By Douglas Page © 1999

 

In a piebald wildlife management reserve near the Carolina coast, Davidson College herpetologist Michael Dorcas recruits eastern diamondback rattlesnakes to serve the interest of conservation biology. The diamondbacks enrolled in his research carry radio transmitters and data loggers in their body cavity, surgically implanted by Dorcas himself. Douglas Page profiles this research, and how Dorcas and his colleagues stay safe while handling the most dangerous snake in North America.

In a small clearing in the stunted shrubs and spindly wiregrass clumps that dress the dry lowland dunes under the cabbage palms and pinelands near the Carolina coast, an eastern diamondback rattlesnake waits in a concentrated, deadly coil in the shadow of a fallen tree. Able to move only 3.2 km per hour, it must often wait for its prey - ground squirrels, rats, mice and rabbits - to come to it.

Its tongue flicks, sampling the air. A snake smells with both its nose and tongue. Tiny particles which carry odor catch on the tongue, which the snake 'smells' when they are pressed against sense organs inside its mouth.

Like other members of the pit viper family (Viperidae), the eastern diamondback rattlesnake (Crotalus adamanteus) has unique organs located in 'pits' just behind its nostrils and slightly in front of its eyes for sensing temperature differences in objects around them, necessary for locating warm-blooded prey. Rattlers do most of their hunting at night or early morning, when rabbits are most active. With this built-in infrared heat sensor, a diamondback can detect warm-blooded animals 50 cm away. Studies have shown, when the 'pits' are covered the snake has difficulty striking its prey and may miss entirely. The eyes are adequate only for seeing close objects.

The snake, which can grow to 1.83 m in length (the record is 2.44 m), is identified by dark brown or black diamond shaped patterns on its body, outlined boldly by rows of cream-colored or yellowish scales. Two oblique white stripes inscribe either side of its head like contrails against a mottled sky.

The Rhythm of Human Footsteps

Suddenly, the ground begins to vibrate, faintly, increasing, pounding the rhythm of human footsteps. The heavy, humid air seems to move with the murmur as a man steps abruptly into the clearing, stopping less than 1 m from the largest and most dangerous of all venomous snakes in the United States.

The snake freezes. It does not rattle. It does not strike. The snake's venom is its last resort, used in self-defense. Of more than 115 domestic species of snakes, 20 are venomous, including 15 species of rattlesnakes, yet the chances are greater of dying from drinking dish soap than from a poisonous snakebite.

If this snake is lucky, the rustling disturbance in the tenuous serenity is caused by Davidson College herpetologist Michael Dorcas, and not a vitriolic rattlesnake hunter intent on liberating the region of a perceived menace. "For the most part, diamondback rattlesnakes are reluctant to actively defend themselves," Dorcas says. "We've never had a snake strike, unless we messed with it first. The snake is just hoping it doesn't get seen or stepped on. We've never just walked up to one and had it strike. They prefer to escape."

Dorcas is in the bush, usually with colleagues Wade Kalinowsky and Steve Bennett of the South Carolina Department of Natural Resources (DNR), recruiting eastern diamondback rattlesnakes for a lengthy research project assessing the physiology and behavior of a species disappearing at an alarming rate. Suburban housing and agricultural development continually devour vast areas of snake habitat, which already is listed as threatened on some state Endangered Species lists - but not, however, by the federal government. Sanctioned slaughters called 'Rattlesnake Roundups', held annually in several states, further decrease their numbers.

A key to understanding reptile and amphibian conservation problems nationally and globally lies partly in recognizing their importance in the U.S. southeast, the region with the highest domestic biodiversity. For several years, international attention has focused on amphibian declines and deformities elsewhere. Bruce Means, president of the Coastal Plains Institute and Land Conservancy in Tallahassee, Florida, says, "Amphibians and reptiles play a much more important role in nature than most people realize, but they have not been given the conservation attention they need. The southeastern United States has more snakes, frogs, salamanders, and turtles than anywhere in the U.S. and Canada, but most are unknown to the public and many are in serious trouble."

Dorcas' work, in collaboration with the South Carolina DNR, contributes to the development of a management plan to protect and conserve the species by attempting to understand their environmental requirements, movement patterns, and population ecology.

"The eastern diamondback have been wiped out from a lot of places they historically lived," says Dorcas. "In North Carolina, there are very few viable populations left. Even in South Carolina there aren't that many big populations remaining. Habitat destruction is one reason, but also people like to go out and kill them, or collect them."

