By Carol Bogart, Sacramento Nature Examiner
Remember that horror story some years back about hordes of pythons migrating out of Florida swamps heading for, among other places, California?
Well, um, relax.
“Lots” has changed in the python-studies world since the U.S. Geological Survey published in 2009 python migration maps drawn in 2008. The maps, says USGS scientist and snake expert Dr. Robert Reed, were misconstrued as outlining areas of the country where now and future huge snakes might busily be making babies.
The maps, he explains, show only areas of the country with climates similar to, for example, the Burmese python’s native habitat in Asia. Suitable climate, he says, does not mean pythons now happily living in the Everglades will decide to move to California.
In fact, a new study recently published in “Biology Letters”and just released by USGS reports that six pythons were fitted with tracking devices after they were caught. They were released up to 22 miles away. Slithering similar to how the crow flies, they went right back to within three miles or where they’d been captured in Forida's Everglades.
Demonstrating a ‘map sense and a compass sense,’ the snakes navigated using, among other things, landmarks and the light from stars. The released snakes’ return to where they were captured “indicates that not only do pythons keep their long-term movement goal in mind, but also that they were highly motivated to get back home,” said study co-author and USGS researcher Kristen Hart. Hart collaborated with a multi-organizational team of scientists that included Shannon Pittman. Pittman, the lead author of the study, is a postdoctoral fellow at Davidson College in North Carolina. She said, “Previous studies have shown that many snakes lack the ability to home, yet this study provides evidence that Burmese pythons are capable of homing after they have been displaced – and they are able to do so at a scale previously undocumented for any snake species.”
Dr. Reed acknowledges that his Ft. Collins, Colorado office doesn’t track pythons surviving on their own in California. He says, “While observations of aquatic invasive species are tracked by USGS colleagues, there is no equivalent national database for terrestrial invasive species.” In other words, we know a lot about invasive species in water such as mussels, less so about enormous snakes settling in somewhere on land.
The python expert adds, “Captive pythons escape or are released with some frequency, so it would be expected that the odd python (Burmese, ball, reticulated, or other species) would show up in Calif. once in a while.” He said a report on exotic reptiles worldwide lists four pythons captured in Calif., but adds, “Only a small proportion of captured animals end up being reported in the scientific literature so there are probably more out there.”
Dr. Reed says his web search found a Burmese python that was captured near Lake Elsinore in Southern California, but again, the snake was likely a one-time pet snake that got out or was thrown out by its owner.
Even in Florida, the snakes don’t seem to move around a whole lot, he said. “The number of pythons captured has certainly increased in the Northwest part of the range around Tampa over the last couple of years, but there does not appear to have been a major expansion of the range in Florida overall over the last few years.
“It’s far more likely that new populations in places like Texas or Calif. will arise due to releases or escapes from captivity rather than due to expansion of the Florida population. The latter would be expected to take a very long time even if intervening climates are suitable.”
Even if pythons, under siege in Florida, did start migrating toward California within our lifetimes, Dr. Reed notes that a lot of big snakes in Florida were wiped out during 2010’s unprecedented cold snap. He says “it seems plausible that warmer temperatures would allow additional northward expansion by reptiles,” but adds “the particular strain of pythons in Fla. might have restricted cold tolerance as compared to the species as a whole.”
Dr. Reed says there are no known examples of pythons surviving for extended periods in Calif., adding, “but then again how could you tell if a captured python was a recent release/escape versus being a long-term resident?”
He says the main point is that ranges may expand a bit with climate change and while his personal opinion is that Northern Calif. isn’t at high risk of python invasion, the data are currently inconclusive. “The short answer is,” he says, “we don’t know how far they’ll spread.”
Referring to the results of the new python homing instinct study, Hart, the USGS co-author, notes: “The fine-tuned navigational capacity that the (tracked Burmese) pythons exhibited may lower their risk when they move to and explore new areas.”
ABOUT ROBERT REED, PhD: Dr. Reed is a snake ecologist by training. He is Chief of the Invasive Species Science Branch at the USGS Fort Collins Science Center, where he manages the Invasive Reptiles Project. He conducts research on Burmese pythons in Fla., brown tree snakes on Guam, invasive water snakes in Calif., and other problematic reptile invaders in order, he says, “to provide the best available science to resource managers and other stakeholders.”
MORE ON THE HOMING STUDY: “Homing of invasive Burmese pythons in South Florida: evidence for map and compass senses in snakes” by S.E. Pittman, K.M. Hart, M.S. Cherkiss, R.W. Snow, I. Fujisaki, B.J. Smith, F.J. Mazzotti, and M.E. Dorcas, is published in the journal Biology Letters. The study can be accessed online. FAQ