Burmese Pythons: Guilty until proven innocent

[iCandiBallPythons]

Scientists brought 10 Burmese pythons to South Carolina to test the validity of one study that said the snakes could survive as far north as Washington, D.C.

With thousands of Burmese pythons and other giant invasive snakes devastating wildlife in the Florida Everglades, the hottest question on many minds is: How far north could they go?
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New research shows the snakes can withstand surprisingly cold temperatures, leaving open the possibility that their range could extend hundreds of miles northward.

Burmese pythons have been crawling amok in South Florida since at least the mid-1990s. The population's forerunners were probably released by pet owners daunted by the prospect of maintaining a predator that can grow to 20 feet (6 meters) long and weigh 200 pounds (90 kilograms).

No one knows exactly how many there are now, but estimates put their numbers in the thousands or tens of thousands. The pythons have been devouring local wildlife, indulging in mega-meals like deer, bobcats and alligators, as well as endangered species like the woodstork and the Key Largo woodrat.

So far the Burmese python invasion is restricted to Florida's southern tip, but scientists have been debating whether it could spread to more temperate parts of the United States. After all, the species' native range includes the foothills of the Himalayas, so it is no stranger to cold. One alarming study by the U.S. Geological Survey in 2008 predicted the pythons could find suitable climate in about a third of the United States, as far north as Washington, D.C.

How cold can you go?

To test those predictions, researchers recently brought 10 adult male pythons from the Everglades to South Carolina, to see whether they could survive the cooler climate. After implanting a radio transmitter and a temperature logger in each snake, the researchers let them loose in June 2009 in a snake-proof outdoor enclosure.

All 10 pythons did well through the summer and fall, and even survived 12 December nights that were no warmer than 41 degrees Fahrenheit (5 degrees Celsius). Then, in January, the region was plunged into an extremely unusual cold spell. With temperatures dipping below freezing at night for long stretches, the 10 snakes died, according to a paper published in September online in the journal Biological Invasions.

Still, said study leader Michael Dorcas of Davidson College in North Carolina, "there certainly is a possibility that pythons could survive in South Carolina and possibly even farther north."

For one thing, the subfreezing temperatures were highly unusual for the region. For another, some studies indicate that the temperatures a snake experiences during its first year determine how it regulates its body temperature for the rest of its life. Snakes born in the area might fare better than snakes transplanted in as adults.

Finally, the pythons that survived the longest were the ones that crawled into underground cavities at night, and Dorcas wonders whether they might have fared even better outside the enclosure.

"There are certainly in South Carolina much deeper retreats that they could have found if they were out in the wild, such as armadillo burrows," Dorcas said. “If we provided deeper refugia, well, would they have survived? We certainly had snakes that survived a long time and were finally killed by the extreme cold snap we had in January. But snakes had survived many nights where it got below freezing.”

Florida cold snap

The same cold snap that killed the South Carolina transplants also killed many Burmese pythons in the Everglades. Nine of 10 radio-tagged pythons there died, researchers reported in another Biological Invasions paper, published online in June. That sounds like a good proportion, but extrapolating to a population of thousands leaves plenty of snake survivors, said Skip Snow, a wildlife biologist based at Everglades National Park who contributed with Dorcas and others to the study.

In the months since the cold snap, adults and 24 hatchlings have been spotted in the wild, according to Snow. That's about the same number of hatchlings found by this time last year, so clearly the wintry weather didn't set the population back much. Whether the surviving pythons have genetically based adaptations to the cold is unknown, but if so, said Dorcas, "then we just had a major selection event for cold-tolerant pythons."

What it all means for the pythons' ability to invade farther north remains to be seen, but Snow takes the long view: "The snakes are going to tell us. They're clearly here, and they're breeding and they're established and they're going to tell us over the years and over the decades just what they can put up with and how far they can go."
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If Snow doesn’t sound very hopeful that the snakes can be eradicated, it's because they're so secretive, and the Everglades are vast, largely inaccessible, and full of hiding places. "We have no proven eradication tools for introduced reptiles anywhere in the world, really. It's never been done, and we have no studies to go to, that say: 'Yep, if you do these things you can eradicate an introduced reptile.' Our toolbox is empty of proven tools," he said.