Belts, Boots, and Hat Bands

Dorcas collects them, too, but for a reason other than separating the snake from its beautiful, rugged skin, to be fashioned into belts, boots and hat bands. Others, vandals blinded by irrational fears and misinformation, collect just part of the rattlesnake, which might otherwise live 20 years or more, slaying them merely to measure their manhood by filling mayonnaise jars with rattles.

Dorcas is doing what he can to save the species from annihilation. "They are an irreplaceable part of the coastal plain ecosystem," he says. "They are major predators of small mammals (rats, mice, rabbits), which helps control these populations. They aren't as dangerous as people think, if you leave them alone. From my perspective, they are an amazingly beautiful and interesting animal that deserves our attempts to understand them. They have an inherent right to exist. They were here before us."

In order to understand them, information about reproductive rates, diet, thermoregulation and how it relates to their habitat requirements, the snakes must be tracked and monitored. This requires radio transmitters and data loggers, equipment which must be implanted in the snake, which, of course, must first be caught.

The World's Largest Rattlesnakes

"Basically, we use a snake hook and try and hook them into a bag, all the while being very careful," says Dorcas. "These are the largest rattlesnakes in the world and the most dangerous snake in this country. Consequently, we're extremely careful. We try to disturb the animal as little as possible so they aren't actively defending themselves, or trying to escape down a hole." Because they're so careful, and because they wear snake-proof chaps over their trousers, no one connected with the study has been bit yet.

Rattlesnakes, which can spring one third of their body length with electric speed, inject their prey with a poisonous venom, driving two needle-sharp fangs into the target. As the fangs penetrate, muscles pump the venom out tiny holes on the tips of the fangs. The rattler then quickly disengages and moves away, waiting for the venom to disable the victim. The strike happens in what appears to be a single, swift shock taking less than a second. The prey is usually bitten only once, then allowed to crawl away and die. The snake waits, determines when the prey is dead, then devours it, head-first. Rattlesnakes are able to digest even the bones.

When humans are bit, fatalities are rare. Venom toxicity varies between individual snakes. Symptoms from diamondback envenomation include pain, swelling, weakness, breathing difficulty, weak pulse, heart failure, shock, and sometimes convulsion.

"For the most part, the snakes are pretty laid-back," Dorcas claims. "Certainly there is some danger inherent in tracking the snakes. We try to take as few people with us as possible, and those we do take follow at a safe distance."

If the snake Dorcas finds is already enlisted in the study, it's caught, weighed and released.

If the snake is a 'new' snake, he and his colleagues take it to a nearby lab and surgically implant a radio transmitter and data logger, each about one-third the size of 35 mm film canister. "It's a simple surgery," he says. "These snakes are big, heavy-bodied animals with lots of space inside. If the snakes were small we wouldn't be able to do this." Eastern diamondback rattlesnakes, however, frequently have the girth of a man's upper arm.

Using a ketamine general anesthetic, Dorcas places the equipment inside the snake's body cavity, posterior to the stomach.

Getting the Snake to Submit

Getting the snake to submit isn't quite so simple. "When we do the surgeries, we use a clear plastic tube that's like a big, stiff, transparent soda straw," Dorcas says. "Instead of pinning the snakes head and picking it up behind the neck, as is common practice, we take the tube and have the snake crawl up inside it."

After a "little maneuvering" to get the tube over its head, they coax the snake to crawl in further by taping on its tail. Once about half its body is inside, the Dorcas crew restrains the exposed part, holding it with the head well inside the tube, where it can be examined. "It's relatively unstressful for the snake," Dorcas says, "certainly less so than pinning it behind the head, which is dangerous and can also hurt the snake. In terms of handling, our risk is minimized, although I never want to say there's no way you're going to get bit."

The tubes are sometimes also used in the field to capture the snakes, although this is tricky. "In the field there are more variables to consider, different types of terrain. Out there, the animals may behave differently than they do in the lab," says Dorcas, whose wife's enthusiasm for this activity is largely restricted to 'professional' support. "Tammy tolerates it," he says. "She thinks it's interesting and she's excited that I'm doing what I want to do. She's confident I will do things in as safe a way as possible."

After a prudent recovery period the snake is returned to the field, to be tracked and monitored.

"Radio telemetry makes that easy," says Dorcas. "Generally, they're tracked every two days, located and noted what they're doing, whether they're out or underground."

