Wildlife biologists have largely tracked the invasion of the recondite Burmese python in South Florida by what they didn't see: marsh rabbits, wading birds and other critters that have been voraciously consumed by pythons since the snakes arrived in the Everglades over three decades ago.
But a new study published Tuesday by the U.S. Geological Survey offers to change that with five years of tracking data, the largest trove yet.
Using radio tags and GPS to monitor the activities of the stealth invader, scientists tracked 19 snakes for a collective 5,119 days to get a glimpse of where the snakes go to eat, mate and hide from inhospitable weather. It turns out that pythons in the Everglades inhabit far greater ranges than in their native Southeast Asia and make longer daily treks. And unlike their solitary cousins, Everglades snakes may hang out together.
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“It has to do with food and sex,” said the study’s lead author, USGS research ecologist Kristen Hart.
The findings, she said, could help better control the python explosion that has been blamed for upsetting the balance of the fragile wetlands. Biologists believe that the pythons are behind an alarming decline in small mammals and that they could put endangered species such as wood storks and Cape Sable seaside sparrows in even more peril.
“It gives us a sense of what could be impacted,” Hart said.
Pythons first appeared in the Everglades in 1979 but did not establish themselves until 2000. Some speculate that the infestation began after Hurricane Andrew smashed into a makeshift breeding facility in 1992. In the years since, the snakes’ numbers have grown exponentially, to as many as an estimated 300,000. And wildlife managers futilely have struggled to contain them with traps, poisoned prey and even a so-called Judas snake designed to tip off hunters.
Most biologists now agree that python numbers are too high for the snake to ever be eradicated. No natural predators exist — even alligators can become a meal. So far the biggest threat appears to be cold weather. A 2010 cold snap wiped out many of the snakes. Hart said that her team lost nine of the 10 snakes it had been tracking.
The snakes also are incredibly hard to detect. They can grow to about 19 feet, but have what zoologists call cryptic coloration.
“They’re the color of mud and palm trees and detritus and leaves. And they’re quiet,” said Hart, who once encountered a 16-foot, 168-pound female in the Everglades. She said she heard the snake long before she saw it.
But if more can be understood about the snake’s behavior, wildlife managers might have a better shot at focusing limited resources in the 2,400-square-mile park.
“We have a good bit of information on how they function in captivity, but not in the wild,” said park spokeswoman Linda Friar. “Potentially this could inform how we develop our management strategy.”
In the study, published in the journal Animal Biotelemetry, researchers found that the pythons preferred sloughs and coastal areas, and almost always sought out ones with tree islands. While a study of large constrictors in Australia shows that snakes tend to be faithful to certain areas, even after they are moved, the tracking shows that Everglades pythons may be only seasonally faithful. They may also be more partial to the kind of habitat, not the specific location.
Researchers also found that female snakes had a slightly larger range than males, and that both sexes congregate around tree islands, contradicting findings in their native habitat in Southeast Asia, where they are considered solitary creatures. It could be that birds establishing rookeries and drawing other egg-eating mammals create a snake smorgasbord on the islands. The eating fest then may become a sex fest during breeding season, with even more randy snakes drawn to an Everglades’ version of Holiday Isle.
Part of the difficulty in conducting the study was the wilderness itself, Hart said. Researchers had to monitor radio-tracked snakes weekly, frequently locating the snakes by air before hunting them down on the ground. At most, the teams could monitor only about 10 snakes at a time, she said.
“Imagine it’s 100 degrees and you’re bushwhacking through the Everglades,” she said.
Over five years, they tracked more than 50 snakes captured along roads. Teams surgically implanted tags in the snakes, which were observed for 24 hours before being released within 10 feet of where they were captured. They then tracked the snakes over the life of the battery, or re-implanted tags. Four snakes were found dead. In the end, Hart said, 19 snakes provided data to track, a large enough group for scientists to generalize about their behavior.
For ongoing research, the team will focus on GPS devices that will allow researchers to study the snakes remotely and focus on finding breeding females or smaller snakes that may be moving about even more rapidly.
But even if biologists become better at locating the snakes, Friar said the best offense is never having to craft a defense.
“We need to get the message out: Don’t let it loose,” she said. “There’s no going back on this one. So what’s the next one? Have we learned anything and can we prevent another species from affecting this pristine ecosystem?”