THE TIMBER RATTLESNAKE ALONG THE CONNECTICUT RIVER



For inquiries contact Thomas F. Tyning , Herpetologist, Massachusetts Audubon Society

The timber rattlesnake (Crotalus horridus) was one of the first New World animals to capture the imagination and attention of European explorers and naturalists. Though the 16 genera and 144 species of pit vipers (subfamily Crotalinae, family Viperidae) has a worldwide distribution, several genera, including Crotalus, are strictly New World animals. With their large, recurved fangs (capable of injecting a fairly large amount of venom), wide pre-colonial distribution, and their trademark tail appendage, rattlesnakes were viewed with awe, fascination, and loathing; typically a combination of all three emotions. Things have not changed much in the past three hundred years.

Rattlesnakes are distinct in having a specialized structure at the end of their tail (the rattle) that consists of loosely connected, cornified segments that produce a buzzing sound when the tail is vibrated.

THE RATTLE

Newborn rattlesnakes have a single segment (the button) and the first new segment is added at the initial shedding, typically within ten days of birth. Each successive shedding produces a new rattle segment, while the oldest segments at the tip are occasionally broken and are lost. It is uncommon to find a rattlesnake with more than 10 or 12 rattles and equally rare to find only 1 or 2 segments. Accurate identification of timber rattlesnakes is complicated by the fact that several New England snakes (black racer, milk snake, hognose) vibrate their tails when cornered -- but not all that rattles is a rattlesnake!!

There are about 30 species of rattlesnakes in two genera, Crotalus and Sistrurus, ranging from southern Canada to south-central South America. It is proposed that the center of origin of the Crotalids (the pit vipers), from Viperid (true vipers) stock, was Eurasian which possibly crossed the Bering land bridge in the Paleocene and Eocene and gave rise to the North American Crotalinae shortly thereafter. It is likely that the genus Crotalus is among the most recently evolved of the line. The Crotalinae are noted for the development of loreal or facial pit organs that function to detect infrared radiation, presumably as an adaptation for efficient hunting of prey, detection of potential predators, and perhaps for other functions. Currently only a single subspecies of timber rattlesnake is recognized by some researchers, while many distinguish the southeastern coastal plain canebrake rattlesnake (Crotalus horridus atricaudatus), and others believe a western form should be described. New England is home to the nominate subspecies, the timer rattlesnake, Crotalus horridus horridus.

In general the timber rattlesnake is a variable-patterned species with yellow and black morphs and many intergradations between.

YELLOW MORPH

BLACK MORPH

In colonial times it was believe that males were black and females yellow, though this has been shown to be inaccurate. Albinistic and melanistic individuals are known, though the darkest morphs and most melanistic individuals are not distributed randomly. There are few black morphs west of the Mississippi River, and no melanistic Canebrakes are known. Some researchers suggest that dark-phase individuals prefer mature forests with numerous fallen logs while yellow-phase rattlesnakes are more frequently found in young forests with predominant leaf litter cover. This is possibly a function of background color matching from both would-be prey and predators. Dark morph snakes predominate at higher, cooler, wetter, and more densely forested sites in Shenandoah National Park and in other areas of the Appalachian mountains, especially in the northeast. There is at least one Connecticut River population that appears to have only yellow-morph individuals. Most other locations have a wide mix of color variants.

The distribution of the timber rattlesnake once included 31 states. At the time of European settlement, the eastern subspecies Crotalus h. horridus had a nearly continuous range from New England to northern Georgia with scattered populations in the midwest to southern Ontario. It presently inhabits only 27 states. It has been extirpated from Maine, Rhode Island, central New Hampshire, most of Vermont, Long Island, and eastern and northern Ohio (Martin, 1992), probably from Michigan and Delaware (historic data questionable) and has shrunk from many of its former haunts. Currently, nine states (including all New England states) and the Province of Ontario offer the timber rattlesnake some form of protection, listing it as threatened or endangered, or having a restricted or no-take policy. Fifteen other states have general regulations that protect some or all herpetofauna and therefore the timber rattlesnake by default. There are seven states where the timber rattlesnake receives no protection of any kind. Currently, many populations of timber rattlesnakes survive in isolated, forested mountain areas that are continually isolated from even the nearest populations by habitat fragmentation caused by highways, housing and industrial developments, off-road vehicle traffic, and other factors.

Currently, populations of timber rattlesnakes in many states are believed to be in decline. Collection for pets and malicious killing are the largest problems facing timber rattlesnakes. Bounty hunting, commercial collection, habitat alteration, sport hunting, organized round-ups, and behavioral disturbance are addition factors in the decline of the species. One researcher indicates that 26% of New York den sites are already extinct, another 5% face imminent extinction, while the rest are in various states of depletion. He further states that New York populations have suffered a 60% reduction since 1900 due to a single, active snake collector. This one person is believed to have taken more than 4,000 timber rattlesnakes from New York, Connecticut, and Massachusetts over the past 45 years. The fact that the activities of a single person, no matter how experienced, can have deleterious effects upon many populations of rattlesnakes may seem difficult to believe. But recent efforts to document these activities have shown that many of the estimates of poaching are likely to be conservative. The poacher himself states he has "captured approximately 9,000 rattlesnakes," instead of the 4,000 ascribed to him.

