MIAMI — For the first time, scientists have put numbers to the toll Burmese pythons have had on native wildlife in the Everglades.
But one word can sum it up: carnage.
In the decade since the giant constrictors started showing up in significant numbers, mammals once among the most common in Everglades National Park have declined dramatically, according to a study published online Monday in Proceedings of the National Academy of Science.
The study, based on night field surveys conducted over 10 years, found three animals had all but disappeared. Opossum sightings fell 98.9 percent. Raccoons — once so abundant park managers warned visitors to safeguard food from roaming groups of the wily thieves — dropped 99.3 percent. Marsh rabbits, brown bunnies frequently seen foraging along roads in the pre-python past, didn’t appear at all. Observations of bobcats, foxes and deer all also fell precipitously.
"We started this study saying, man, it appears we’re not seeing many mammals," said Michael Dorcas, a biology professor at Davidson College in North Carolina and the study’s lead author. "When we actually did the calculations, we were astonished by the magnitude of the declines."
The study suggests a near-collapse of mammal populations in the park and points to the python as prime suspect.
Frank Mazzotti, a wildlife ecology professor at the University of Florida, likened the study to a grand jury investigation — an important initial finding that shows mammal numbers shrinking at the same time the park’s python population was booming, rising from two captures in 2000 to 322 in 2010.
"We examined all the evidence and there is enough to indict pythons but we haven’t gone to trial yet," said Mazzotti, one of 11 university and federal government researchers who co-authored the peer-reviewed study.
He cautioned that research is needed to refine and confirm the impact of the snakes. Other factors, such as changes in Everglades water levels, could potentially have contributed to the mammal decline as well, he said.
Still, the study finds the link strong, noting little support for other causes of the mammal decline. There were no known diseases or significant environmental changes, such as losses of important habitat or shifts in water management regimes.
"Our data are consistent in any number of ways with python as the primary reason or maybe the only reason, either directly or indirectly," said Dorcas, author of the book "Invasive Pythons in the United States."
The Obama administration pointed to the findings as more justification for the decision earlier this month to ban the import and interstate sale of Burmese pythons, two types of African rock pythons and yellow anacondas.
"Pythons are wreaking havoc on one of America’s most beautiful, treasured and naturally bountiful ecosystems," said Marcia McNutt, director of the U.S. Geological Survey, whose scientists contributed to the study. "Right now, the only hope to halt further python invasion into new areas is swift, decisive and deliberate human action."
The study was based on 313 night-time surveys of main roads in Everglades National Park conducted between 2003 and 2011, as well as 26 surveys at sites along the park border and in adjacent federally protected lands. The declines were in comparison to similar surveys conducted in the park in 1996, before pythons were regularly captured in the park.
In the surveys, which covered a total of nearly 39,000 road miles, researchers counted both live and road-kill animals.
(c)2012 The Miami Herald
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