AP

A Burmese python is wrapped around an American alligator in Everglades National Park. Picture: AP/National Park Service, Lori Oberhofer

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 characterised 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 constrictors, which grow to be more than 5m, are not native to the Everglades, the largest subtropical wilderness in the US and home to a number of rare and endangered species.

But they are popular and legal pets in the US. Some escape. Some are released by owners who panic as their babies quickly mature into 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 smaller mammals, including racoons, opossums, marsh and cottontail rabbits, foxes and bobcats, which have dropped precipitously in recent years, researchers said.

The researchers conducted nearly a decade of night road surveys in the park and in similar habitats outside it, counting live animals and roadkill.

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 area.

Their findings: outside the Everglades, where the pythons have not established, small furry creatures abound. Inside the park, not so much.

In fact, in the southern end of the Everglades, where the pythons have been established the longest, raccoon sightings had dropped 99.3 percent, sightings of opossum dropped 98.9 percent and bobcat sightings had fallen 87.5 percent.

Researchers did not detect a single rabbit, dead or alive, in the park. Nuisance calls involving raccoons used to light up the park service’s switchboard, they said. Since 2005, not a park visitor had reported a nuisance raccoon.

A number of water birds – grebes, herons and the federally endangered wood stork – also appear to be falling to python predation.

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 was to blame.

“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 predator affects overall ecosystem processes.”

The study did not focus on ways of reversing the python’s effect on the Everglades.

Experts at the US Geological Survey, which helped pay for the study, said the odds of eradicating the pythons now that they were established in the park are very low. – Reuters