Crotalus oreganus is a venomous pit viper species found in North America in the western United States, parts of British Columbia, and northwestern Mexico. Seven subspecies are currently recognized, including the nominate subspecies described here.
The size of this species varies greatly, with some populations being stunted and others growing very large. Mainland specimens often reach 100 cm (39 in) in length, with the largest on record being 162.6 cm (64.0 in) (Klauber, 1956) for C. o. oreganus.
This species, in its various forms, shows considerable ontogenetic variation. Juveniles usually have more or less distinct patterns, but these fade as the animals mature. The color of the iris often matches the ground color, which may be bronze, gold, or different shades of tan, pink, or gray.
The color pattern of the typical form, C. o. oreganus, has a dark-brown, dark-gray, olive-brown, or sometimes black or pale yellowish ground color 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, a lateral series of blotches, usually darker than the dorsal blotches, is 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 rings become progressively darker; the last two rings, 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.
Its common names include western rattlesnake, northern Pacific rattlesnake, 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, and north Pacific rattlesnake.
It is found in North America from southwestern Canada, through 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 US, 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 and the extreme north of Baja California Sur, from sea level to an altitude of 2,500 metres (8,200 ft).
This species also reportedly occurs on six different islands:
- 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
- South Coronado Island, one of the Coronado Islands off the coast of Baja California.
- Mare Island, Vallejo, California (now connected by a land bridge)
Using its heat-sensing facial pits to locate prey, C. oreganus eats birds, bird eggs, and small mammals, from mice up to and including rabbits. It also eats small reptiles and amphibians. The juveniles eat insects.
Sexually mature females bear live young in broods of as many as 25.
This species is classified as Least Concern on the IUCN Red List of Threatened Species (v3.1, 2001). Species are listed as such due to their wide distribution, presumed large population, or because they are unlikely to be declining fast enough to qualify for listing in a more threatened category. The population trend was stable when assessed in 2007.
|Subspecies||Taxon author||Common name||Geographic range|
|C. o. abyssus||Klauber, 1930||Grand Canyon rattlesnake||The US in Arizona in the Grand Canyon of the Colorado River, from the north to the south rim|
|C. o. caliginis||Klauber, 1949||Coronado Island rattlesnake||Mexico, on South Coronado Island, off the northwest coast of Baja California|
|C. o. cerberus||(Coues In Wheeler, 1875)||Arizona black rattlesnake||Arizona from the Hualpi Mountains and Cottonwood Cliffs in the northwest, southeast to the Santa Catalina, Rincon, Pinaleno and Blue Mountains, Steeple Rock in extreme western New Mexico|-|
|C. o. concolor||Woodbury, 1929||Midget faded rattlesnake||Colorado and Green River basins of southwestern Wyoming, Utah east of 111°W (excluding the southeastern corner) and extreme east-central Colorado|
|C. o. helleri||Meek, 1905||Southern Pacific rattlesnake||Southern California, west of the desert, in the north from the counties of San Luis Obispo and Kern, and south through the counties of Santa Barbara, Ventura, Los Angeles (including Santa Catalina Island), southwestern San Bernardino, Orange, western Riverside, San Diego and extreme western Imperial, south though Baja California to 28° 30'N|
|C. o. lutosus||Klauber, 1930||Great Basin rattlesnake||Great Basin region, Idaho south of 44°N, Utah west of 111°W, Arizona west and north of the Colorado River, as well as the north rim of the Grand Canyon, Nevada (excluding Esmeralda, Nye and Clark Counties), California east of the Sierra Nevada from Lower Klamath Lake south to below Lake Mono, Oregon south and east of the line Upper Klamath Lake-Fort Rock-Burns-Council (Idaho)|
|C. o. oreganus||Holbrook, 1840||Northern Pacific rattlesnake||From the Pacific slope in British Columbia, Canada, south through the United States to San Luis Obispo County and Kern County in California, south-central British Columbia, Washington east of the Cascade Mountains, western Idaho from Coeur d'Alene south to near Council or Weiser, northern and western Oregon (excluding the Cascades), and California west of the Sierra Nevada, on Morro Rock off the coast of San Luis Obispo County|
- List of crotaline species and subspecies
- Crotalus by common name
- Crotalus by taxonomic synonyms
- Crotalinae by common name
- Crotalinae by taxonomic synonyms
- McDiarmid RW, Campbell JA, Touré T. 1999. Snake Species of the World: A Taxonomic and Geographic Reference, vol. 1. Herpetologists' League. 511 pp. ISBN 1-893777-00-6 (series). ISBN 1-893777-01-4 (volume).
- Ashton KG, de Queiroz A. 2001. Molecular systematics of the western rattlesnake, Crotalus viridis (Viperidae), with comments on the utility of the d-loop in phylogenetic studies of snakes. Molecular Phylogenetics and Evolution, Vol. 21, No.2, pp. 176-189. PDF at CNAH. Accessed 3 September 2008.
- Campbell JA, Lamar WW. 2004. The Venomous Reptiles of the Western Hemisphere. Comstock Publishing Associates, Ithaca and London. 870 pp. 1500 plates. ISBN 0-8014-4141-2.
- "Crotalus oreganus". Integrated Taxonomic Information System. Retrieved 28 November 2006.
- Wright AH, Wright AA. 1957. Handbook of Snakes. Comstock Publishing Associates. (7th printing, 1985). 1105 pp. ISBN 0-8014-0463-0.
- Klauber LM. 1997. Rattlesnakes: Their Habitats, Life Histories, and Influence on Mankind. Second Edition. First published in 1956, 1972. University of California Press, Berkeley. ISBN 0-520-21056-5.
- Parker HW, Grandison AGC. 1977. Snakes -- a natural history. Second Edition. British Museum (Natural History) and Cornell University Press. 108 pp. 16 plates. LCCCN 76-54625. ISBN 0-8014-1095-9 (cloth), ISBN 0-8014-9164-9 (paper).
- Hubbs, Brian and Brendan O'Connor. 2012. A Guide to the Rattlesnakes and other Venomous Serpents of the United States. Tricolor Books. Tempe, Arizona. 129 pp. ISBN 978-0-9754641-3-7. (Crotalus o. oreganus, pp. 22-23.)
- Crotalus oreganus at the IUCN Red List. Accessed 13 September 2007.
- 2001 Categories & Criteria (version 3.1) at the IUCN Red List. Accessed 13 September 2007.
- Holbrook, J.E. 1840. North American Herpetology; or, A Description of the Reptiles Inhabiting the United States. Vol. IV. [First Edition.] Dobson. Philadelphia. 126 pp. (Crotalus oreganus, pp. 115–117.)
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