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HERPS OF THE SOUTHEAST VIRTUAL WALK
Stop#: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 [17] 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

Stop #17: Hillsborough River State Park, FL
Featured Herp: Eastern Diamondback Rattlesnake (Crotalus adamanteus)

 

East Aiken continued their hike up the Gulf Coast of Florida, and arrived at Hillsborough State Park near Tampa/St. Pete on January 15, 2000. This State Park, opened in 1938, is an excellent setting for the hikers to begin their acquaintance with an inland portion of Florida they will see a great deal of in weeks to come—a sandhills habitat rich in live oaks, sabal palms, hickory trees, and occasional patches of sand pines, dotted with limestone sinkholes, and crossed by clear spring-fed rivers.

geographic regions of Florida

In geological terms Florida is a very young landform that has been covered by shallow marine seas numerous times. Repeated ocean advances and retreats, sand and clay deposition from streams to the north, a warm climate, and many other factors have combined to create the landscapes visible today. One region of present-day Florida is the Central Highlands, an area between the Suwannee River and the St. Johns River that extends about 250 miles (400 kilometers) from the Georgia border south through the center of the state to the area of Arcadia and Sebring.

The sandhills habitat occurs on well-drained sand ridges such as the Lake Wales, Orlando, and Mt. Dora ridges. The vegetation mix of plant species depends on factors such as elevation and fire frequency. In the absence of fire and human disturbance a mixed hardwood forest of Turkey, Bluejack, and Sand Post oaks will develop. After a fire these hardwood species are likely to be replaced by Longleaf pines.

The Central Highlands region of sandy upland ridges is also dotted with thousands of lakes. The lakes and rivers originate in the hundreds of springs in the region. The springs themselves are outpourings from the great Floridan Aquifer, which comes to the surface through openings in the limestone rock. The karst topography of the region creates much of the beautiful scenery.

The central and southern portion of the Central Highlands is home to most of Florida's citrus industry. Citrus production was first introduced by Spaniards during the 16th century, and has become a mainstay of the Florida economy. Both climate and geology contribute to this Florida industry.

 
 

Tracking Eastern Diamondbacks

by Steve Bennett, South Carolina Separtment of Natural Resources

coiled diamondback

The transmitter signal grew stronger with every step we took—beep, beep, BEEP! Somewhere close by, in the low bushes surrounding our feet, was a five and a half foot eastern diamondback rattlesnake. We swept our feet slowly through the brush, confident in the snake chaps that protected our legs. Our eyes scanned the ground deliberately, back and forth, side to side, as we attempted to locate the large snake, but our efforts were in vain. You might think a huge, thick-bodied, boldly patterned rattlesnake lying in open woods would be obvious, but you would be wrong. We moved on.

It was early in our research project and we were learning as much about tracking snakes using radiotelemetry as we were about the snakes themselves. The small radiotransmitters, surgically implanted in the rattlesnakes two weeks earlier, would eventually provide us with insight into the life history of the eastern diamondback, but first we had to master the art of the chase.

As we moved slowly along what must have been a deer trail the signal began to fade slightly. Within a few feet the signal was much weaker and we knew we had already passed by the animal. Backtracking we began to triangulate, taking readings from different compass points, and following the lines to their point of intersection. Finally, after fifteen minutes or more of intense searching we found him ... five and a half feet of rattlesnake in a tight coil the size of a frisbee tucked under a small blueberry bush. As we marveled at the snakes camouflage it became obvious that each of us had stepped within two to three feet of this cryptic predator during our hunt for its location.

closeup of head

The eastern diamondback rattlesnake is the largest venomous snake in North America. The record for this species is eight feet, and even today individuals in the range of five and a half to six feet are still found. The eastern diamondback is a marvelous example of adaptation. The species, like many of its relatives, is a pit viper. Small openings in the snake’s face, located between the eyes and the nostrils, are known as facial pits. These organs allow the rattlesnake to detect minute changes in infrared radiation, the heat produced by living mammals for example, at quite some distance.

