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The Cold Blooded NewsThe Newsletter of the Colorado Herpetological SocietyVolume 28, Number 7; July, 2001 |
Habitat:
An occupant of a variety of habitats, Crotalus atrox is a habitat generalist, and can be found in grasslands, scrub oak-juniper forest, thorn scrub, rocky canyons and out-croppings, and deserts. Trash piles and junk yards can often provide refuge for many vermin such as rats and mice. Sites such as these in rural settings may attract rattlesnakes and other snakes as well.
Distribution:
Western diamondback rattlesnakes range from western Arkansas westward through eastern and south-central Oklahoma, Texas (except the extreme east and northern panhandle), central and southern New Mexico and Arizona, possibly extreme southern Nevada, southern California, and southward into Mexico to extreme northeastern Baja California and northern Sinaloa in the west, and northern Veracruz, Hidalgo and Queretaro in the east. Most of its range lies below 1,500 m (Ernst, 1992). However, in San Luis Potosi, Mexico this species has been found at elevation of 2,438 m (Werler and Dixon, 2000).
Activity:
The activity patterns of the western diamondback rattlesnake is similar to many other snakes. C. atrox has been noted to be active as early as March 9 (Minton, 1958). In 1998 I found specimens at night while crossing the road in Cameron, Hidalgo, and Willacy counties in south Texas as late as December 23. Like other reptiles, the activity of C. atrox is largely influenced by temperature. This is evident during the various seasons. During the spring months of April to May when mild temperatures prevail, these snakes are active during the day. Their diurnal activities come to a halt in June through August during the oppressive heat of the summer. During these months, activity is largely limited to early mornings and late evenings when there is some relief from the heat. The cooler temperatures of September seem to also entice some specimens into diurnal activity. However, this activity is not as prevalent as that during the spring.
A communal den site is used for shelter during the winter. Den sites are typically found within southerly facing rocky outcroppings. The winter dormancy may be periodically interrupted during periods of warm weather. This was evident during a night drive in Llano county in mid-November of 1998 as a small male specimen was found crossing the road at night. The ambient air temperature at the time of the sighting was 48-50 Fahrenheit. Denning is also advantageous as there is a good chance of males mating with females as they leave the hibernacula.
Size:
It is not uncommon at all to be regaled with tales of "giant 6-7 footers crossin' th' road" from many south Texas ranchers. In fact there are several documented cases of specimens from Willacy and Hidalgo counties measuring well over six feet in total length. However, many snakes bodies are stretched or left hanging for considerable lengths of time; this can add as much as 20% to the total body length.
Amazingly, there are specimens measuring over five feet in overall length occasionally found in Cedar Hill State Park (near Dallas). Even specimens of this size are awesome in their appearance and command respect from even the most seasoned herpetologist.
Description:
Western diamondback rattlesnakes do display some degree of polymorphism in their basal coloration. This of course is due to genetic expression from different populations. The basal color can range from brick red, buff pink, straw-yellow, beige, and light gray. Boldly marked chevrons form an interlacing rhombic diamond-like pattern down the middle of the snake's back, thus affording this species its common name. Often these markings are outlined in black and white. The head is broad and two white diagonal lines are present on either side of the eye extending to the supralabial scales.
Another common name used in reference to this species is "coon-tail rattler". This moniker is derived from the white tail with encircling black bands. Although some specimens bear different colors no subspecies are recognized. While crossing the road, rattlesnakes are known to hold their head and tail up at roughly a 45 degree angle. Although this may not always be the case, it is a useful means to help identify a snake as a rattlesnake at considerable distances.
Similar Non-Venomous Species:
Possibly the most crucial component for positively identifying a snake as a rattlesnake is the presence of a rattle. This may seem as quite an elementary component, yet I am compelled to include this feature as many inexperienced people confuse ratsnakes (Elaphe sp.) and bullsnakes (Pituophis sp.) for rattlesnakes. When alarmed, either species will rapidly vibrate their tails. Should the vibrating tail contact loose leaves or dried vegetation the sound becomes more closely identifiable with that of a rattlesnake.
The best imitation of a rattlesnake by a non-venomous species is that which is performed by the bullsnake {Pituophis melanoleucus sayi) . These large and heavy bodied serpents share their range and habitat with rattlesnakes. Bullsnakes will also vibrate their tails, yet their talent for creating sound while forcefully expelling air is the most convincing. In many specimens, this noise does resemble the sound of a rattlesnake so closely that the two species can be difficult to differentiate on sound alone.
Reproduction:
Of the two sexes, males are the larger. During the spring males are known to engage in ritualistic combat. The two contestants often engage in this behavior under the attention of a nearby female. The males intertwine the anterior portions of their bodies while spiraling upward. The victor is determined as the male who forces his opponent to the ground. This spiraling demonstration often results in both snakes toppling over and continuing to wrestle on the ground.
Alas, to the victor goes the spoils. The winner of these "wrestling matches" often receives mating privileges with the nearby female. Courtship involves the male actively tongue flicking the dorsal surface of the female's body. As the courtship ensues, the male's head begins to move to and fro in a jerky yet rhythmic motion. Soon after this activity, the male will align his cloaca with the female's. Should his intentions be undesired, the female will "shove" the male aside by using an arch of her coils. In late September to early October, females will give birth to 9 to 14 young typically measuring 9 to 13.5 inches (Tennant, 1998). In some populations, females only reproduce every other year.
Diet:
Western diamondback rattlesnakes prey chiefly upon mammals such as mice, rats, cottontail rabbits, chipmunks, and squirrels. C. atrox will actively forage for prey as well as resort to ambush tactics. When in ambush, C. atrox usually lies quietly beside a frequently used rodent trail. At such times it may lay a coil over its rattle, perhaps to muffle it (Thayer, 1988).
Obviously, this species can be of great benefit to man by consuming destructive rodents. Rodents that are known to carry the plague and hantavirus are known to exist in the western United States. These life threatening illnesses are additional reasons why this snake should be left alone to its affairs of hunting rodents.
Conclusion:
The western diamondback rattlesnake is the most widespread venomous snake in the state of Texas. It is a highly popular species in zoological displays across North America and Europe. Although its venom is quite potent few deaths are reported and medical attention can result in a positive outcome for the bite victim.
Literature Cited:
Ernst, C. H. 1992. Venomous Reptiles of North America. Smithsonian Institution Press, Washington and London, 236pp.
Minton, S. A., Jr. 1958. Observations on amphibians and reptiles of the Big Bend Region of Texas. Southwestern Naturalist 3:28-54.
Tennant, A. 1998. A Field Guide to Texas Snakes. Gulf Publishing, 291pp.
Thayer, F. D. 1998. Crotalus atrox (Western Diamondback Rattlesnake). Hunting Behavior. Herpetological Review 19:35.
Werler, J. E. and J. R. Dixon. 2000. Texas Snakes. University of Texas Press. Austin, Texas, 437pp.
Cross Timbers Herpetologist, Newsletter of the Dallas-Fort Worth Herpetological Society, Volume 2, Number 1, April 2001.
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