Burmese pythons munch marsh rabbits in Everglades National Park faster than any native predator, confirming what biologists already suspected: The invasive snake is changing the balance of the park’s food chain.
Two years ago, researchers determined that as the python population climbed in the park, the number of small mammals declined. But they couldn’t prove for sure that one caused the other.
A study published this week makes a stronger case for the connection, based on the fates of 26 rabbits fitted with tracking devices and let loose in the park in September 2012. The rabbits, which are native to the park but have nearly vanished in the last decade, did well. They settled in, started breeding like bunnies and seemed to thrive, said University of Florida biologist Robert McCleery, one of the study’s authors.
Then, as temperatures climbed, the rabbits started to disappear. Where? Inside pythons.
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Stoked by the hot weather, pythons started gobbling up rabbits faster than scientists expected — and even faster than the rabbits could reproduce.
“None of us would have predicted that 77 percent of the rabbits would be eaten by pythons,” McCleery said.
While McCleery is careful not to say the results indicate pythons are behind all other small animal declines in the park, “we’d like to think we’re setting the stage to make it clear that this is a problem.”
Biologists chose the rabbits as a proxy for all small mammals because they are generally resilient to predators, he said. Pythons also don’t restrict their diets, so the rate of rabbit consumption could reflect other mammals.
After the 2012 findings, the debate over the snakes’ impact on the park heated up. Some scientists worried the findings were too indirect and suggested one of the many other threats to the imperiled ecosystem, like changing water levels, could be driving away small animals.
“We saw a 90 to 95 percent decline in raccoons and possums,” said United States Geological Survey biologist Brian Falk. “That made people think, uh-oh, pythons are eating their way through the park.”
Working off the hypothesis of “what would happen if we could get rabbits and put them in Everglades National Park,” the scientists started trapping marsh rabbits in stormwater treatment areas outside the park, strapping on trackers and releasing them inside the park. Every two days, the team tracked down the rabbits to check their conditions. If the rabbits stopped moving for six hours, sensors alerted scientists.
In 16 of the 17 rabbit deaths, scientists found irrefutable proof of the connection: Trackers led scientists directly to snakes. The 17th rabbit had been regurgitated and was covered with DNA from a python, McCleery said.
How the findings could aid in managing the snakes is not clear.
“We don’t know,” Falk said. “One thing they could do is they could start eating other things more. And we know they eat a bunch of birds, mammals, alligators. Forty-plus prey.”