The facial pits, envenomation system (venom and fangs) and the large head and body size afford this animal the perfect equipment for life as an ambush predator. The eastern diamondback rattlesnake sits and waits for food to come to it. Tucked under a low shrub or large clump of wiregrass, the rattlesnake sits motionless near a rodent or rabbit trail. The advance of a potential meal registers in the facial pits and when the unlucky rat or rabbit is close enough the snake strikes, quickly.

The prey may stagger off some distance, but succumbs quickly to the venom, and the snake tracks it using another specialized piece of equipment, its Jacobsen’s organ. Located in the roof of the snake’s mouth this organ is linked to the olfactory nerve (sense of smell) and works with the snakes tongue, who’s constant flicking in and out is actually supplying scent molecules to the Jacobsen’s organ.

Eastern diamondbacks prefer large food items, rabbits, squirrels and cotton rats, and they are well equipped for dealing with them. The jaws of all snakes are hinged, allowing them to eat prey items which are large and their skin stretches easily to accommodate the bulk of a big meal. There is another problem, however, associated with eating big things and that is digesting them. This is where the venom of pit vipers plays a dual role.

Pit viper venom is a complex mixture of chemicals, but some of the main components are digestive enzymes. By injecting a large amount of venom into a prey animal the rattlesnake not only subdues it, but also begins the digestive process internally. This is very important if you are going to eat big things, because undigested food in an animals stomach can actually rot and poison the animal that ate it. Digesting your food from the inside out as well as the outside in helps keep that from happening in a rattlesnake's stomach.

diamondback

Rattlesnakes are "cold-blooded", as are all reptiles and therefore have a very slow metabolism. Couple this with their preference for large food items and what you get is an animal that does not eat very often. And this is one of the keys to the life history of the eastern diamondback rattlesnake. Those of us who study the animal feel that two to three big meals each year may be enough to sustain a rattlesnake and a snake that eats five or six meals is having a great year.

Ambush season might be a good name for the active part of a rattlesnakes year, but this only accounts for about six or seven months out of a snakes year. A typical year in the life of an eastern diamondback rattlesnake would end and begin in the same place, a stump hole, gopher tortoise burrow or some other underground structure. The rattlesnake must escape cold weather by taking shelter underground, especially in the northern part of its range. As the weather cools in October and November rattlesnake begin the search for a suitable stump hole or burrow. They may switch sites a few times during the winter months, particularly if the weather warms a bit, and on very warm winter days they might even bask (soak up heat and ultra-violet radiation from the sun) just outside their winter refuge.

diamondback

As winter turns to early spring rattlesnakes begin basking more frequently, even moving a few yards from their stump hole to a choice spot, and may even remain on the surface if overnight temperatures do not drop too low. This goes on for about a month or so, and then when all the conditions are right a rattlesnake will make its first feeding move, to an ambush site. For the next six or seven months the snake will remain on the surface, going underground very seldom when it needs to shed its old skin, digest a meal or perhaps to escape the blistering heat of a dry summer.

During the ambush season a rattlesnake may move great distances, sometimes one or two hundred yards in a day, to find a new ambush site. Over an entire season a snake might move a total of a mile or two in search of ambush sites and food. Typically a snake spends a few days at each ambush site, sometimes moving a few yards one way or the other, but staying in the same general area. One snake we tracked spent over thirty days in an area the size of a small backyard, others have moved more often and over greater distances.

Two of the many things we have learned from our rattlesnake study are that the snakes are excellent at concealing themselves and when concealed in ambush posture they are very reluctant to announce their presence. The snake we walked so close to on that day early in the study is a great example, and was a predictor of things to come. He allowed five people to walk within two to three feet of him and he did not even rattle, much less go into defensive posture and try to strike. Something, perhaps the heavy vibration of our footsteps or the size of our infrared signal told this snake that we were not food, and perhaps we represented danger. His response, like essentially every snake we have tracked since, was to lie still, motionless and quiet and let us walks past. In four years of tracking over twenty rattlesnakes almost daily we have never been rattled at while a snake was in ambush posture. The only other behavior we have encountered at these times occurred when we disturbed the snake too much. At these times the snake would begin to crawl away so slowly as to be almost imperceptible, headed for a nearby underground escape. Wade Kalinowsky, the rattlesnake project’s field manager, has dubbed this behavior the "cryptic crawl", a very apt name.

