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Wednesday, July 24, 2024

Florida’s War With Invasive Pythons Has a New Twist

While driving in the swamplands some 40 miles west of Miami, Mike Kirkland noticed a log lying in the road ahead, so he and his colleague stepped out of their white GMC work truck. This was no log. “As we got closer, we realized it was a python,” he says. “It was so big, it looked like a fallen tree.” Kirkland asked the colleague to hang back, then crept to within five feet of the predator as it basked on the warm pavement.

“She saw me,” he says. “I’m 5'11". And she picked herself up and practically looked me in the eye.” The snake’s sheer size gave him pause—but not for long. She stretched open her mouth, revealing dozens of curved teeth as sharp as daggers, then launched her head at Kirkland. He dodged a couple of strikes before spotting an opening to grab the snake’s head. The nonvenomous 17-foot constrictor then tried to wrap herself around the sweating Kirkland, who slipped through coil after coil. About 20 minutes later, the exhausted snake gave in, and Kirkland euthanized the animal.

This is all in a day’s work for Kirkland, an invasive-animal biologist who manages the South Florida Water Management District’s Python Elimination Program. His team patrols roads like this one beside Big Cypress National Preserve looking for Burmese pythons, one of the world’s most unyielding invasive species. The team recently removed their 8,000th python.

Florida has a twisted relationship with the Burmese python. Americans imported nearly 100,000 of them from Southeast Asia between 1996 and 2006. (The US banned their import in 2012.) Many pet owners hadn’t realized that the snakes grow to 12 feet, on average, and they abandoned them. South Florida’s warm wetlands offer the perfect adoptive habitat. Their inconspicuous patterning conceals them in the already remote Everglades, which makes them hard to track. Ecologists peg their detectability at less than 1 percent. That means if there are 100 snakes in your survey area, you’d be lucky to spot just one.

The pythons officially established a self-sustaining population in the ecosystem in 2000, according to the US Geological Survey. Today, there are likely tens of thousands of them across South Florida, and the USGS believes the number will only increase as populations expand to new areas within the peninsula. (They’re not likely to spread to similar wetlands in Alabama and Louisiana, though, since they can’t survive the colder temperatures they’d have to migrate through to exit northern Florida.) According to the USGS report, eradication is “likely impossible.” And now, says Kirkland, “They are eating all of our native wildlife.”

Earlier this year, USGS scientists synthesized decades of research on python biology and potential control tools. They described 76 prey species found in the guts of pythons: mammals, birds, iguanas, and even alligators. “Our native wildlife is not used to a large snake predator of that size,” says Melissa Miller, an invasion ecologist with the University of Florida. “Something that large is not really on their radar.” Ecologists often describe an invasive predator’s prey as “naive,” since they haven’t co-evolved with the thing that now might kill them.

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That has created a problem. Around 2010, soon after meeting this big, new predator that could outcompete and eat them, South Florida’s mammal populations collapsed. Large and medium-size mammals have been scarce for almost a decade, leaving mostly smaller mammals, like rodents.

Some ecologists thought the pythons would become victims of their own success. “They were supposedly out of food,” says Paul Taillie, a wildlife ecologist at the University of North Carolina at Chapel Hill. But Taillie’s research has shown that pythons just switched to eating the smaller mammals instead, causing those populations to drop too. In 2021, Taillie reported disappointing proof that mammals were not bouncing back. “There’s exceedingly little sign of any mammal activity” in South Florida, he says.

The only resistant species has turned out to be black rats—but they’re also invasive. Black rats arrived in the Americas from Europe centuries ago onboard the ships of explorers and colonizers. They’re resistant because they reproduce a lot and don’t compete with the pythons or large mammals for food: They can scavenge carcasses and eat plants, insects, and scraps from humans. This is the reason they thrive all over the world.

So can anything curb the python’s takeover? First, there are teams like Kirkland’s, which employ contractors to track and capture the snakes year-round. Every capture and kill follows ethics guidelines and federal laws about transporting illegal pets. “They need to be respected as the beautiful living creatures that they are,” Kirkland says. “They’re here through no fault of their own.”

And for six of the past 10 years, Florida has tried to educate the public about invasive species and the folly of keeping pythons as pets, thanks to the Florida Python Challenge, a 10-day event for amateur python hunters, in partnership with the state’s wildlife agency. Participants catch the snakes, which they euthanize. This year, at least 840 participants registered for a shot at $17,500 in prizes. The tally for this year’s hunt hasn’t been released yet, but each of the last two hunts yielded over 200 captures. “It really does a lot to educate the public,” Kirkland says, “to teach about the importance of why you shouldn’t allow an invasive exotic pet to get out.”

But scientists also want to know if the nonhuman denizens of the Everglades are pushing back against the python—specifically, to see if pythons have their own “prey naivete.” Could other species be preying on young pythons?

