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Study finds Everglades pythons like saltwater mangroves as much as freshwater marshes

A Burmese python swims in a saltwater mangrove swamp at Florida’s southern tip. The snakes mostly live in freshwater marshes.
A Burmese python swims in a saltwater mangrove swamp at Florida’s southern tip. The snakes mostly live in freshwater marshes.
Published Apr. 29, 2015

For five years, scientists tracked the 19 Burmese pythons around the Everglades, following their radio and GPS signals. They were hoping to learn where the invasive snakes prefer to live.

The answer is: pretty much everywhere. They live in the trees, and they live underground. They mostly thrive in freshwater marshes — but there was one that, to the scientists' surprise, found a home in the saltwater mangrove swamp at the Florida peninsula's southern tip and stuck around for quite a while.

"They're completely capable of living in the Gulf of Mexico mangroves for a year," said Kris Hart, a research ecologist with the U.S. Geological Survey and the lead author on a study released Tuesday. "He was just happy as a clam in that saltwater."

The study is an attempt to figure out where best to target efforts to eliminate the most famous invasive species in the country — and to get a glimpse of where the big snakes might go next, Hart said.

The scientists put tags on the pythons they had captured and released them as close to where they had been caught as they could. Then they tracked where the reptiles roamed.

For the most part, each of the pythons stayed in an area roughly 3 miles wide by 3 miles long. They seemed to prefer sloughs and coastal habitats, particularly tree islands — tropical hardwood hammocks where the roots have collected enough detritus to create an island slightly higher than the water level in the River of Grass.

But then there's that one that spent a year in Cape Sable hanging amid the mangroves. Most snakes are sensitive to saltwater, which once gave scientists some hope for containing the pythons to the Everglades. Now they know the big constrictors are just as comfortable hanging out by the gulf as any beach-bound Florida tourist.

Scientists have already seen evidence that the pythons can swim, too. A few years ago one scientist trying to track down what happened to an endangered rat species that had been bred in captivity and released in Key Largo discovered that the tracking signal for one rat was coming from inside a python that had apparently swum over from the mainland.

The one in Cape Sable shows how adaptable the pythons can be. "They can live in the freshwater environment and be fine," Hart said, "and they can live in the saltwater environment and be fine."

Florida is infested with more exotic species than any other state, with the roster ranging from feral hogs originally imported by Spanish conquistadors to giant African land snails smuggled in a few years ago by a religious cult. But the pythons have proven the most persistent and difficult to deal with.

Nobody knows how many pythons there might be in the Everglades. One estimate said there might be 150,000, but that number has been disputed by some experts. Pythons are ambush hunters, so adept at concealment that biologists have had a hard time spotting snakes that have been fitted with radio tags that give their exact position. That makes it difficult to do a census.

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What is clear is that pythons have largely taken over the southern half of Everglades National Park. Wherever the snakes go, scientists have reported finding a 99 percent decrease in raccoons, a 98 percent drop in opossums, a 94 percent drop in white-tailed deer and an 87 percent falloff for bobcats — and rabbits and foxes were gone entirely.

Generally the pythons in the study ate birds and mammals and even some alligators. The alligators fight back, though. In 2005 an Everglades National Park employee snapped photos of a python that had died while attempting to swallow an alligator. However, the people licensed by the state to hunt pythons have been told not to eat whatever they catch. The big snakes are full of mercury, a toxic chemical that may have been in the tissues of whatever the snakes ate.

State officials have tried everything they can think of to get rid of the pythons, including holding a monthlong python hunt outside the national park's boundaries. Most of the 1,500 hunters who signed up for the 2013 Python Challenge never saw a single snake. They killed 68 — fewer than the number of eggs typically laid by a female python — but the Florida Fish and Wildlife Conservation Commission announced this month that it's planning another hunt for 2016.

The extensive studies that have been done on the Everglades pythons, such as this one, Hart said, mean that "we know more about these guys here in Florida than we know about them in their native range."

Ironically, in Southeast Asia where the pythons come from, they are classified as a threatened species, in part because of the loss of habitat, and in part because they are hunted and killed for their skin and meat.

Contact Craig Pittman at Follow @craigtimes on Twitter.


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