp nesting beaches. Barr's team will try to track nesting females in order to help the government formulate a survival plan for the animals. If they're successful, they'll bring the cell transmitters to Costa Rica.

Managing Problem Crocs

Discovering the crocodiles' brilliant navigational skills is bad news because it means that relocation is not working.

One of the best alternatives says John Thorbjarnarson, a herpetologist at the Bronx-based Wildlife Conservation Society, is to educate the people living within crocodile habitat, teaching them basics, like not swimming or spear-fishing in croc-infested waters—and never feeding crocs. "Humans and crocs can get along quite well as long as there are clear limits," he said.

Barr and his colleagues are trying to formulate a new plan for Costa Rica's large, territorial male crocodiles. "It may mean starting a 'school for wayward crocs,' a breeding colony where hatchlings can be released back into the wild," said Barr.

"Hopefully, these new transmitters will help us answer many questions surrounding crocodiles, and help the scientific community come up with better management strategies that are good for both crocs and people," he said.

For more crocodile adventures watch our U.S. cable television program Reptile Wild with Dr. Brady Barr on Sundays at 7 and 7:30 p.m. ET / 4 and 4:30 p.m. PT.

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