To answer this question, in 2020 and 2021 a team of USGS researchers implanted 2- to 3-foot-long pythons with radio transmitters and released them back into Big Cypress National Preserve. The transmitters tracked movements down to a 3-meter radius, and each transmitter had a “mortality sensor” that was triggered if the animal hadn’t moved in 24 hours.

Nineteen young pythons died during the study period. Team members waded into the swamp to find out exactly where and how. They snooped for every sign imaginable: paw prints, fur, bite marks, scrapes, and scat. Dead snakes and transmitters turned up in soil, in trees, and underwater. The team brought any carcasses they could find back to the lab for necroscopies. Twelve of the 19 cases had enough evidence to point to a killer, according to results published earlier this year in a study titled Natives bite back.”

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They had expected some deaths, but not as many as they found, says Amy Yackel Adams, a USGS ecologist on the team. “We were quite surprised,” she says, “especially by predation of native Florida species.”

Native alligators and cottonmouth snakes killed eight of the 12, and mammals killed four. One native cotton rat killed a python while being attacked. That rat was actually larger than the young snake, making it a risky meal. (The team couldn’t say which mammals killed the other three pythons, but they’ve noted bobcats and coyotes in the area. It’s possible that these species or others, like birds, killed the other seven snakes—but the researchers couldn’t find enough evidence to rule out other possibilities, like starvation.) 

“It’s always nice to see native species getting the upper hand with Burmese pythons, as it’s often not the case,” Miller says. She’s experienced alligators and crocodiles killing pythons—and a 15-foot python eating a 6-foot gator. (Miller contributed to the USGS review, but not the “Natives bite back” study. Her lab measures each snake from the Florida Python Challenge in an impartial judging role.)

It’s not surprising that native animals would begin pushing back, says Taillie, who was not involved in either USGS study: “Prey populations of invasive species will start to respond over time and adjust their behaviors.” There are a few historical examples. On the Spanish Cíes islands, for example, native birds called shags shifted their nests to sites less vulnerable to invasive minks. In Australia, native snakes evolved resistance to the toxins of invasive cane toads, and ate fewer toads. Analogous adaptations could be happening here, according to Taillie.

But, he continues, “I would be surprised if there was enough of that to decrease the population of pythons in any significant way.”

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“If they’re recognizing this invasive [species] as a food source, that’s a glimmer of hope,” agrees Adams. “That will be a piece of the puzzle, a very tiny sliver of management for maintaining healthy native species. But that alone doesn’t even come close.”

Animal dynamics won’t eradicate pythons on their own, but Taillie says neither will state hunting programs, which are at the mercy of taxpayer funding. Plus, he says, “Finding a python in the Everglades is like finding a needle in the haystack. And it’s a really large haystack. You only need a couple to survive, and then they can bounce back.”

“It’s not realistic that we’re going to get rid of all of them,” Kirkland agrees. But with the right technology, he thinks they can drive python numbers down enough that native animals will return: “The technology is updating itself every day. We’re trying to stay on the cutting edge of that.”

One of those methods is tagging pythons and tracking them to learn about their habits and to find other pythons. Miller’s team has tagged the snakes during the breeding season, when multiple males congregate around a female. “If you tag a male, he can lead you to where these breeding events are happening. And then you can remove all the snakes,” she says.

Others now tag pythons’ prey, like rabbits, raccoons, and opossums. When the snakes swallow the prey, they swallow the tag. It’s then easier to study or euthanize them. University of Florida researchers also tried putting rabbits in snake-proof cages in the Everglades to lure pythons closer to remote cameras. Nine rabbit pens lured 22 pythons over 90 days, and each stayed in the area for over an hour on average, according to a state report. “It sounds like a simple idea—and it is—but it’s also brilliant. It’s another way to get at these hidden pythons that we probably wouldn’t otherwise have found,” Kirkland says. Combining rabbit scents and remote traps might yield the same results.

Another idea referenced by the USGS paper pairs near-infrared cameras with an algorithm trained to detect the Burmese python’s unique markings. The system would display the snake onscreen as a bright white object that could be tracked in real time. Kirkland’s team has been involved in early testing, and he envisions equipping trucks and drones to find the most well-hidden invaders. “That’s still being dialed in. but it shows some promise,” he says.

USGS scientists are also wondering if gene-editing technology could help. Scientists could modify female snakes to only birth male offspring. After many years, the dearth of reproductive females would bottleneck the population. (Researchers have previously released genetically engineered mosquitoes in Florida to produce a similar population crash.) USGS scientists are exploring the feasibility of this idea, but concrete plans are still far off.

So for now, the state mostly relies on patrols like Kirkland’s. After his bout with the 17-footer back in 2018, Kirkland hauled the dead snake away in the back of his GMC, affectionately named Python 1. Five years later, he now cruises the wetlands in a new truck, Python 2. The mammals still haven’t returned. The snakes still haven’t left. But he speaks with a confidence you’d expect from a guy who grabs giant snakes by the head. “I’ve got about 20 years until I retire, and I’m really optimistic that we’re going to be in a better place by then,” he says. “But these things take time.”

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