Crotalus oreganus

Grand canyon rattlesnake

Arizona black rattlesnake

Midget faded rattlesnake

Southern Pacific rattlesnake

Great basin rattlesnake

Northern Pacific rattlesnake

As defined by Crother et al. (2003), following congruence of Pook et al. (2000), Ashton and de Queiroz (2001), and Douglas et al. (2002), this species encompasses the ranges of all subspecies of traditionally defined C. viridis except viridis and nuntius (i.e., southern British Columbia in western Canada, through the western United States (east to the Rocky Mountains) to central Baja California in Mexico). The ranges and relationships of Crotalus oreganus and Crotalus viridis in the Four Corners region and in northwestern Colorado need further clarification (Hammerson 1999, Brennan and Holycross 2004). The species avoids arid areas such as the Mojave and Colorado Deserts. The elevational range extends from sea level to around 3,355 m asl (11,000 feet) but most localities are below 2,745 m asl (9,000 feet) (Basey 1976, Stebbins 2003, Campbell and Lamar 2004).

occurs (regularly, as a native taxon) in multiple nations

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: (200,000-2,500,000 square km (about 80,000-1,000,000 square miles)) 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).

Continent: Middle-America North-America
Distribution: SW Canada, W USA (Washington, California, Oregon ?, Montana),   caliginis: South Coronado Island, off the coast of Baja California  concolor: basins of the Colorado and Green Rivers  helleri: SW California, south into Baja California  lutosus: Great Basin between the Rocky Mountains and the Sierra Nevada.  oreganus: Pacific slopes est of the Cascades and west of the Sierra Nevada, from British Columbia to NE California.

Southwestern Canada and western USA.

Habitat and Ecology

Systems

• Terrestrial

Comments: This snake occupies a wide diversity of habitats, from shrubby coastal dunes to timberline, from shrubby basins and canyons to open mountain forests (Nussbaum et al. 1983, Lowe et al. 1986, Brown et al. 1995, Hammerson 1999, Stebbins 2003, Campbell and Lamar 2004). It is primarily terrestrial but sometimes climbs into trees or shrubs. When inactive, it occupies mammal burrows, crevices, caves, or similar secluded sites. Pregnant females may congregate near the winter den until parturition (Ashton and Patton 2001).

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Summer activity range evidently varies geographically; the largest size reported by Macartney et al. (1988) and Ernst (1992) was from California, where the average was 12 ha in males and 6.5 ha in females. Similarly, along the Little Colorado River in Arizona, five radio-tracked individuals for which at least 50 locations were obtained had activity ranges of 4-34 ha (mean = 11.6 ha) minimum convex polygon) (Reed and Douglas 2002). Activity ranges were elongate, corresponding to the canyon bottom, and included both summer and winter habitats.

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).

Comments: Eats 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.

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: > 300

Comments: This species is represented by a large number (hundreds) of occurrences (subpopulations) (Campbell and Lamar 2004).

100,000 to >1,000,000 individuals

Comments: Adult population size is unknown but presumably exceeds 100,000. This snake is fairly common in many areas.

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.

Comments: These snakes are active mostly in daytime in cool weather but mainly in the evening and at night in hot summer weather (morning and late afternoon in far north). They are active from about April to November over most of the range but in warm climates such as in southern California some may be above ground in any month. At the northern end of the range in southern British Columbia and Idaho most activity occurs from late March or April to early October (Macartney 1989, Wallace and Diller 2001). In southern California, some may be above ground in any month.

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.

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 2
Species With Barcodes: 1

Year Assessed

Assessor/s

Reviewer/s

Justification

Canada

Rounded National Status Rank: N3 - Vulnerable

United States

Rounded National Status Rank: N5 - Secure

Rounded Global Status Rank: G5 - Secure

Population

Population Trend

Global Short Term Trend: Relatively stable (=10% change)

Comments: Currently, extent of occurrence, area of occupancy, and number of subpopulations probably are relatively stable; population size may be declining but likely at a rate of less than 10 percent over 10 years or three generations.

Global Long Term Trend: Increase of 10-25% to decline of 30%

Comments: Extent of occurrence, area of occupancy, and number of subpopulations probably are relatively stable; population size has declined in many areas in comparison to historical levels (e.g., see Ernst and Ernst 2003).

Degree of Threat: Medium

Comments: No major threats are known. Locally, populations are being reduced as a result of persecution and habitat loss and degradation from residential, commercial, and agricultural development.

Major Threats

Conservation Actions

Global Protection: Very many (>40) occurrences appropriately protected and managed

Comments: Many occurrences are in protected areas.

Comments: Venomous; human deaths in untreated cases have occurred 18 hours to 5 days after the bite (Ernst 1992); venom of subspecies concolor of eastern Utah and western Colorado is 10-30 times more toxic than that of any other subspecies (Glenn and Straight).