Crotalus oreganus

Common names: western rattlesnake,^[2] northern Pacific rattlesnake,^[3] Pacific rattlesnake,^[4] more.

Crotalus oreganus is a venomous pitviper species found in the western United States. Seven subspecies are currently recognized, including the nominate subspecies described here.^[3]

Additional recommended knowledge

Daily Sensitivity Test

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Essential Laboratory Skills Guide

Description

The size of this species varies greatly, with some populations being stunted and others growing very large. Mainland specimens often reach 100 cm in length, with the largest on record being 162.6 cm (Klauber, 1956).^[2]

This species, in its various forms, shows considerable ontogenetic variation. Juveniles usually have more or less distinct patterns, but this fades as the animals mature. The color of the iris often matches the ground color, which may be bronze, gold, different shades of tan, pink or gray.^[2]

The color pattern of the typical form, C. o. oreganus, has a dark brown, dark gray, and sometimes black or pale yellowish ground color. This is overlaid dorsally with a series of large dark blotches with uneven white edges. These blotches are also wider than the spaces that separate them. Additionally, there is a lateral series of blotches that are usually darker than the dorsal blotches and clearly visible on all but the darkest specimens. The first rings of the tail are about the same color as the last body blotches, but these become progressively darker; the last two, at the base of the tail, are usually black. The belly is pale yellow, usually with brown spots. A large dark brown blotch on the snout has a pale border behind it that forms transverse bars on the supraoculars. There is a dark brown postocular stripe with a white border that extends from the eye to around the angle of the jaw. ^[2]

Common names

Western rattlesnake,^[2] northern Pacific rattlesnake,^[3] Pacific rattlesnake, black rattlesnake, Arizona diamond rattlesnake, black diamond rattlesnake, black snake, California rattlesnake, confluent rattlesnake, diamond-back rattlesnake, Great Basin rattlesnake, Hallowell's rattlesnake, Missouri rattlesnake, Oregon rattlesnake, Pacific rattler, rattlesnake, southern rattlesnake, western black rattlesnake, western rattler,^[4] north Pacific rattlesnake.^[5]

Geographic range

Found in North America from southwestern Canada, though much of the western half of the United States, and south into northern Mexico. In Canada it is found in southern British Columbia. In the USA it occurs in Washington, Oregon, western and southern Idaho, California, Nevada, Utah, Arizona, and likely west-central New Mexico. In northern Mexico it is found in western Baja California (state) and the extreme north of Baja California Sur, from sea level to an altitude of 2,500 m.^[2]

There are also reports of this species occurring on five different islands:^[2]

• Morro Rock, Morro Bay, San Luis Obispo County, California (now connected to the mainland by a causeway).
• Anaho Island, Pyramid Lake, Washoe County, Nevada.
• Rattlesnake Island, Clear Lake, Lake County, California (may no longer be found here).
• Santa Catalina Island, California, off the coast of San Pedro, Los Angeles, California.
• South Coronado Island, off the coast of Baja California.

The type locality is described as "... banks of the Oregon and Columbia River ... in the Oregon Territory."^[1]

Conservation status

This species is classified as Least Concern (LC) on the IUCN Red List of Threatened Species (v3.1, 2001).^[6] Species are listed as such due to their wide distribution, presumed large population, or because it is unlikely to be declining fast enough to qualify for listing in a more threatened category. The population trend is stable. Year assessed: 2007.^[7]

Subspecies

See also

• List of crotaline species and subspecies
• Crotalus by common name
• Crotalus by taxonomic synonyms
• Crotalinae by common name
• Crotalinae by taxonomic synonyms
• Snakebite

References