Friday, April 30, 2010

Which Came First, the Snake or the Egg?

This fall, a few colleagues of mine were hiking around southwestern Georgia when they noticed a familiar serpentine shape alongside a fallen log, a timber rattlesnake. Closer inspection revealed almost two dozen newly born rattlesnakes huddled together with their large and likely exhausted mother. Just a few months before this auspicious find, a kingsnake captured at the same site was being held for further study in the lab when it surprised everyone by laying over a dozen leathery eggs. The eggs were placed within an incubator and thirteen tiny kingsnakes were safely released into the forest after they hatched.


We call both animals snakes, yet they have vastly different reproductive strategies. Although timber rattlesnakes give birth to live young, kingsnakes lays eggs. Let’s take a moment to think about how unusual this is. What if half of all monkeys laid eggs or if babies popped out of some of the animals we collectively refer to as ducks or geese? Rat snakes, hognosed snakes, coral snakes, and indigo snakes lay eggs, but copperheads, water snakes, and garter snakes have babies. Why the dichotomy? It would be logical to assume all snakes that lay eggs are more closely related to each other than they are to snakes that give birth to live young, but that’s not always the case. And that suggests different groups of snakes independently altered the way they reproduce.


It is generally accepted that the ancestor of all snakes laid eggs, so there must have been some advantage for certain snakes to develop an alternative strategy. To investigate this further, we must look for clues that would indicate why giving birth would increase the survival of offspring. If more offspring survive, then they have a better chance of passing along their parent’s genes, and thereby a better chance of passing along any advantageous trait to further generations. Those that philosophize about these matters observed that species which give birth to babies tended to be from more northern climates (notice I used the word tend because we can almost always find exceptions to patterns observed in nature). Using this clue, we can attempt to imagine why snakes in colder areas found it advantageous to abandon egg-laying.


Snakes are ectothermic (you may be more familiar with the term “cold-blooded”), which means they rely on the external environment to regulate their internal body temperature. Referring to reptiles as “cold-blooded” has fallen out of favor because researchers determined snakes have a remarkable ability to maintain temperatures comparable to ours, just through their behavior. So, in northern regions where temperatures can get cold and unpredictable, you can imagine it’s more beneficial to develop inside of a large snake than an egg exposed to the elements.

Because a mother snake is warmer than an egg, babies develop faster. And a faster developing baby will have more time to find a safe place to hide before the onset of winter, another advantage. That some snakes developed live birth due to these survival advantages is generally referred to as the “cold-climate hypothesis”. Recent research has suggested snakes that develop under constant temperatures are simply faster, healthier, and survive in greater numbers than snakes that develop under more unpredictable scenarios.


There are likely other advantages to giving birth to live young, regardless of the temperature. For example, if you’re a raccoon or a fox and you come across a nest of snake eggs, the chances are pretty good you’re going to take advantage of this easy meal. Now, what if you come across an angry mother rattlesnake full of babies? In this case, you may realize there’s no such thing as a free lunch. It’s not hard to imagine why some snakes have found this strategy to be an advantage.

After this discussion, you may ask yourself if there is any benefit to a reproductive strategy that includes egg-laying. There are in fact some upsides. It requires a lot of energy to produce a fully functioning animal inside you, when a snake lays an egg they’re able to save some of that energy, perhaps better equipping themselves to produce a lot of eggs at one time or breed more frequently. Although eggs may be more likely to be eaten than live young, there can be enough eggs laid to make up for this difference.


You may have noticed that I did not use some scientific terms you’re familiar with, such as viviparity, oviparity, or ovoviparity. As with so many other aspects of biology, it’s sometimes hard to characterize animals with terms we make up, because there are often cases where a species does not cleanly fit into a particular group. That’s the case with snakes, and there is some debate among scientists just how to best characterize all the different reproductive strategies that snakes exhibit.

Pictures here appear courtesy of Fingerprince Prints Photography.

Thursday, April 22, 2010

Round 'em up


This column ran in the papers about a month ago...

It’s that time of year again, when people congregate in a few scattered festivals across the southeastern United States to celebrate the Eastern Diamondback Rattlesnake. Well, I guess celebrate isn’t the right word, since the snakes are eventually slaughtered. I certainly understand why people wouldn’t want rattlesnakes in their yard, but I’m not quite sure I understand the appeal in capturing snakes in the wild, far from human establishment, only to kill them. I remain unconvinced by claims that these rattlesnakes serve some greater purpose, with their venom being important for medical research. Why wouldn’t captive rattlesnakes serve the same purpose? And what companies are buying venom for research from a weekend festival in small town USA?

