Monday, July 23, 2012

Try Not to Step on Any Pythons

     Last spring, as I stood in a dry marsh on the border of Everglades National Park, I paused to study the vast landscape. I squinted my eyes to make out any movement in the endless sea of green before me, straining to see my quarry as the morning Florida sun rose and drew sweat on my forehead while simultaneously baking the dirt into my skin. I was looking so intently because I knew there were large pythons hiding in the grassy vegetation right in front of me, several of them, up to thirteen feet long. But there was no clue that these massive snakes were just a few steps away, they gave not even a hint of their presence. The only reason I knew they were there was because I had put them there and the beeping radio-receiver in my hand told me that they hadn’t left.

The people walking around in the study plot in front of me, probing the tufts of grass with various poking instruments, hadn’t had much luck either. For all they knew, there weren’t any snakes there at all. I looked to the adjacent study plot and noticed a black labrador retriever prancing and bounding enthusiastically. It had found a python.


             A few weeks prior, I had been thrilled when my friend and colleague Christina Romagosa offered me the opportunity to help out on a study she was coordinating related to Burmese Pythons (Python molurus) in Florida. Burmese pythons, as you are likely aware from their name, are not originally from Florida, but you can be sure that they are there now. How they became established in the United States is a matter of some debate and controversy, but the most plausible story I have heard suggests that the thousands of pythons that now roam southern Florida descended from a small group of individuals that were destined for the pet trade but ended up escaping (or were released) instead, probably sometime in the 1980s. Since that time, additional releases and escapees have supplemented the rapidly growing population.
Melissa (on right) showed us the ropes
   Most of the time when a species is introduced to a new area, they disappear into the forest or some backwoods swamp and quietly live out their lives, perhaps quickly eaten by a native predator that takes advantage of the new creature’s naïveté in the strange land. But every so often, an organism comes along that makes itself right at home. Perhaps they are able to outcompete native species and use up more than their fair share of a limited resource. Perhaps, on the other hand, they skip the competition bit and simply excel at eating up all the natives. These introduced species are considered invasive, because they wreak havoc on native ecosystems.

When it comes to species displaced to areas where they are not native, you can imagine that Burmese Pythons are not the quiet type. Biologists have been sounding the alarm for some time now, alerting everyone that would listen about the potential effects of an established python population in Florida. Concern was raised about all the animals they pythons were likely to consume, including endangered wood rats, key deer, even Florida’s iconic swamp king, the alligator. No amount of concern, however, could stop the ecological process that was already underway. A recent scientific article describes how encounters of medium-sized mammals in the Everglades have decreased dramatically, a decrease that coincides neatly with the increase in the numbers of pythons. Put two and two together, and the most logical explanation is that as the python population increases, they are eating everything else into oblivion.

     That pythons are eating things is not a controversial suggestion. Where and when they will stop doing so is another matter. Scientists have tried to predict how far the python invasion will spread, as the giant snakes eat and slither their way across Florida, but different predictions (i.e., models) have led to different results. There was even a study done in South Carolina to determine if Burmese Pythons could survive the winter in areas less tropical than Florida (the verdict: not really). But, in any case, what we can all agree on is that today, southern Florida, and most notably, the Everglades National Park, is overrun with exotic giant pythons.

    However, determining if there are any pythons in any specific spot can be a tricky matter. Snakes are exceptional at camouflage and in being inconspicuous in general. Christina wanted to know how good we can be at finding pythons, and by extension, evaluate our ability to determine when and where the population was spreading. We are at a disadvantage though, when compared to canine searchers. Dogs are well known for their ability to sniff out drugs and bombs; but recently, biologists have taken advantage of their exceptional sense of smell and trained some dogs to find things like snakes. Large study plots in the grassy areas just outside the border of Everglades National Park were to be filled with zero to three pythons. My job (for the week) was to help keep track of how long it took people to find the snakes (or, sometimes, how long it took them to tell me that they gave up) and, separately, keep track of how well detector dogs fared in other plots.

A typical study plot. See the pythons? Me neither.
On my first day, I was skeptical. The study plots reminded me of somebody’s freshly mowed front yard. How in the world, I imagined, could a ten-foot (or larger) animal escape detection for more than 30 seconds in this type of habitat? The answer, it turned out, was quite easily.

In the morning, before the searchers (both humans and canine) arrived, we drove through the study plots and dropped pythons out of the back of a pickup truck. It was necessary to do so because otherwise the dogs would have cued into our scent, leading them right to the snake. I watched with amazement as the pythons uncoiled themselves, took survey of their surroundings, and then just disappeared into the undergrowth.

