Burmese pythons have virtually wiped out raccoons, marsh rabbits, opossums and other once-common mammals in the southern region of Everglades National Park, according to a nine-year study that shows the snakes' devastating impact on the park's wildlife.
The study, Severe mammal declines coincide with proliferation of invasive Burmese pythons in Everglades National Park, was published Monday in the Proceedings of the National Academy of Sciences. The authors include scientists at Davidson College, the University of Florida, Virginia Tech University, Auburn University Denison University, State Museum of Pennsylvania, National Park Service and the U.S. Geological Survey.
To do the study, researchers conducted night-time surveys along roads from 2003 to 2011, looking for both live and road-killed animals. They compared their tallies with surveys from 1996 and 1997, before the snakes had become established in the park.
In the area where the snakes have been established the longest, the declines are severe: Raccoons down 99.3 percent, opossums down 98.9 percent, bobcats down 87.5 percent. Marsh rabbits, cottontail rabbits and foxes had completely disappeared.
The scientists the same surveys in similar but python-free areas north of the park and found normal concentrations of these mammals. In areas that pythons were just beginning to penetrate, they found reduced mammal numbers, although not as severe as in the areas where they had been established for years. The declines in the southern Everglades coincided with the arrival of Burmese pythons in the area. The authors ruled out competing causes such as disease or changes in habitat.
"This severe decline in mammals is of significant concern to the overall health of the Park's large and complex ecosystem," said Everglades National Park superintendent Dan Kimball in a written statement that accompanied the release of the study. "We will continue to enhance our efforts to control and manage the non-native python and to better understand the impacts on the Park. No incidents involving visitor safety and pythons have occurred in the Park. Encounters with pythons are very rare; that said visitors should be vigilant and report all python sightings to park rangers."
The Obama administration two weeks ago announced a ban on imports and interstate commerce in Burmese pythons and three other large constricting snakes. But that ban was delayed for years as the administration wrestled with the potential impact on jobs and the attendant political consequences, and it follows years of wide-open imports that allowed released or escaped pythons to establish themselves in the southern Florida wilderness.
No one knows how many Burmese pythons live in South Florida, although estimates commonly run into the tens of thousands. Over the past 12 years or so, 1,825 have been captured.
John Willson, a study co-author, scientist at Virginia Tech University and author of the book Invasive Pythons in the United States, said the python's impact on the park's ecosystem was clearly significant but required much more research to understand.
"The effects of declining mammal populations on the overall Everglades ecosystem, which extends well beyond the national park boundaries, are likely profound, but are probably complex and difficult to predict," he said in a news release. "Studies examining such effects are sorely needed to more fully understand the impacts pythons are having on one of our most unique and valued national parks."
The disappearance of raccoons was particularly dramatic, the study says, because they had been considered such a nuisance in the 1980s that the park had established an control program. Although they can still be found in coastal areas, the study says there have been no complaints of nuisance raccoons in the southern part of the park since 2005.
The impacts on some wildlife is unclear. The decline in foxes and bobcats, for example, could be the result of either direct killing by Burmese pythons or of the python killing these species' prey.
Linda Friar, spokeswoman for Everglades National Park, said the park will continue studying and trying to capture the snakes. In additional to park personal, 30 volunteers hold permits to capture them. Last year 169 Burmese pythons were captured in South Florida, down from 322 the previous year, likely due to a cold snap that killed a lot of them. She said the park is experimenting with eradication techniques and has a difficult time gauging their effectiveness on snakes that do a good job of hiding.
"They're evasive and they're difficult to find," she said.
Although the study looked at the impacts on common species, the authors said the results show a high risk to rare species such as the Florida panther. In its native habitat in southern Asia, the python has been known to kill leopards, so it could be well within its ability to take down a Florida panther.
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