timber rattlesnakes

The timber rattlesnake

Order: Squamata
Subfamily: Serpentes
Family: Viperidae
Subfamily: Crotalinae
Scientific name: Crotalus horridus



Description: The timber rattlesnake, also known as the canebrake or broad banded rattlesnake is a fairly heavy bodied snake that may range in length from 3 to 5 feet.  As a member of family viperidae it has an elliptical pupil and a very distinct arrow shaped head that occurs as a result of the large venom glands located behind the eye.  The top of the head is covered by many small scales which can distinguish it from rattlesnakes in genus Sistrurus which overlap in its range.  It also has a dark stripe running at an angle from eye to jaw, a set of lorial pits located between the eye and nostril (a characteristic of all members of sub family crotalinae) and heavily keeled scales.  The adult pattern and coloration is quite variable, but generally consists of a dark brown to tan or grey dorsal color with dark crossbands that often blend into a very dark or black tail.  Melanism is also seen in the Timber rattlesnakes and it is not uncommon to see individuals that have very dark coloration or are completely black.  The sex of an individual may be determined by the number of subcaudal scales, females having 18-20 subcaudal scales while males have 21 or more subcaudal scales.

Distribution and Habitat: The timber rattlesnake ranges across much of the eastern United States, from northern Florida up to New Hampshire and west to east Texas and southern Minnesota.  Despite this large range, populations are often sparse and isolated as a result of human encroachment.



Timber rattlesnakes are woodland dwelling species that can be found in deciduous and coniferous hardwood forests.  They prefer rocky, uneven terrain and will often make use of crevices in cliffs and ledges.  Gravid females are especially known to spend time on  exposed rock ledges absorbing extra heat and have been known to gather there in numbers.  Timber rattlesnakes are migratory, traveling to a particular winter den in the autumn and then radiating outward from that den in the spring.



Diet and Feeding Strategies: Timber rattlesnakes feed primarily on small mammals such as mice, rats, squirrels, chipmunks and voles but if given the opportunity they will also prey upon small to medium sized birds, lizards, amphibians and rarely other snake species.

Timber rattlesnakes are sit-and-wait ambush predators whichlocate and target prey using visual, chemosensative and thermosensative mechanisms.  They subdue their prey using complex hemotoxic and myotoxic venom.  However, venom composition may vary considerably both ontogenetically and geographically.  An example of this is the Type A venom composition which is found primarily in the southern populations and posses a particularly strong phospholipase A2 which acts as a neurotoxic component.  As a result, Type A venom has a much lower LD50 value (.92 mg/kg) than the LD50 values of northern populations (6.32 mg/kg).

Reproduction: Timber rattlesnakes reach sexual maturity between 4 and 8 years, with males becoming sexually mature earlier (4-5 years) than females (6-8 years).  Males seek out the females following pheromone trails that females release during their midsummer shed. Males are also known to engage in mating combat, though these fights are non-violent pushing matches that rarely result in injury.  Females typically reproduce once every 2-4 years with litters that range between 5 and 22 young.  Timber rattlesnakes are ovivipiparous and the young are born with fully functional fangs and venom.




Longevity and Conservation Status: Timber rattlesnakes generally live approximately 20 years in their natural habitat, though captive specimen have been recorded living over 35 years.   Timber rattlesnakes are listed as threatened by the IUCN, and are classified as under “least concern,” but they are listed as endangered in several states including Ohio, New Hampshire, New Jersey, Connecticut and others.  The major threats to extant populations are habitat destruction, organized and market snake hunting and road mortality.


Personal Experience: My encounters with the timber rattlesnake have occurred on the eastern side of Pennsylvania, primarily in Lehigh Valley Gorge state park in Jim Thorpe where there is pristine habitat and a healthy population.  The snakes blend into their environments extremely well so they are difficult to spot and they often may only have a single coil exposed to absorb heat.  All of the timber rattlesnakes that I have encountered have been extremely well-tempered and unaggressive.  If spotted they generally make an effort to flee as opposed to striking.  They are a beautiful species to see in the wild, particularly dark phase or melanistic individuals whose scales often have a velvety appearance.

 

Links: for more information- http://www.iucnredlist.org/apps/redlist/details/64318/0
http://www.fs.fed.us/database/feis/animals/reptile/crho/all.html
http://www.dec.ny.gov/animals/7147.html
http://www.oplin.org/snake/fact%20pages/rattlesnake_timber/rattlesnake_timber.html
http://www.timberrattlesnake.net/
http://www.dnr.state.oh.us/Home/species_a_to_z/SpeciesGuideIndex/timberrattlesnake/tabid/6777/Default.aspx
http://www.ntrc.tamuk.edu/Snakebook/display_species.php?Scientific=Crotalus%20horridus