Trying to remember how radio-telemetry works
The pythons we were using for the study had all been captured in and around Everglades National Park. And, as you can imagine, there was some concern that the pythons would escape and crawl right back. So, each snake was implanted with two radio-transmitters (one a back-up in case the first failed) that allowed us to keep track of its location. Before any searchers began looking for the snake, I walked the perimeter of the study plot with the radio-receiver, confirming that the snake (or snakes) was still within the boundary.

The highlight of the experience for me was when I was supervising two individuals tag-team a study plot. They were covered in expedition gear, looking like a combination of Crocodile Dundee, Steve Irwin, and the Predator.

Bagging a python at the end of the day

 They confidently strode through the grassy study plot, chatting and occasionally investigating a shrub or two. When they finished, in record time, they pronounced their disappointment at being assigned a plot with no snakes.

“Would you be surprised if I told you that there was a python in this study plot?”           

Surprised? They wouldn’t believe me, they said.

I admit I took great pleasure in then leading them around the study plot and showing them not one, not two, but three pythons hiding among us. I don’t know how they avoided stepping on any of the great snakes, which together measured about thirty feet.

At the end of each day, my partner and I retreated to the Key Largo cabin we were provided for helping out on the project. While eating on the dock and drinking margaritas as the waves lapped against the shore or kayaking around the bay as storm clouds gathered in the distance, I imagined that I was finally getting to enjoy one of the perks of being a field-biologist, that is, helping out and doing field work in exotic and tropical locations. The thrill, however, was somewhat diminished by the 4:30 am wake-up calls. It was necessary, after all, to drive into the park and set up the study plots with pythons before the searchers arrived (at a much more reasonable hour). Exhausted by the sun and our schedule, we stayed awake to explore the Everglades only once. The manatees cooperated and revealed themselves to us, on the other hand, the American Crocodiles (Crocodylus acutus) did not.

            Monitoring plots wasn’t the only task at hand. Christina was also interested to know whether people and dogs could find pythons in areas that more closely resembled the habitats that pythons preferred, that is, the canals that crisscross much of South Florida. The brush and vegetation surrounding many of these canals were dense and overgrown, perfect hiding spots for snakes, which occasionally slip into the water to hide.  Because of concerns about live pythons disappearing into the drink, these trials involved us hiding a thawed out (and very dead) python.

In driving to one of these canals, we were all surprised when a silver streak jetted across the dirt road in front of us. Both the labrador and their trainer, Bart, (who were walking the road while we followed slowly in the air-conditioned truck) were shocked motionless as the streak appeared from one side of the road and, just as quickly, vanished into the other. Before we could get our bearings the creature appeared once again and disappeared into the brush from where it had first emerged. It was an incredible feeling to realize I had just seen (albeit briefly) a tegu, a large lizard distantly related to the racerunners found throughout the Southeastern United States. I didn’t expect to find them here, far from their native range in South America. Stocky and voracious predators, tegus are yet another emerging and invasive threat in Florida.

Driving back to Auburn after the week in South Florida, I reflected on how the dogs were exceptional at finding hidden pythons. Humans, on the other hand, performed decently. Would either be able to accurately inform us about the spread of pythons through the wilds and swamps of Florida? It’s unlikely we have enough dogs, or people, for that matter, to accomplish that feat.

Any story mentioning the Everglades must include photographs of alligators

Want to learn more? Check out these scientific articles:

Dorcas ME, Willson JD, Reed RN, Snow RW, Rochford MR, Miller MA, Meshaka WE Jr, Andreadis PT, Mazzotti FJ, Romagosa CM, & Hart KM (2012). Severe mammal declines coincide with proliferation of invasive Burmese pythons in Everglades National Park. Proceedings of the National Academy of Sciences of the United States of America, 109 (7), 2418-22 PMID: 22308381

Pyron RA, Burbrink FT, & Guiher TJ (2008). Claims of potential expansion throughout the U.S. by invasive python species are contradicted by ecological niche models. PloS one, 3 (8) PMID: 18698351

Rodda GH, Jarnevich CS, & Reed RN (2011). Challenges in identifying sites climatically matched to the native ranges of animal invaders. PloS one, 6 (2) PMID: 21347411

M.E. Dorcas, J. D. Willson, & J. W. Gibbons (2011). Can invasive Burmese pythons inhabit temperate regions of the southeastern United States? Biological Invasions, 13, 793-802 DOI: 10.1007/s10530-010-9869-6

J. D. Willson, M. E. Dorcas, & R. W. Snow (2011). Identifying plausible scenarios for the establishment of invasive Burmese pythons (Python molurus) in Southern Florida Biological Invasions, 13, 1493-1504 DOI: 10.1007/s10530-010-9908-3

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