Like a boomerang, relocated python comes back again

Burmese pythons need no GPS to find their way home. The enormous snakes that have invaded South Florida turn out to be determined and able navigators, with unexpected homing abilities.

Since at least 1995, Python molurus bivittatus snakes have been breeding in Everglades National Park, and for nearly as long, people have worried about how to get rid of them (SN: 2/25/12, p 5). The pythons can grow to be 5.5 meters long and robust enough to tangle with alligators and swallow the occasional adult deer. They also eat many small mammals including the endangered Key Largo woodrat.

In a study of how the pythons wriggle around the landscape, five of six adults that researchers captured and trucked 21 to 36 kilometers away managed to travel back to within five kilometers of their original locations, says Shannon Pittman of Davidson College in North Carolina. The snakes seemed highly motivated, spending about three to 10 months moving in an oriented way. They may even have a compasslike sense of a direction and a maplike sense of where they are, she and her colleagues propose March 19 in Biology Letters.

The snakes’ ability to navigate doesn’t bode well for efforts to contain them, Pittman says. Since the snakes seem to have a good sense of where they are, they may be able to take risks in exploring new habitat or venturing to far-off hunting areas.

Few studies have looked in detail at navigation in any snake. Sea kraits demonstrate homing powers, showing up in the waters of their native island in Fiji after researchers had moved them to another island about five kilometers away. But studies translocating timber rattlesnakes and Aruba rattlesnakes found the snakes wandering broadly, with no sign they were heading homeward.

To test python doings, Pittman and her colleagues caught 12 adults and drove them in covered containers to a wildlife center, where the researchers implanted radio transmitters under the snakes’ skin. Researchers then returned six of the snakes to their original capture spots and drove the other six to new patches where pythons are known to flourish.

Pythons slithered widely and the terrain was so difficult that researchers did much of their radio tracking with a small low-flying plane. The splotchy brown snakes are “secretive,” Pittman says. “You can be right beside a 10-foot snake and not see it.”

The translocated snakes moved faster and along straighter paths than the put-back-in-place snakes, the researchers found. Pittman now would like to know how younger snakes behave, because they’re the ones that move out in search of new homes.

How the snakes steered their course isn’t clear, Pittman says, though she notes that other reptiles can sense Earth’s magnetic field, solar cues, odors or polarized light. Pythons might rely on landmarks or familiar scents to tell when they’re home.

In the Everglades, the snakes don’t have to find a den for overwintering, so snake ecologist Howard Reinert of the College of New Jersey in Ewing finds it “a bit surprising” that pythons there would be so motivated to get back home. He’d like to know more about whether the nontranslocated snakes seemed particularly attached to their homes.