Species Description
Eastern Diamond-backed Rattlesnakes are large, heavy-bodied snakes with broad heads and a prominent rattle at the end of the tail. There are infrared-sensitive pits on each side of the head, located between the eye and nostril.
Eastern Diamond-backed Rattlesnakes are the largest rattlesnakes in the world with adults typically measuring 110 to 180 centimeters in total length but may reach a maximum length of around 250 cm. They are sexually dimorphic in size, with males attaining greater lengths by about 20 percent and having longer tails than females. Eastern Diamond-backed Rattlesnakes are named for the 24 to 35 dark-brown to black diamond-shaped markings that run down the back. The diamonds, which are light in the center and bordered by yellow, typically fade into three to six dark bands near the tail. The dorsal background color ranges from platinum silver to nearly black but is typically a shade of brown. A dark brown to black stripe, bordered by two white or cream colored stripes, runs from the eye to the corner of the mouth. The dorsal scales are heavily keeled with 25 to 31 scale rows at midbody. Ventral scales number 159 to 187 and are cream colored. Juveniles resemble adults in color and pattern and are 30 to 46 cm. in length at birth.
Their prominent rattle is composed of loosely-articulated segments of keratin that make a buzzing sound when shaken, and a new segment is added to the rattle each time a snake sheds its skin. The rattle is used as a warning to potential predators.
Taxonomy
The scientific name of the Eastern Diamond-backed Rattlesnakes is Crotalus adamanteus. The epithet adamanteus means diamond-shaped, and refers to the dorsal pattern of the species.
Distribution
Eastern Diamond-backed Rattlesnakes are restricted to the Coastal Plain of the southeastern United States. They historically ranged from extreme eastern Louisiana to southeastern North Carolina and south through all of Florida. Although they can still be locally common these rattlesnakes are experiencing significant population declines throughout their range. Anthropogenic factors such as habitat loss, fragmentation and alteration, and wanton killings are cited as the primary causes of the declines. Currently they are now nearly extirpated from Louisiana, considered endangered in North Carolina and rare in Mississippi, Alabama and South Carolina.
Habitat
Eastern Diamond-backed Rattlesnakes occur in a variety of habitats including swamp forests, xeric hammocks, tropical hammocks, oak scrubs, temperate hardwood forests, salt marshes and coastal dunes, but they are most often associated with open canopy pine savannas. A positive correlation has been found between Eastern Diamond-backed Rattlesnakes and large tracts of land, suggesting that habitat fragmentation affects the distribution of these rattlesnakes. Eastern Diamond-backed Rattlesnakes may also be common in coastal areas and on undeveloped barrier islands within their range. Their ability to swim allows them to colonize offshore islands, and they have been documented miles off of the coast in the ocean.
Suitable overwintering shelters are an important habitat component throughout the range of Eastern Diamond-backed Rattlesnakes except in extreme southern Florida. Burrows of Gopher Tortoise (Gopherus polyphemus) and the Nine-banded Armadillo (Dasypus novemcinctus), as well as small mammal and crab burrows, are commonly used overwintering shelters. Other commonly used shelters are stump holes, root systems of wind-fallen trees, rotting logs and cavities under the roots of saw palmettos. These shelters are also important for escaping the heat of the summer, avoiding fire, and using as birthing sites.
Movement and Home Range
Reported home range size estimates of Eastern Diamond-backed Rattlesnakes from radio telemetry studies vary greatly between individuals, sexes, regions and years. Home range estimates (100% minimum convex polygon, MCP) from Tall Timbers reserve in the Redhills region of northwestern Florida were 242 ha. for males and 80 ha. for females. In north Florida the average home range (MCP) of males (N=4) was 84.3 ha, and the average home range of non-gravid females (N=2) was 46.5 ha. (Timmerman, 1995). The average home range size (MCP/95% fixed kernels) estimated in southern Mississippi was 74.1/79.4 ha. for males and 15.7/11.7 ha. for females. In South Carolina the average home range (95% fixed kernels) was 82.82 ha. for males, 28.6 ha. for non-gravid females, and 18.1 ha. for gravid females. Home range estimates (MCP) from southwestern Georgia were 30.49 ha. for males and 20.59 ha. for non-gravid females. Eastern Diamond-backed Rattlesnakes are solitary animals but the overlapping of home ranges of both males and females suggests that they are not territorial.
