Invasive pythons are wiping out small mammal populations in Everglades

John “J.D.” Willson, a post-doctoral researcher in Virginia Tech’s College of Natural Resources and Environment, came to the university to study the effects of pollution on native reptiles and amphibians. Now, however, he’s getting national attention for his collaborative study on the environmental threat of an elusive, non-native snake proliferating in the swamps of southern Florida.

   

Researcher J.D. Willson holds a young Burmese python captured while basking on a canal bank in Florida's Everglades National Park. Researcher J.D. Willson holds a young Burmese python captured while basking on a canal bank in Florida's Everglades National Park.

The study, published in the Proceedings of the National Academy of Sciences, is the first to document the ecological impact of the invasive Burmese python and is setting off waves of alarm across Florida and neighboring states.

Burmese pythons are the likely cause of a dramatic mammal decline in Florida’s Everglades. Sightings of medium-size mammals are down as much as 99 percent in areas now inhabited by pythons. Willson’s research shows that the huge snakes — probably descended from escaped or released pets — appear to be wiping out raccoons, opossums, bobcats, and other mammals. Scientists fear for the environmental balance of the 1.5-million-acre Everglades National Park and surroundings areas.

“Such severe declines in easily seen mammals don’t bode well for the many species of conservation concern that are more difficult to monitor, particularly wading birds,” said Willson, co-author of the book “Invasive Pythons in the United States.”

“Our findings suggest that pythons are changing the Everglades ecosystem,” Willson added. “They are causing other wildlife to disappear, and that will have dramatic effects on the overall ecosystem.”

Concerned scientists only have to look at the example of the Pacific island of Guam to know where this could go. The invasive brown tree snake has killed off birds, bats, and lizards that pollinated the island’s trees and flowers and dispersed seeds. The snake’s presence led to the extinction of 80 percent of Guam’s native birds and huge declines in native trees and certain plants.

Tens of thousands of Burmese pythons, native to Southeast Asia, are believed to be living in the Everglades. In the wild, they can grow to 15 feet long and live more than 25 years. Although alligators may attack young pythons, the large adult snakes are likely at the top of the food chain. While birds make up more than a quarter of their diet, the snakes have been found with alligators and even deer in their stomachs. Some of the declining species could be both victims of being eaten by pythons and of having to compete with the pythons for food.

“Pythons are ambush predators,” Willson said. “They lie hidden in water and vegetation waiting for prey. They have an acute sense of smell and will eat a variety of warm-blooded animals, as well as alligators.”

   

Burmese pythons are often found crossing roads at night in Everglades National Park. Burmese pythons are often found crossing roads at night in Everglades National Park.

Pythons and other constrictor snakes kill their prey by coiling around it and suffocating it. Although Willson said he’s not in serious danger when he searches for pythons in the Everglades, he always hunts with a partner. “I have to be as careful around them as I would be around alligators,” he said.

At least 1,800 Burmese pythons have been caught in and around Everglades National Park since 2000. For this study, researchers drove 39,000 miles along Everglades-area roads from 2003 to 2011, counting wildlife and comparing the results with surveys conducted along the same routes in 1996 and 1997.

The researchers found staggering declines in animal sightings. They documented 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. Rabbits and foxes, commonly spotted in earlier years, were absent. Along roads where python populations are believed to be smaller, declines were lower but still notable.

   

Burmese pythons living in the wild can grow more than 15 feet long and live for 25 years. Photo courtesy of the U.S. Geological Survey. Burmese pythons living in the wild can grow more than 15 feet long and live for 25 years. Photo courtesy of the U.S. Geological Survey.

Officials must pick their battles with the pythons carefully, Willson said. “There’s no easy solution for controlling them, so we need to concentrate on sensitive areas, such as the heron rookeries and the Florida Keys. We’re refining our collection methods, but we don’t know how many pythons there are and there is no way to eradicate them completely at this point.”

“Non-native invasive species have become a problem worldwide,” Willson said. “Animals are getting introduced, whether it’s intentional or accidental. Although there are at least two other species of large constrictors taking up residence in South Florida, it’s the Burmese python that is causing the biggest problems.”

  • For more information on this topic, contact Lynn Davis or 540-231-6157.

Why have pythons spread?

The Burmese python earned its way to the top of Florida’s invasive species list just 11 years after being identified as an invasive species in the state. Burmese pythons have traits that have helped them become established quickly in southern Florida and make their eradication difficult. Specifically, Burmese pythons

  • Grow rapidly to a large size, 4 feet or more of growth in the first year
  • Can live in many kinds of habitats, from urban areas to the Everglades to the saltwater Keys
  • Can eat nearly any native mammal, bird, or alligator
  • Are difficult to detect because of infrequent movement between hiding places
  • Mature rapidly and produce many offspring
  • Achieve high population densities, share territory, and do not cannibalize their young

What to do with an unwanted python

Don’t release unwanted pythons into the wild.

“It’s best to contact a snake rescue agency or even euthanize your snake as a last resort. But don’t turn it loose,” said John “J.D.” Willson, a post-doctoral researcher in Virginia Tech’s College of Natural Resources and Environment.

Releasing a non-native constrictor snake is illegal in many areas, and a hungry, free-ranging python poses a serious threat to pets and wildlife. Some studies indicate pythons can survive in the southern third of the country, as far north as Washington, D.C.

“Whether they could actually live in Virginia year-round, I’m not sure,” Willson said. “But I have seen escaped pythons in the urban places I’ve lived, including Athens, Ga., and Charlotte, N.C.”

U.S. Interior Secretary Ken Salazar announced a federal ban on the import of Burmese pythons and three other snake species in January 2012. The Burmese python is also one of eight non-native reptiles listed as a conditional species, which may not be acquired as pets. People who owned a conditional species before July 1, 2010, may obtain a special license to keep their animal for the remainder of its life.

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