Dorcas, Kalinowsky or Bennett strap on the chaps and meander out into the lowland littoral with directional radio telemetry receivers using signal strength to track the snake's location. "If the snake's on the surface we get a visual observation, try not to disturb it, and then go back after it moves to fix the exact location with differentially correcting Global Positioning System units so we can accurately map their movements and home range."

Although the number varies, at present Dorcas and colleagues are tracking eight eastern diamondbacks in the 5,866 acre wildlife preserve managed by the South Carolina DNR. What number of snakes is healthy for an area this size? "We don't really know," says Dorcas. "Hopefully, our research should shed some light on this."

They will track the snakes all year. In the winter, the diamondbacks don't move very much. Then, in the fall, the males move a lot because they breed in the late summer and fall. While the snakes aren't territorial, the males will "wrestle" during the breeding season for the chance to mate. Herpetologists call it "combat." "Many pit vipers do this," says Dorcas. "They don't bite, but raise the anterior portions of the bodies, intertwine them, and try and push each other to the ground. This is so rare I've never seen it."

After mating, the female stores the sperm until fertilization of the eggs takes place sometime in the spring. After six to seven months of gestation, she'll give birth later that summer, in safe retreats such as hollow logs.

Low Reproductive Rates

"Diamondbacks give live birth, like nearly all pit vipers," says Dorcas. "They usually produce a litter of eight to 15 babies, which is not a lot. They're relatively large babies, over 30 cm long. Diamondbacks only reproduce every two or three years, so when you go into an area and take out a bunch of them, especially large females, you can really decimate a population quickly."

The data logger records body temperature every 30 minutes for up to a year, says Dorcas, who attributes his interest in amphibians and reptiles to time spent camping and hiking with his father, Eugene E. Dorcas, as a boy in Texas. "He wasn't one of these people that believes the only good snake is a dead snake."

After about a year, when they replace a snake's radio transmitter before the batteries fail, Dorcas pulls out the data logger, plugs it into a computer and gets a complete body temperature record on the animal for an entire year.

The study has produced some body temperature surprises. "Because the eastern diamondbacks are so large, their surface area-to-volume ratio is relatively low, especially when they coil up," says Dorcas. "So they heat and cool considerably slower than other snakes." And these snakes, if they get caught on the surface during a cold spell in the early spring and the temperature drops below freezing, don't necessarily go below ground, he says. Instead, they stay on the surface and burrow into the pine needles (like sidewinders burying themselves in sand). The data loggers have recorded body temperature records close to 1 degree C.

There are other surprises. For instance, before this study, there was a preconceived notion that the eastern diamondbacks, which are found from the coast of southeast North Carolina, down to Florida and west along the Gulf Coast to Louisiana, spent their time in higher, drier, sandy areas. "We're finding they go down into the lowlands quite frequently," Dorcas says. "They're utilizing a lot more habitat than we thought. This has important conservation implications." Further research will be necessary to determine if this means they can live in different habitats and not be restricted to certain ones, or whether it may mean they require a variety of habitats.

Adult diamondbacks have little to fear except humans. Most humans will kill a rattlesnake on sight.

As maligned species go, snakes got an early start. What began with the serpent in the Garden of Eden myth endures in contemporary hysteria and ignorance. Their venom makes them even less appealing than other accursed species, such as bats, wolves, spiders and sharks. One of the most spiteful insults one can be called is "snake". Rattlesnake roundups - massive, flea-market like festivals designed to lure and relieve visitors of their vacation money - is this militant stupidity's most sinister expression.

Every year, hundreds of eastern diamondback rattlesnakes, among other species, are rounded up and brutalized in front of paying audiences. Not only do these rituals, some sponsored by national beer companies, deplete rattlesnake populations, the environment is damaged by 'sportsmen' who 'round-up' snakes by squirting gasoline down holes until something emerges. The burrow is thus rendered uninhabitable for years. The snakes, held captive for weeks in buckets, are then displayed, milked for their venom and otherwise abused, sometimes skinned alive, in front of customers.

The work of Michael Dorcas, and others with his passion for preservation, who patrol the perilous chaparral in pursuit of knowledge, provides a refreshing enlightenment in the face of this barbarism.

SUGGESTED READING

Ernst, C. H., Venomous Reptiles of North America, Smithsonian Institution Press, Washington and London(1992).

Greene, H., Snakes: The Evolution of Mystery in Nature, University of California Press, Berkeley, Los Angeles and London (1997).

Klauber, L. M., Rattlesnakes: Their Habits, Life Histories and Influence on Mankind, Vol. 1 and 2, University of California Press, Berkeley, Los Angeles and London (1972).

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