Eastern Diamond-backed Rattlesnakes occupy relatively stable home ranges, using the same general area year to year, and they may even return to some of the same feeding or overwintering locations throughout a year or in successive years. In some habitats, there are no seasonal shifts in habitat use by Eastern Diamond-backed Rattlesnakes while in others they will overwinter in Gopher Tortoise burrows located on sand ridges or knolls and move to a more prey-rich environment for foraging. Average distance traveled in telemetry studies were highest in the fall months, presumably related to mating, and average distances traveled is lowest in winter. Movements are primarily diurnal, and nocturnal activity is rare and seems to be restricted to the hot summer months.
Diet
Feeding typically takes place from spring through fall but occurs year round in southern Florida. Winter feeding occurs rarely in the northern part of the range of Eastern Diamond-backed Rattlesnakes. Eastern Diamond-backed Rattlesnakes are an ambush predator that hunts from a tight ambush coil. Rattlesnakes use their tongue and vomeronasal system to pick up chemical cues from the environment in order to locate suitable ambush site, which are often trails frequently used by rodents. When a prey item passes, the rattlesnake can detect it with its infrared sensitive pits located between their eyes and nostrils. When the prey is within range, it is struck, envenomated and released. The prey then runs off until it succumbs to the effects of the venom. Chemical cues are deposited on or in the prey’s body during the strike, and the rattlesnake again uses it vomeronasal system to track down the prey item. Eastern Diamond-backed Rattlesnakes, like other sit-and-wait predators, have low standard metabolic rates (SMR). This allows them to conserve energy and go substantial lengths of times between feedings.
Eastern Diamond-backed Rattlesnakes feed primarily on small mammals, although birds are occasionally taken, as well. Rabbits (Sylvilagus sp.) and Cotton Rats (Sigmodon hispidus) are the most common prey items. Other prey items include the cotton mouse (Peromyscus gossypinus), Florida wood rat (Neotoma floridana), black rat (Rattus rattus), gray squirrel (Sciurus carolinensis), bobwhite quail (Colinus virginianus), eastern meadowlark (Sturnella magna) and raccoon (Procyon lotor).
Reproduction
Eastern Diamond-backed Rattlesnakes are reproductive as early as three to four years or possibly as late as seven to eight years of age, and females can reproduce every two to four years in the wild. The mating season occurs from late summer through fall, beginning in August in the northern part of their range and may last until December in southern Florida. Spring mating has occasionally been reported. During this period, adult males make longer movements searching for receptive females. Although not strictly territorial outside of the breeding season, males during breeding season may engage in ritualized combat over the rights to a receptive female. This combat consists of both snakes raising the anterior portions of their body off the ground and attempting to pin the other snake to the ground. During combat the snakes never attempt to bite one another. Combat may last from a few minutes to a few hours, until the losing male flees the area.
The gestation period typically lasts 90 to 120 days. During the gestation period females will not feed, and one to two months prior to parturition, they will move to a natal shelter. Logs, stump holes, windblown trees and burrows of the Gopher Tortoise and Armadillos are common natal shelter sites. With many species of rattlesnakes, natal sites provide an important thermal gradient that allows the female to regulate her body temperature during pregnancy.
Eastern Diamond-backed Rattlesnakes give birth to live young (ovoviviporus), with birthing taking place from late July through early October. Clutch sizes from four to 32 have been documented with an average clutch size around 14. After birth, the mother and newborn snakes will stay together at the natal shelter until the newborns shed their skin for the first time. This natal shed typically occurs seven to ten days after birth. After the natal shed, all of the snakes will disperse.
Conservation Concerns
Eastern Diamond-backed Rattlesnakes are one of the top predators in the southeastern Coastal Plain of the United States. They help to control rodent populations, which may carry harmful diseases and are also vectors for parasites such as fleas and ticks which can also carry harmful pathogens.
The causes for decline in Eastern Diamond-backed Rattlesnake populations are primarily anthropogenic. Habitat loss and degradation, human persecution, road mortality and exotic species are the major threats to this species.