(Reuters) - A slithering, surging population of Burmese pythons in the Florida Everglades, many of them escaped or abandoned pets, appears to be eating its way through many animals native to the sensitive wetlands, according to a new study.
Researchers writing in the Proceedings of the National Academy of Science found what they characterized as "severe declines" in the population of small and mid-sized native mammals in the 1.5 million-acre national park and linked it to the growing presence of Burmese pythons.
The study, the first to document the ecological effects of the invasive species on the Everglades, was released on Monday.
The giant constrictors, which commonly grow to be more than 16-feet long, are not native to the Everglades, the largest subtropical wilderness in the United States and home to a number of rare and endangered species.
But they are popular and legal pets in the United States. Some escape. Some are released by owners who panic as their baby
snakes quickly mature into giant, dangerous adults.
The pythons have been what scientists call "an established invasive species" in the Everglades, apex predators that occasionally prey on the American alligator and the Florida panther.
The python's impact has been dramatic on the population of smaller mammals, including raccoons, opossums, marsh and cottontail rabbits, foxes and bobcats, which have dropped precipitously in recent years, researchers said.
The researchers collected their information by conducting nearly a decade of night-time road surveys inside the park and in similar habitats outside it, where they counted both live animals sightings as well as road kill.
They also looked at records of road-killed mammals from previous surveys done by National Park Service rangers in the 1990s, before the pythons were common in the Everglades.
In all, the researchers drove nearly 40,000 miles between 2003 and 2011 and conducted more than 300 nights of observations.
Their findings: In areas outside the Everglades, where the pythons have not established themselves, small, furry creatures abound. Inside the park, not so much.
In fact, in southern end of the Everglades, where the pythons have been established the longest, researchers said raccoon sightings have dropped 99.3 percent, while sightings of opossum have dropped 98.9 percent and bobcat sightings have fallen 87.5 percent.
Researchers did not detect a single rabbit -- dead or alive -- once inside the park during the nine-year study. Nuisance calls involving raccoons used to light up the park service's switchboard, researchers said. Since 2005, not a single park visitor has called to report a nuisance raccoon, according to the study.
A number of water birds -- grebes, herons and the federally endangered wood stork -- also appear to be falling to python predation, the researchers said.
Because the animals that have disappeared over the past decade come from such different taxonomic and trophic groups, the researchers said it was unlikely a disease outbreak accounted for the decline.
"The magnitudes of these declines," the researchers wrote, "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."
The study did not focus on ways of reversing the python's impact on the Everglades. Experts at the U.S. Geological Survey, which helped pay for the study, said the odds of eradicating the pythons now that they have established themselves in the park are "very low."
Support for the research was also provided by Davidson College, Duke Energy, the J.E. and Marjorie B. Pittman Foundation, the Center for Forest Sustainability at Auburn University, and the National Park Service.
(Reporting by James Kelleher; Editing by Greg McCune)