Research published this week finds that even newly-hatched pythons can survive in seawater for up to a month.
"The fact that this study has ruled out one of the most hoped-for forms of physical barriers, saltwater, as preventing the spread of invasive pythons in Florida puts even more onus on human action to prevent the spread of these damaging reptiles," U.S. Geological Survey Director Marcia McNutt said in a release. "This study demonstrates the distinct possibility that pythons could spread to new suitable habitats one estuary at a time."
Researchers with the U.S. Geological Survey tested the ability of 24 hatchling Burmese pythons that they had caught in the Everglades to survive given different types of water to drink. Some got fresh water, some brackish water (such as the slightly salty water found in mangrove swamps) and some full-strength seawater.
The hatchlings given brackish water survived an average five months but two lived more than 200 days. The hatchlings given only seawater survived on average one month, but one lived for 200 days, until the researchers ended the experiment. The paper is in the January edition of the Journal of Experimental Marine Biology and Ecology.
The research shows that open ocean, bays or shorelines aren't necessarily the protection against further python migration that state officials had hoped they would be.
The paper is the first rigorous scientific research to document what's been known anecdotally for some time: Burmese pythons don't mind taking a dip in the ocean. "A few weeks ago, one was seen swimming across Florida Bay," says Gordon Rodda, a research zoologist and expert on the snakes with the U.S. Geological Survey in Fort Collins, Colo.
While it's unlikely the snakes would swim "straight across the Gulf" to make it to Texas and Louisiana, Rodda could easily imagine them hopscotching up the coastline or between the islands in the lower Florida Keys.
"They might bypass a wildlife management area just by swimming around it. You can't just stick a big fence out into the Gulf of Mexico," he says.
Research has shown that snakes often prefer to swim rather than crawl because it uses less energy. One group of pythons that had been radio tagged in the Everglades stayed put for months until the water levels rose enough that they could swim and then they took off, Rodda says. "Swimming is a very efficient way to get around, and they will use it."
Burmese pythons are considered one of the largest snakes in the world and can grow up to 20 feet and 250 pounds.
They are native to Southeast Asia but were introduced to Florida via the trade in exotic pets. It's believed that some either escaped or were released, and formed breeding colonies beginning in the 1990s.
No one knows how many Burmese pythons there are in Florida. "That's the million-dollar question everyone wants answered," says Kristen Hart, lead author on the paper and a biologist with the U.S. Geological Survey in Davie, Fla. Some back-of-the-envelope calculations have come up with "tens of thousands," she says. There have been reductions in animals such as muskrats and marsh rabbits, and that might be because of the pythons, she says. "They eat everything from birds to mammals to alligators. If you were to design the perfect predator, it might be the python," Hart says.
The snakes kill their prey by asphyxiating them by constricting their ability to breathe while holding them in place with their teeth. Dead prey is swallowed whole. Last October, workers in the Everglades killed a 16-foot python that had just eaten a 76-pound deer.
The pythons are not considered a threat to humans, but have been known to eat dogs, cats and deer. Officials are especially concerned about endangered species, of which there are 31 in Florida whose size and behavior patterns make them vulnerable to the pythons
The pythons are known to have reached Key Largo, where there is evidence they're eating the endangered Key Largo wood rat, says Ken Warren of the South Florida office of the U.S. Fish and Wildlife Service. They've also been known to eat rare round-tailed muskrats.
While there have been sightings of pythons all the way down to Key West at the tip of the Keys, there's no evidence of established breeding populations in the Keys. "Obviously that's what we're trying to prevent," Warren says.
How the pythons got that far south isn't known, he says. "Whether they managed to get down there by swimming or crawling across a bridge or hitching a ride, we don't know," Warren says.