longleaf pine and turkey oak
Longleaf / turkey oak habitat

The ambush season is interrupted briefly during August and early September, as this is both mating and birthing season for the eastern diamondback rattlesnake. These snakes are biennial breeders, which means that they mate one year and give birth the next, so they produce young every other year, in the best of times. During August female rattlesnakes slow down their movements and wait for males to find them. The males are most likely following scent trails laid down by females that are ready to mate. Females that are pregnant also slow down at this time, and sometime in late August or early September they give birth to live young, anywhere from six or seven up to as many as twenty.

Baby rattlesnakes are born fully formed and ready to go, and there is no apparent parental care. Babies stay near the birth site, typically a stump hole of burrow of some sort, until they shed their first skin. After shedding they leave the birth site, and probably begin to look for their first meal. Not much is know about the young rattlesnakes; we do believe that they spend their first two or three years underground, safe from potential predators such as hawks. Rodent burrows can provide these young animals with protection and a meal.

As the days shorten and cool adult rattlesnakes begin to look for a place to spend the winter. Some return to the previous winter’s stump hole or burrow, some at least come to the same general area, and others find a completely new place to spend the winter. As nights cool considerably the snakes spend more and more time underground, awaiting the warmth of spring to trigger their emergence and the beginning of a new ambush season.

During our study we have been fortunate to follow many eastern diamondback rattlesnakes, and learn many things about their behavior and life history. One of the reasons we wanted to study the eastern diamondback is our concern over the future of this species. Diamondbacks are believed to be declining throughout their range and there are several causes for this. The eastern diamondback is closely associated with coastal habitat, where beach resort development occurs and with the longleaf pine ecosystem, which has declined severely since we settled this country. Habitat loss and alteration, however is only part of the problem. The diamondback has also been a target for those who collect snakes for profit, rattlesnake round-ups, and hobbyists. The third part of the triple whammy is indiscriminate killing. Most people feel compelled to kill any snake, and especially if the snake is a rattlesnake. All three of these factors, habitat loss, over-exploitation and indiscriminate have combined to present an unsure future for the eastern diamondback rattlesnake.

southeastern distribution

One outcome of our study will be to try and educate people about the rattlesnake and its plight. We do know that these animals are potentially dangerous, but we feel this danger has been greatly exaggerated. Our experiences with this species indicate that it is reluctant to confront humans, doing so typically when it is surprised while moving from ambush site to ambush site. Even then, when they do tend to get annoyed, coiling and rattling in defensive display, they typically are also trying to back away from the person who startled them. It is in the best interest of the rattlesnake, for many reasons, not to attack human beings, and this is what I have come to expect from them. They are like most other animals, when left alone, they choose the path of least resistance, fleeing down a hole to escape from disturbance rather than confronting it.

The last thing my colleagues and I, who both study and admire the eastern diamondback rattlesnake, want to see is someone injured by a rattlesnake. We do believe that if folks who wander into rattlesnake territory will follow a few simple rules they can reduce the risk of this greatly. First always walks on trails where you can see in front of you for a good distance. Do not leave trails and walk through low brush or thick grass during the warm months of the year. If you do have to leave the trail wear some sort of protective legging, they are inexpensive and easily obtained at an outdoor supply. If you see a rattlesnake before it sees you stop and watch which way it crawls, let it get well out of the way before you proceed, or double back and take another trail. If you startle a rattlesnake, freeze and after a moment slowly, very slowly back away from the animal.

The chances of anyone encountering a rattlesnake in the wild are small to begin with. If you follow these simple rules there should be no reason to fear the possibility of such an encounter. Then, of course, there is the chance that an encounter with a magnificent predator such as the eastern diamondback rattlesnake will be one of those moments when you are in awe of the beauty and magnificence of this amazing animal ... in such a case you might be a future herpetologist in the making.

>Eastern Diamondback Fact Sheet

 
 
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