Image: Python
Michael R. Rochford  /  AP file
University of Florida researchers hold a 162-pound Burmese python captured in Everglades National Park, Fla. Therese Walters, left, Alex Wolf and Michael R. Rochford, right, are holding the 15-foot snake shortly after the python ate a six-foot American alligator in 2009.
By
updated 1/30/2012 4:53:30 PM ET 2012-01-30T21:53:30

A burgeoning population of huge pythons — many of them pets that were turned loose by their owners when they got too big — appears to be wiping out large numbers of raccoons, opossums, bobcats and other mammals in the Everglades, a study says.

The study, published Monday in the Proceedings of the National Academy of Sciences, found that sightings of medium-size mammals are down dramatically — as much as 99 percent, in some cases — in areas where pythons and other large, non-native constrictor snakes are known to be lurking.

Scientists fear the pythons could disrupt the food chain and upset the Everglades' environmental balance in ways difficult to predict.

"The effects of declining mammal populations on the overall Everglades ecosystem, which extends well beyond the national park boundaries, are likely profound," said John Willson, a research scientist at Virginia Tech University and co-author of the study.

Tens of thousands of Burmese pythons, which are native to Southeast Asia, are believed to be living in the Everglades, where they thrive in the warm, humid climate. While many were apparently released by their owners, others may have escaped from pet shops during Hurricane Andrew in 1992 and have been reproducing ever since.

Can swallow alligators
Burmese pythons can grow to be 26 feet long and more than 200 pounds, and they have been known to swallow animals as large as alligators. They and other constrictor snakes kill their prey by coiling around it and suffocating it.

The National Park Service has counted 1,825 Burmese pythons that have been caught in and around Everglades National Park since 2000. Among the largest so far was a 156-pound, 16.4-foot snake captured earlier this month.

For the study, researchers drove 39,000 miles along Everglades-area roads from 2003 through 2011, counting wildlife spotted along the way and comparing the results with surveys conducted on the same routes in 1996 and 1997.

The researchers found staggering declines in animal sightings: a drop of 99.3 percent among raccoons, 98.9 percent for opossums, 94.1 percent for white-tailed deer and 87.5 percent for bobcats. Along roads where python populations are believed to be smaller, declines were lower but still notable.

Rabbits and foxes, which were commonly spotted in 1996 and 1997, were not seen at all in the later counts. Researchers noted slight increases in coyotes, Florida panthers, rodents and other mammals, but discounted that finding because so few were spotted overall.

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"The magnitude of these declines underscores the apparent incredible density of pythons in Everglades National Park," said Michael Dorcas, a professor at Davidson College in North Carolina and lead author of the study.

Prime suspect
Although scientists cannot definitively say the pythons are killing off the mammals, the snakes are the prime suspect. The increase in pythons coincides with the mammals' decrease, and the decline appears to grow in magnitude with the size of the snakes' population in an area. A single disease appears unlikely to be the cause since several species were affected.

The report says the effect on the overall ecosystem is hard to predict. Declines among bobcats and foxes, which eat rabbits, could be linked to pythons' feasting on rabbits. On the flip side, declines among raccoons, which eat eggs, may help some turtles, crocodiles and birds.

Scientists point with concern to what happened in Guam, where the invasive brown tree snake has killed off birds, bats and lizards that pollinated trees and flowers and dispersed seeds. That has led to declines in native trees, fish-eating birds and certain plants.

In 2010, Florida banned private ownership of Burmese pythons. Earlier this month, U.S. Interior Secretary Ken Salazar announced a federal ban on the import of Burmese pythons and three other snakes.

Salazar said Monday that the study shows why such restrictions were needed.

"This study paints a stark picture of the real damage that Burmese pythons are causing to native wildlife and the Florida economy," he said.

Copyright 2012 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

Explainer: Ten of nature's scariest animals

  • Stephen Chernin  /  AP file

    Humans seem to love a good scare, particularly on Halloween. Ghosts, zombies, vampires and other fictional characters are good for putting a chill down your spine. But if you're looking for something truly scary, let nature be your guide. Click on the "Next" label to see 10 of the animal world's scariest creatures.

  • Box jellyfish pack a deadly sting

    Anders Garm

    The box jellyfish is ghostly and squishy, with 24 eyes and a tangle of tentacles, each equipped with about 5,000 stinging cells. The creatures pack a special type of venom — the most deadly in the animal kingdom — that is activated by contact with certain chemicals found in fish, shellfish and humans. The venom can cause cardiac arrest, cripple the nervous system, and eat away skin. Several victims stung at sea die before they reach shore.