Timber rattlesnakes are long-lived, late-maturing and slow-reproducing animals that have relatively short activity periods during a given year. Our eastern subspecies is a forested, upland rattlesnake, unlike most of the other members of the genus that are either desert or prairie inhabitants. The species is described as a typical K-selected animal characterized by long adult lifespan, low reproductive output, with low turnover in population, making it very susceptible to even low exploitation levels. Individuals in a region congregate at historic overwintering sites and it is here, in concentrated numbers, that they are most vulnerable. Adult males, non-gravid females, and juveniles must migrate each spring and summer to foraging and mating habitats.

MATING BEHAVIOR

In New York, mean maximum migrations were 4.07 km by males and 2.05 km by females. These out-migrations bring the snakes into contact with roads, housing developments, well-used hiking and ORV trails, and potential predators. New Jersey snakes moved in a looping pattern, returning to their wintering site by late autumn. All timber rattlesnakes migrate back to their den areas (showing high fidelity to specific locations) in autumn where they retreat until the following spring. One field researcher estimated the active season ranges from 4.6 months to 7.4 months per year throughout the entire range of C. h. horridus. Gravid female timber rattlesnakes do not migrate far from their dens but seek exposed, well-heated rock outcrops where they bask in the open for most of the summer, often several individuals clustering. This behavior and habitat selection make them especially vulnerable to exploitation. Timber rattlesnakes brought in from 13 separate organized rattlesnake hunts in Pennsylvania between 1985 and 1987 were examined. Almost 84% of the mature females that were captured were gravid, and snake hunters indicated that they specifically searched areas that were rocky and exposed.

Given many aspects of its biology, the current (and suspected increased) demand for trade (pet, sport, leather, trinket), increased habitat alteration, and prevailing attitudes, the future of the eastern timber rattlesnake appears dim. Virtually all field researchers agree that there is a good case to be made for giving the timber rattlesnake total protection throughout its range. The main problem with protection is effective enforcement of existing statutes and unevenness in legal protection range-wide. If even a single state allows timber rattlesnakes to be taken, then the protection afforded in all other states is functionally eliminated. Snakes poached from a protected state are brought to dealers elsewhere and listed as captured in a "legal" state. There is ample evidence of this currently. My opinion is that one of the most effective methods of protecting remaining populations of eastern timber rattlesnakes is to have the subspecies listed under the Federal Endangered Species Act. A group of field biologists is currently attempting to develop state-by-state recovery plans for the timber rattlesnake.

The chance of anyone using the Connecticut River actually seeing a timber rattlesnake is slim to none. Not because they can't swim (they do, and well), but because they prefer to remain in forested habitats, sitting quietly for most of the year, hoping to catch a couple of mice or chipmunks for their summer meals. Many reports of timber rattlesnakes in the immediate vicinity of the river are almost certainly attributed to the common, large-bodied and aquatic water snake (Nerodia sipedon, a non-venomous species that is fascinating in its own life history. But that, of course, is another story.

GENERAL REFERENCES:

Brown, William S. 1993. Biology, status, and management of the timber rattlesnake (Crotalus horridus: a guide for conservation. SSAR Circ. 22. 78 pp.

Brown, Christopher W. and Carl H. Ernst. 1986. A study of variation in eastern timber rattlesnakes, Crotalus horridus. Brimleyana 12:57-74.

Campbell, Jonathan A. and Edmund D. Brodie, Jr. (eds.) 1992. Biology of the Pit Vipers. Selva Press. 467 pp.

Collins, Joseph T. 1990. Standard common and current scientific names for North American amphibians and reptiles. (3rd edition) SSAR Circular No 19. 41 pp.

Conant, R. and J. T. Collins. 1991. Reptiles and Amphibians of Eastern/Central North America. Houghton Mifflin. 450 pp.

Ernst, Carl H. 1992. Venomous Reptiles of North America. Smithsonian Inst. Press. 236 pp.

Martin, W.H. 1992. The timber rattlesnake: its distribution and natural history. pp. 13-22 IN: T. F. Tyning (ed.), Conservation of the Timber Rattlesnake in the Northeast. Massachusetts Audubon Society, Lincoln, MA.

Palmer, Thomas. 1992. Landscape with Reptile. Tichknor and Fields. 340 pp.

Reinert, Howard and Robert T. Zappalorti. 1988. Timber rattlesnakes (Crotalus horridus of the Pine Barrens: their movement patterns and habitat preference. Copeia 1988:974-978.

Stechert, Randy. 1982. Historical depletion of timber rattlesnake colonies in New York State. Bull. New York Herpetol. Soc. 17:23-24.

Tyning, Thomas F. 1990. Conservation of the timber rattlesnake in the Northeast. Massachusetts Audubon Society, Lincoln, MA.

Tyning, Thomas F. 1990. A Guide to Amphibians and Reptiles. Stokes Nature Guides. Little, Brown and Co. 440 pp.