I concede rattlesnakes aren’t particularly loved by many and catching them for roundups isn’t illegal; unless of course, while catching rattlesnakes you deal irreparable harm to other protected creatures or their habitats. In the past, pouring gasoline down gopher tortoise burrows was a popular method of catching rattlesnakes. Groggy from the fumes, snakes leave the burrow and are easily bagged. However, any tortoises hiding within the burrow stay underground and may suffer severe lung damage. You probably know tortoises are increasingly rare, being federally protected in the western portion of their range and a candidate for listing everywhere else.

Publically, rattlesnake hunters will never acknowledge they continue to catch rattlesnakes by pouring gasoline down gopher tortoise burrows, an illegal practice. Although, an individual associated with one of the remaining roundups admitted to me the practice still occurs. But, I admit anonymous sources don’t carry a lot of weight. That’s why I recently read with interest about a few people cited for destroying wildlife habitat in Silver Lake Wildlife Management Area, in Georgia, on January 28th. These individuals admitted they were catching rattlesnakes by pouring gasoline down tortoise burrows. We can only guess as to why they were motivated to capture these snakes or what they had in mind for them. But, in any case, this should be clear and unequivocal evidence that people are still pouring gasoline down tortoise burrows in areas where we hunt, fish, and recreate.

So here we are, time for the annual rattlesnake “festivals” again. If you plan to attend, feel free, but go with full knowledge of what you’re supporting with your money. All remaining roundups in the southeast have been approached by multiple organizations and individuals eager to help them transition from events that sponsor rattlesnake capture and killing to more wildlife friendly events. Because they’re important to local communities, nobody wants these festivals shut down, but there are compromises that will help ensure the integrity of our natural habitats and wildlife. Perhaps you’ve attended Fitzgerald Georgia’s annual festival (a former roundup) or San Antonio Florida’s rattlesnake celebration, where thousands of people attend each year to see captive snakes displayed. Whether you hate rattlesnakes or love them, I think it’s time we all agree that wanton destruction of wildlife and their habitats is not something we should support.

Thursday, April 1, 2010

Sirena's Front Porch

The Sirena Station, on the coast of the Pacific Ocean and within Corcovado National Park, isn't easy to reach. It took me seven hours of hiking to reach the rustic station, though there are more direct means. One could get there by boat, parting the waters full of bull sharks and crocodiles. Or, you could charter a small plane to drop you off on the Sirena airstrip, something I saw three times during my stay.

But, that's too easy. Corcovado is one of the wildest places left in this part of the world. And if you want to get there, you should have to earn it. That's why I was smugly satisfied with myself as I lounged on Sirena's porch and watched tourists stop by for the day.

The front porch was vast, spanning the extent of the station. It's the first sight one sees after emerging from the long and dark path from Los Patos. Adirondack chairs allowed us to relax here; with my feet on the railing I spent hours looking into the surrounding forest watching for wildlife. Toucans called incessantly as small flocks worked their way through the jungle. Daily, a troop of squirrel monkeys would forage within their favorite trees for insects, only occasionally revealing themselves in the sunlight before making their way off for the night. Scarlet macaws were a common sight as pairs flew across the horizon, emitting constant and raucous calls.

It was only after the sunset that things began to get unpleasant. With the darkness came a blanket of mosquitoes, and they voraciously searched for and fed on any exposed skin. There was a fungus on my foot, a result of hiking for hours in wet boots. My bed sheets, too small for the plastic mattress, were often damp from sweaty night sleeps. It wasn't a problem for my pillow, as I did not have one. My half exposed mattress was covered by termite fecal pellets, the supply renewed each day as the insects chewed through the wooden bunk above me. The water here was suspect, and we were warned of the potential for contracting Giardia, as last year's course had. Filtering water was strongly recommended, making it difficult to quench one's thirst in a moment's notice. Each day, it was necessary not to check for ticks, but to remove the invertebrates that had inevitably embedded themselves within your skin.

None of this bothered me, it's the price one pays for staying in this unique area. What bothered me were the tourists next to me on the porch, playing with their iPhones and keeping me from indulging in my wilderness fantasy.

