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Canadian Herpetological Society Société d'Herpétologie du Canada |
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Western Rattlesnake
Crotalus oreganus
Family: Viperidae
The subspecies of Western Rattlesnake that occurs in Canada is the Northern Pacific Rattlesnake (Crotalus oreganus oreganus).
COSEWIC status:- Threatened
- Threatened
- Least Concern
Description
The Western Rattlesnake is a moderately large, heavy-bodied snake that can reach adult lengths of 1.6 m. It has a distinctly triangular head, heat-sensing pits, vertical pupils and usually a rattle at the end of the blunt tail. The body colour is tan, brown, olive or grey with dark brown dorsal blotches that turn into banding near the tail and smaller blotches along the sides. The blotches are often lighter in the centre, dark at the edges and surrounded with a light whitish-yellow border.
Similar Species
Although there are no other rattlesnake species in British Columbia, there are other blotched snakes which are commonly mistaken for rattlesnakes. The Great Basin Gophersnake has round pupils and the tail tapers to a fine point. Desert Nightsnakes also have vertical pupils but are much smaller and more slender than Western Rattlesnakes. Neither of these species has the typical triangular head or rattle of a rattlesnake.
Distribution
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The Canadian distribution of the Western Rattlesnakes is limited to a small number of mountain valleys in interior British Columbia. The various sub-species of Western Rattlesnake occur throughout the western U.S. and onto the Baja California Peninsula in northwestern Mexico.
Habitat
In Canada, Western Rattlesnakes spend the active season (April to September) in river valleys and foothills where they inhabit arid habitats, including desert, grasslands, sagebrush-dominated scrubland, woodlands and rocky habitats. In the fall, the rattlesnakes hibernate communally in talus slopes and rock crevices on south-facing slopes, although some individuals may overwinter in mammal burrows. Cover objects, such as rocks, low-lying vegetation and dead wood, are important microhabitat features. Open habitats with adequate cover and retreat sites are used for gestation, and they are typically within close proximity to hibernacula.
Biology
Females begin breeding at an age of four to seven years and reproduce every one to three years; males reach maturity in three to four years. Individuals of this species may live for as long as 30 years. Mating generally occurs in the late summer and an average of 10 live young are born in late summer of the following year. Western Rattlesnakes are most active in the morning and afternoons, but in hot weather they may shift to nocturnal behaviour. Western Rattlesnakes primarily eat small mammals and, like all rattlesnakes, they have heat sensing facial pits which allow them to locate their warm-blooded prey. Rattlesnakes have venom, which they use to subdue their prey. They will also eat birds, lizards, frogs and other snakes. Since they prey largely on small mammals, rattlesnake populations help to control rodents and other pests and are an asset to farming communities. In spring and fall they can be found basking, often in high abundance, at the entrance to their hibernacula. Their primary defensive strategies are to rely on their cryptic camouflage to remain hidden, retreat into a nearby retreat site or rattle to warn other animals to keep away; they generally bite only as a last resort. Anyone who is bitten by a rattlesnake should seek medical assistance.
Threats
This species is restricted to a small number of mountain valleys where natural habitats are being rapidly converted into agricultural and urban uses. Consequently, this habitat loss poses a very serious risk to Canadian populations of Western Rattlesnake. Increased rates of road mortality parallel rates of habitat loss as more roads are built throughout the mountain valleys and human population increases. Rates of road mortality can be especially high in areas where roads bisect hibernacula and summer habitat. Unfortunately, human persecution by misinformed individuals continues to be a threat to this species, despite its status as a species at risk and the legal implications of killing them.