In areas where the pythons have established themselves, marsh rabbits and foxes can no longer be found. Sightings of raccoons are down 99.3%, opossums 98.9% and white-tailed deer 94.1%, according to a paper out Monday in the Proceedings of the National Academy of Sciences.
"What if the stock market had declined that much? Think of the adjectives you'd use for that," says Gordon Rodda, an invasive-species specialist with the U.S. Geological Survey (USGS) who published research in 2008 showing that Burmese pythons could conceivably expand across the southern portion of the United States.
"Pythons are wreaking havoc on one of America's most beautiful, treasured and naturally bountiful ecosystems," says USGS Director Marcia McNutt.
Burmese pythons are native to Southeast Asia, but accidental and deliberate release of snakes kept as pets in Florida have allowed them to find a new home there. They can grow up to 16 feet long and weigh up to 150 pounds. The first reports of Burmese pythons in the Florida Everglades began in the 1980s; a breeding population wasn't confirmed there until 2000.
Since then, the numbers of pythons sighted and captured in the Everglades have risen dramatically. According to Linda Friar with Everglades National Park, park personnel have captured or killed 1,825 pythons since 2000.
Now researchers have shown that just as python populations established themselves, the native mammals of the regions began to decline severely.
People working in the Everglades knew they were seeing fewer mammals, but only when the hard numbers came in was it clear just how devastating the decline has been.
"These were once very common animals in the Everglades, and now they're gone," says Michael Dorcas, a professor of biology at Davidson College in Davidson, N.C., and lead author on the paper.
The pythons aren't a danger to humans. The only known python attacks on humans in Florida have involved snakes kept as at-home pets, says Dorcas, who also authored a recent book, Invasive Pythons in the United States. Now coyotes and Florida panthers are believed to be affected, as well as birds and alligators.
The decrease in mammals is highest where python populations have been established longest, and more mammals are being sighted in areas where the pythons have only recently been documented.
Although scientists can't say conclusively that the decline is a result of python activity, there's good anecdotal evidence. "Last October, we found a 15-foot snake with an 80-pound doe inside it," Dorcas says.
The researchers base their findings on systematic nighttime road surveys done in the Everglades that counted both live and road-killed animals. Ten researchers traveled a total of nearly 39,000 miles from 2003 to 2011 and compared findings with similar surveys conducted in 1996 and 1997.
Mammals in Florida have no natural fear of large snakes because they haven't existed in the area for about 16 million years, when a boa-like snake that used to live there became extinct.
The loss of the mammals is devastating not only to those populations, but to all the animals that rely on them. It's possible that the decline in bobcats, foxes, coyotes and panthers is linked to the disappearance of their typical prey: rabbits, raccoons and opossums.
Pythons also are eating lots of birds. More than 25% of pythons found in the Everglades contain bird remains.
They also happily eat pets, including cats, dogs and some farm animals. Roosters and geese have been found in their stomachs.
And there's not much that can be done. These snakes are "notoriously hard to find and very secretive," Dorcas says. Because much of South Florida is a vast wilderness, the possibility of exterminating or even suppressing them doesn't seem promising, he says. "It's an ecological mess, and exactly what's going to happen down the road remains to be seen."
On Jan. 23, the U.S. Fish and Wildlife Service started the paperwork to ban the importation and interstate transportation of Burmese pythons, northern and southern African pythons and the yellow anaconda because they threaten the Everglades and other sensitive ecosystems.
These snakes are being listed as injurious species under the Lacey Act. Some reptile breeders and collectors, along with Republican lawmakers, argued the restriction constitutes job-killing red tape.
How far the snakes might expand their range is unknown. Research in 2008 showed they could possibly survive across the entire southern United States.
And research this month showed they could survive in saltwater, which had previously been believed to be a barrier to their expansion.
"All of Florida and much of the coastal plain of the southeastern United States is suitable habitat," Dorcas says.