Corcovado National Park

In Corcovado, as at all other sites, we spent our first full day become oriented and learning the area’s history. Our first night had passed without event; although our accommodations weren’t ready and the entire class slept side by side on plastic mats in a single room, I didn’t mind. Perhaps because I was more comatose than asleep, but I wasn’t bothered by the thin and occasionally odorous mattresses and I didn’t even notice the snoring that had so vexed some others as they cursed in the darkness (I resent any implication suggesting this was because I was the culprit).

We were instructed to pack light for Corcovado, as hauling our equipment into the remote site was a logistic challenge. I dutifully complied, bringing only a single pair of pants, a couple shirts, and leaving much of my gear behind; as the days passed, I would regret only that I didn’t have my rubbing alcohol, though others would’ve likely preferred I had a change of clothes. In any case, it didn’t take me long to decide what to wear before we headed out.

The forest that now makes up Corcovado National Park has a long and somewhat sordid past. In the early 20th century, the land was owned by the United Fruit company (based in the United States, this corporation was a heavily influential, and oft criticized, force in Central and South American countries in the early 1900’s). However, they didn’t make much use of the land; and as the forest went undeveloped, many squatters took up residence. In addition, gold mining began in earnest and small communities sprouted up within the forest to support this illegal activity. The Sirena station, where we were staying, was once the location of a seedy settlement that existed to satisfy the needs of the gold miners, providing staples like food, alcohol, and women. All for a price.

Selective logging occurred throughout the forest for the rest of the century until 1975, when the Costa Rican government acquired it and established Corcovado National Park. A protected land in name only, there remained problems with squatters, who were relocated, and gold miners, who weren’t as receptive to relocation attempts. Violent conflicts between guards and gold miners in the 1980’s forced the closure of the park. Understaffed and underfunded, Corcovado struggled. The Nature Conservancy was an early partner in bringing the park to its current status as one of the most treasured protected areas in Central America.

Now, Corcovado National Park represents one of the best places in the region to see wildlife that is rare elsewhere, like tapirs, white-lipped peccaries, jaguars, spider monkeys, squirrel monkeys, pumas, ocelots, and on and on.



Tapirs were on the top of my list to observe, huge beasts that can weigh hundreds of pounds, they’re distantly related to the horse and rhinoceros (these animals are grouped together because of the structure of their foot). There are four species across the globe, three of which are in Central and South America and one in Asia. Like many large animals, it takes tapirs a long time to reach maturity, and once they’re of reproductive age they don’t produce many young. After a baby is born they may stay with the mother for two years! A lot is invested into each animal; normally, this is okay, because adult tapirs have few natural predators. Not even a jaguar will have an easy time taking one down. But, they’re no match for a bullet.

The loss of just a few animals may reduce the population down the road, which is why hunting and poaching have been implicated as one of the major causes of the species’ decline. But, this threat pales in comparison with habitat loss. Once a rainforest is converted to other land uses, tapirs simply have less space to live. For a large animal that forages for fruits over a huge chunk of land, populations can’t maintain themselves in small fragments of forest. In the depths of Corcovado, poaching is not a great concern, and the vast amount of protected forest allows tapirs to thrive.

I spent an inordinate amount of time strolling through the forest looking for sign of tapirs. Day after day I walked the trails hoping to stumble across one of the beasts. I found many patches of dense vegetation where tapir are known to bed down; it’s thought the vegetation might deter hungry cats from venturing too close.

Although I wouldn’t necessarily feel safe there, I suppose you take what you can get when a jaguar wants to eat you. Occasionally, I would see their unique tracks in the sand along the beach or the shore of the Sirena River, but never the beasts themselves.


Tapirs are generally nocturnal but due to park restrictions night hikes were a rare event. The prospect of completing one was the subject of great anticipation for me, but these infrequent events did not produce the payoff I was hoping for. Another group however, did hear a tapir stampeding through the forest and caught a brief glimpse as it disappeared into the darkness.

Minutes after I fell asleep when hot and steamy night, I was awakened by a faculty member urgently asking me if I wanted to see a tapir. Groggily I removed my ear plugs as he repeated himself. I must not have looked as though I was operating on full cylinders as I stared at him quizzically, because he repeated himself a third time.

“If you want to see a tapir, there’s one in front of the station.”

Frantically, I threw on whatever clothes were within reach and stumbled out of the room and towards the front of the station. Despite assurances of a huge tapir there just moments before, there was no sign. Over the next few days, others would report to glimpses they had seen of these animals, but they successfully eluded me. That is, until the last possible moment.