Species: Crotalus oreganus

Western Rattlesnake

Species

Encyclopedia of Puget Sound

Western rattlesnakes have a horny rattle or button on the end of the tail, numerous small scales on the top of the head, a head that is much broader than the neck; and an infrared sensing pit on each side of the face between (but lower than) the eye and nostril. Coloration is highly variable, ranging from light tan or pink to black, usually with large blotches along the back and sides and bands around the tail. Usually a light stripe extends from behind the eye to the corner of the mouth. The scales on the back and sides are keeled. THe pupilof the eye is vertically elongate in bright light (like a cat's eye). These snakes rarely exceed 3.3 feet in total length. In eastern Utah, southwestern Wyoming, and west-central and southwestern Colorado, adults rarely exceed 26 inches (65 cm). Newborn young are about 7-9 inches (18-24 cm) in total length. Primary source: Hammerson (1999).

Classification

Kingdom

Animalia

Phylum

Craniata

Class

Reptilia

Order

Squamata

Family

Viperidae

Genus

Crotalus

NatureServe

Source:
ELEMENT_GLOBAL.2.104250

Classification

Other Global Common Names

crotale de l'Ouest

Informal Taxonomy

Animals, Vertebrates - Reptiles - Snakes

Formal Taxonomy

Animalia - Craniata - Reptilia - Squamata - Viperidae - Crotalus - in New Mexico (Glenn and Straight 1990).

Ecology and Life History

Migration

false - false - false - Gravid females tend to be more sedentary than nongravid individuals. In southern British Columbia, gravid females were sedentary and usually stayed within 50-100 m of the winter den (Macartney 1989).

Non-migrant

false

Locally Migrant

false

Food Comments

Diet includes mainly small mammals; also birds, lizards, and rarely amphibians (see Ernst 1992). See Diller and Johnson (1988) for predation rate on small mammals in southwestern Idaho. In British Columbia, gravid females generally did not feed (Macartney and Gregory 1988, Macartney 1989); feeding by gravid females has been observed in some areas (e.g., Idaho, Wallace and Diller, 1990, J. Herpetol. 24:246-253). Juveniles in some regions prey mostly on lizards rather than on small mammals.

Reproduction Comments

Mating occurs mostly from mid-summer to early fall, occasionally in spring. Young are born August-October (September-early October in Idaho). Litter size increases with female size (average 5 in small subspecies, maximum about 25 in the largest females of the largest subspecies). Individual adult females may not give birth in some years, probably depending on nutritional status; interval between litters was 2 or more years in British Columbia (Macartney and Gregory 1988), probably 2-3 years in southwestern Wyoming (Ashton and Patton 2001); some females from northern Idaho reproduce in consecutive years. In southwestern Idaho, females often gave birth biennially (Diller and Wallace 1996). Individuals require several years (4-6 years in Idaho, 5-7 years [females] in British Columbia) to reach sexual maturity in areas with a short growing season (Macartney and Gregory 1988). Pregnant females may congregate in a small area.

Ecology Comments

Mortality tends to be high in first-year young. May congregate at hibernation dens; formerly many den sites harbored up to several hundred snakes, but most of these populations have been decimated by humans. Primary predators include humans, various mammalian carnivores, raptors, kingsnakes, whipsnakes, and racers. The sound emitted from a vibrating rattle is fairly loud and may continue uninterrupted for several minutes in an aroused, fully warmed rattlesnakesnake. Burrowing owls and gophers snakes, which often share mammal burrows with rattlesnakes, produce hissing vocalizations that sound very much like the rattling of a rattlesnake.

Conservation Status

NatureServe Global Status Rank

Global Status Last Reviewed

2006-08-29

Global Status Last Changed

2001-12-13

Distribution

Conservation Status Map

Global Range

G - 200,000-2,500,000 square km (about 80,000-1,000,000 square miles) - G - This species, recently separated from Crotalus viridis, ranges from southern British Columbia to central Baja California, and east to the Rocky Mountains (Pook et al. 2000), Ashton and de Queiroz 2001, Douglas et al. 2002). The ranges and relationships of Crotalus oreganus and Crotalus viridis in the Four Corners region and in northwestern Colorado have not been precisely defined and need further clarification (Hammerson 1999; Brennan and Holycross, 2004, Herpetol. Rev. 35:190-191). Elevational range extends from sea level to around 3,355 meters (11,000 feet) but most localities are below 2,745 meters (9,000 feet) (Basey 1976, Stebbins 2003, Campbell and Lamar 2004).

Global Range Code

Global Range Description

200,000-2,500,000 square km (about 80,000-1,000,000 square miles)

ELEMENT_GLOBAL.2.104250