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When pythons take over Everglades, raccoons, rabbits and other small mammals vanish

University of Florida researchers hold a 15-foot Burmese python captured in Everglades National Park in 2009. The python had just eaten a 6-foot alligator.
Published Feb. 1, 2012


Pythons slither all over the southern end of Everglades National Park. And because of them, a new study says, a lot of animals that used to be seen in the Everglades are gone — apparently gobbled up by the invading snakes.


In a report published Monday, a team of scientists said they found that between 2003 and 2011, the areas where pythons had proliferated saw 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 that's not the worst of it.


"We observed no rabbits or foxes," the report noted.


The bottom line: "In areas where pythons have been established the longest … mammal populations appear to have been severely reduced."


The study, published in the Proceedings of the National Academy of Sciences, is the first to document the ecological impact of the pythons in the 1.5 million acre park.


It originated with scientists who were driving around in the park searching for pythons, said the study's lead author, Davidson College professor Michael Dorcas, who is also co-author of the book Invasive Pythons in the United States Ecology of an Introduced Predator.


The researchers collected their information by using systematic nighttime road surveys and counting both live and road-killed animals. In all, they drove 38,000 miles while crisscrossing the park over eight years.


There was a time when you couldn't drive 50 feet along one of the park roads without seeing a marsh rabbit ready to dive back into the bushes, said one of the co-authors, University of Florida professor Frank Mazzotti, who has been working in the park since the 1970s. And raccoons were once so numerous they became a major annoyance for campers, he said.


No more.


"After a few years, you start thinking, 'Hey, I haven't seen a raccoon in a while,' " Dorcas said.


When they checked, the scientists discovered the last report of a raccoon bothering campers in the southern part of the park was dated 2005.


Study co-author Robert Reed, a wildlife biologist with the U.S. Geological Survey, said the disappearance of rabbits raised serious questions about how widespread the pythons are.


"Because they breed like — well, like rabbits — they should be able to bounce back pretty well," from the pythons, Reed said. "The fact that they've been knocked back so far is pretty alarming."


Now when the scientists drive through the southern part of the park, "it looks the same, but the critters aren't there," Mazzotti said. "What makes the Everglades the Everglades is the critters that live there."


That's bad news not just for the River of Grass, he pointed out, but also for the predators that normally eat those mammals — black bears and Florida panthers, for instance.


To show the huge change, the scientists needed to compare the current situation to an Everglades before pythons were such a widespread menace.


Fortunately, Dorcas said, there were studies from the mid 1990s that documented how widespread the rabbits, foxes, bobcats, raccoons and other mammals had been. That way they could show a correlation between the rise of the pythons and the decline of the mammals.


Where the pythons didn't predominate, the small mammals were still plentiful, they found.


To Mazzotti, the study is similar to an indictment from a grand jury: "We assembled all the evidence, and there's enough evidence here to indict the Burmese python. But there's not enough to convict the Burmese python."


The scientists need to be sure that pythons, and not diseases or alterations in habitat or water flow, wiped out so many different mammal species, he said. Meanwhile Dorcas wants to study how the loss of those species could be affecting the rest of the River of Grass. There may be other species — wading birds, for instance, or alligators — where whatever role pythons may play in the decline is harder to detect, Dorcas said.


Take round-tailed muskrats, Reed of the USGS said. "We can't find them in the Everglades," he said. "The one place we do find them is in the pythons' stomachs. Even when we can't find them, the pythons can."


No one knows for sure how many pythons are slithering through the Everglades.


"It could be thousands, or tens or hundreds of thousands," Dorcas said.


So far nothing has stopped them — not hunters, not a severe cold snap, not even saltwater. Some pythons are showing up in the Keys, having apparently swum there from the mainland.


Earlier this month, Interior Secretary Ken Salazar banned Burmese pythons and three other species of exotic constrictors from being imported into the United States or carried across state lines. Salazar, in a statement, said the study "paints a stark picture of the real damage that Burmese pythons are causing to native wildlife and the Florida economy."


However, Mazzotti said the ban is slamming the barn door shut after the horse has bolted. "That will not help the current problem in Florida at all," he said.


Craig Pittman can be reached at craig@tampabay.com.

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