Not that he and other managers aren't trying. The current strategy focuses on containing the pythons' range, stubbing out isolated populations, and targeting areas where pythons are particularly destructive, such as near bird colonies.

Public involvement is also key. The latest tactic on that front is a new smartphone app that serves as a field guide to the region's big reptiles. Eventually the public will be able to transmit sightings, photos and GPS data to help authorities track invaders.

The state of Florida allows hunters to kill pythons and other invasive snakes on certain state lands — but warns them not to eat their quarry, after the discovery that Burmese pythons contain extremely high mercury levels.

Other invaders

Compounding the problem are other giant non-native constrictors on the loose in South Florida. A smaller population of boa constrictors is known to be established, and last year researchers confirmed that African rock pythons were breeding just outside Everglades National Park, not too far from Miami. That species can grow to 20 feet and is notorious for its aggressive temper. A multi-agency effort to track and curtail the African rock python population before it can increase its range is under way, including a plan to enlist snake-sniffing dogs.

"We really don't know what the capability of that species is to spread. It seems to have similar characteristics to the Burmese python, so perhaps it could," said Christina Romagosa of Auburn University, who is helping with the African rock python survey effort.

Ban on snakes

Recent legal changes may offer some help. On July 1, Florida implemented a ban on importing or acquiring Burmese and African rock pythons and four other non-native snake species. People who owned these species before the ban went into effect can keep their animals if they microchip them and maintain a $100-per-year permit.

The U.S. Fish and Wildlife Service has also proposed listing nine species of large constrictors as “injurious wildlife” under the federal Lacey Act, which would prohibit people from importing them or transporting them across state lines without a special permit. The service has collected more than 50,000 comments, and said a final decision could come next year.

As for Florida’s pythons, the genie is already out of the bottle. But it’s not too late to prevent the next invasion, considering how popular big snakes are in the pet trade, said Snow of Everglades National Park.

“We’re bringing them into the county under the idea that they’re all innocent until proven guilty. But we have historically had such a high standard of guilt, if you will, that it requires these animals to first of all escape, establish, get out in the wild, breed, and do something egregious like eat something that someone likes,” Snow said. “By then it’s way too late.”

[Dragoon]

this is what I hate about the scientific and legal community, everything is up for interpretation. 'We did a scientific study that proved the pythons cannot move north, but it still will happen because I said it could rather than test if it could.' What happened to integrity in experimentation? Was the scientific method edited to include a section on ignoring data to further your goal at the expense of integrity? I wonder if they can print the report on toilet paper so I can put it to good use.

[iCandiBallPythons]

Politicians along with some good lobbyists my friend

[Denial]

people are morons. If I have the air on in my house one of my burms would probably get a r.i. if they didnt have there heat on. Theres no way there could be a wild population of them in south carolina.

[TrpnBils]

If I'm not mistaken, isn't the leading cause of death in captive burms from RI? This would suggest to me that either they're more susceptible to it than other species, or they're less able to handle the stresses of the RI.

Either way, I don't see them going much farther north than Florida. Look at the USGS study's map...it has them ranging up as far north as southcentral Pennsylvania!!! If you compare that to a USGS map of average yearly temperatures, it doesn't make any sense that they could survive that far north. On those maps, the only areas that have an average high temp of 75+ is exactly where the burms are found right now... South Florida (Southern Texas is also there, but I don't know if the habitat is right in that area).

Ridiculous.

[Russ Lawson]

Well, the USGS map only used average temps, which is a terrible way to go about getting accurate results for the potential invasive range of a poikilothermic species. Additionally, data was compared with the entire range of Python molurus, which includes the Indian python, which can tolerate cooler temperatures. This is before even taking into consideration that Burmese pythons in the pet trade in the United States were only taken from a small area of that entire range. Different members of the same species can be quite different physiologically in different populations, and most of the imported Burmese pythons in the US pet trade are from more of the tropical populations in their range.

Bottom line: The USGS had a specific aim with their study and fabricated "science" to attempt to reach it. Now other scientists are forced to perform experiments due to the conflicting information provided by this and another study (Pyron et al, 2008). Unfortunately, it seems some like the one in South Carolina just want to make excuses and deny the accuracy of their own results. Sounds quite counter-productive to me, but it's a lot more difficult to get unbiased journals when people stand to make a lot of money if their findings support one of the sides over the other.