January 31, 2012
Burmese Pythons Taking Over The Everglades
It has been 12 years since the first reports of giant Burmese pythons invading the Everglades came pouring in, something that most people made light of back in the day. But now, scientists have taken measurements of the real impact this voracious species has made on the local ecosystem and the news is quite troubling.
In areas where the invasive pythons have established themselves, marsh rabbits and foxes can no longer be found. Raccoon sightings are down 99 percent, and opossums and white-tailed deer are few and far between, according to findings reported in Monday´s edition of the Proceedings of the National Academy of Sciences (PNAS).
Scientists say the “severe declines” in the population of small and mid-sized native mammals in the 1.5-million-acre national park are linked almost completely to the growing presence of Burmese pythons, many of which are escaped or abandoned pets.
This study is the first to document the ecological impact the Burmese python -- which can grow to more than 16 feet long -- has made on the wildlife of the Everglades.
Scientists say the pythons have become “an established invasive species” in the Everglades. They are considered an apex predator and will occasionally prey on the American alligator and the Florida panther. It´s impact has been dramatic on the region's smaller mammals, which have dropped sharply in recent years, say researchers.
For their study, researchers from Davidson College in North Carolina, along with funding from several other agencies, collected information by conducting nearly a decade of night-time road surveys inside the park and similar habitats outside it, where they counted both live animal sightings as well as road kill.
They also looked at records of road kill from previous surveys done by National Park Service rangers in the 1990s, before the pythons were common in the Everglades.
The researchers drove nearly 40,000 miles between 2003 and 2011 conducting more than 300 nights of observations.
What they found is: in areas outside the Everglades National Park small mammals are flourishing. But inside the park, not so much.
Before being recognized as an established species in 2000, intermittent sightings were reported for 20 years or so prior to that. The large snakes are now common across thousands of square miles in southern Florida. But while there are no exact estimates on how many there could be, some 400 specimens have been removed from the park by 2009 and has been steadily increasing year-on-year (except for a slight drop in 2010 due to a cold snap).
“Any snake population - you are only seeing a small fraction of the numbers that are actually out there,” said Professor Michael Dorcas, one of the study's authors, from Davidson College in North Carolina.
“They are a new top predator in Everglades National Park - one that shouldn´t be there,” he told BBC News. “We have documented pythons eating alligators, we have also documented alligators eating pythons. It depends on who is biggest during the encounter.”.
During the nearly 9-year long study researchers did not detect a single rabbit -- dead or alive. Nuisance calls involving raccoons used to light of the park service´s switchboard. But since 2005, not a single park visitor has called to report a nuisance raccoon, according to the study.
Water birds, including grebes, herons, and the endangered wood stork, also appear to be on the decline due to python predation, said the researchers.
Researchers are quite certain that the decline in so many animals coming from such different taxonomic groups are unlikely the cause of a disease outbreak or similar problem.
“The magnitudes of these declines underscores the apparent incredible density of pythons in the (Everglades) and justifies intensive investigation into how the addition of a novel apex predators affects overall ecosystem processes,” wrote the researchers.
Experts at the US Geological Survey (USGS), which co-funded the study, said the odds of eradicating the pythons now that they have established themselves in the park are “very low.”
US Interior Secretary Ken Salazar earlier this month announced that the US was set to approve a ban on the import of Burmese pythons. The move, which would help stop abandonment or escape by pythons taken in as pets, comes about 30 years too late, according to some experts.
The ban on importing the Burmese python comes after five years of debate and lobbying in the US capital. Florida´s Democratic Senator Bill Nelson was among those who campaigned for a ban, unraveling the skin of a 16+-foot long python at a 2009 Senate hearing to make his point.
Reptile breeders, python enthusiasts and collectors disputed that the tropical snakes posed much risk beyond southern Florida and argued that any ban would harm a multi-million dollar industry.
Dorcas, who authored a recent book, Invasive Pythons in the United States, said people should not worry about pythons in general. They are not a danger to humans, he noted. The only known python attacks on humans in Florida have involved snakes kept as pets.
Dorcas said that mammals in Florida have no natural fear of large snakes because they haven´t existed there for about 16 million years, when the last large snake became extinct there. The decline in smaller mammals will have a larger impact on animal higher up the food chain. A decline in rabbits, raccoons and opossums will have an impact on numbers of foxes, bobcats, coyotes and panthers that rely on them as food as well.
Besides smaller mammals, experts say the Burmese pythons have no problem feeding on other animals as well. These include housecats, dogs, farm animals, deer, and alligators.
Dorcas said more research is needed to assess the impact of such large declines. But, he added, “It´s not unreasonable to assume that any time we have major declines in mammals like this it´s going to have overall impacts on the ecosystem. Exactly what those are going to be, we don´t know. But it´s possible they could be fairly profound.”
Support for the research was also provided by Duke Energy, the J.E. and Marjorie B. Pittman Foundation, the Center for Forest Sustainability at Auburn University, and the National Park Service.
Image Caption: This large Burmese python, weighing 162 pounds and more than 15 feet long at the time of its capture in 2009, was caught alive in the Everglades and was found to have eaten an American alligator that measured about 6 feet in length. University of Florida researchers in the photo: Michael Rochford is holding the python's head, and Alex Wolf and Therese Walters are holding the python's body. Credit: Mike Rochford , University of Florida
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