  • Black mamba: Speedy snake with lethal venom

    Eric Marquette

    Even people who are fearless around snakes should be careful in the presence of a black mamba. Native to sub-Saharan Africa, the territorial and aggressive snakes grow up to 14 feet long and travel at speeds of more than 12 miles per hour. Fortunately, black mambas are shy and usually race away when humans approach. But when threatened, they attack with repeated strikes to deliver lethal venom. Only a quickly administered antidote saves victims from death. The black mamba gets its name from the color of the inside of its mouth, seen here.

  • Saltwater crocodiles eat people

    Greg Wood  /  AFP - Getty Images

    Saltwater crocodiles are aggressive and territorial. And unlike their North American alligator cousins, they regularly eat people. They live in saltwater estuaries, and freshwater rivers and swamps, ranging from Australia north to Southeast Asia. The biggest males weigh in excess of 2,200 pounds and measure 20 feet from toothy snout to scaly tail, making them the world's largest reptiles. Though they mostly dine on smaller prey such as fish and shorebirds, adults will occasionally tackle larger animals, including careless people. Tourists lure this croc out of the water with a chunk of meat.

  • Polar bears: a poster child best left alone

    USFWS

    Polar bears are a poster child for groups campaigning to save the world from the ravages of global warming. But the cute and cuddly image that polar bears project are an icy disguise. Polar bears are the world's largest land predators; some males top the scales at 1,500 pounds and wield 2-inch-long claws. They normally kill seals and the occasional walrus twice their size. Human attacks are extremely rare but potentially fatal.

  • Wolves are revered and feared

    AP file

    Revered by some, feared by others, the gray wolf is the world's biggest, most powerful dog. Strong jaws and sharp teeth help them rip into their prey. Wolves primarily hunt deer, moose and bison, but when wild supplies are tight, domestic cattle and sheep are easy targets — hence the wolf's uneasy relationship with humans. In the 20th century, the predators were nearly hunted to extinction. Continued fear of the wolf continues to muddy their road to recovery.

  • Lions take a mean bite

    Daniel Munoz  /  Reuters

    In 1898, a pair of lions reportedly ate 135 people working on a railroad in Kenya. Though lions continue to make the occasional human meal, most of the slaughtering now goes the other way. Today, the cats are vulnerable to extinction, due to their human predators. Conservationists are racing to keep the survivors alive. In this image, two lions at a Sydney zoo gaze at each other before a non-human meal.

  • Shark attacks: Very feared, very rare

    Image: Casa Rinconada
    Reuters

    Maybe the 1975 film "Jaws" is to blame, but whatever the cause, many humans are terrified of the great white shark, the largest predatory fish in the ocean. The fear is understandable: These giants have a mouth full of razor-sharp teeth, they can reach 20 feet in length, and they top the scales at 5,000 pounds. Despite all that, scientists insist the predators pose little risk to humans. They say the chances of winning the lottery are higher than the chance of being attacked by a great white. Moreover, most attacks are not fatal. In this image, a great white swims past a cage holding tourists.

  • Scariest spider is a recluse

    Image: Chankillo
    Justin Sullivan  /  Getty Images file

    Tarantulas give lots of people the creeps, but scientists say most of the big and hairy spiders are harmless to humans. The real spider to fear is the brown recluse, a six-eyed spider with a violin-shaped head and a venomous bite that can lead to necrosis — the death of skin tissue. Fortunately, as their name suggests, the spiders are reclusive and seldom aggressive, only biting when threatened. Most bites have little or no effect on their human victims, but some are nasty and even fatal.

  • Mosquitoes kill millions every year

    USDA

    The world's deadliest animal? The mosquito. In some parts of the world, these pesky, bloodsucking insects spread diseases such as malaria, dengue fever and West Nile Virus that kill nearly 3 million people a year. Many of the malaria deaths occur in sub-Saharan Africa, where scientists and international aid organizations are busy developing strategies to stop the disease's lethal spread.

  • Vampire bats feed on blood

    Ho  /  AFP - Getty Images

    Finally, what list of scary animals would be complete without the vampire bat? The thumb-sized flying mammals with eight-inch wingspans feed exclusively on blood in the dark of night. Their prime targets are cattle and horses, but they are known to attack humans, too. Heat sensors in the bat's nose help it find flowing blood. They bite through the skin with razor-sharp teeth and lap up what oozes out.

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