Crotalus viridis - (Rafinesque, 1818)
Prairie Rattlesnake
Other English Common Names: prairie rattlesnake
Taxonomic Status: Accepted
Related ITIS Name(s): Crotalus viridis (Rafinesque, 1818) (TSN 174319)
French Common Names: crotale des prairies
Unique Identifier: ELEMENT_GLOBAL.2.768819
Element Code: ARADE02120
Informal Taxonomy: Animals, Vertebrates - Reptiles - Snakes
 
Kingdom Phylum Class Order Family Genus
Animalia Craniata Reptilia Squamata Viperidae Crotalus
Genus Size: D - Medium to large genus (21+ species)
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Concept Reference
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Concept Reference: Crother, B. I., J. Boundy, J. A. Campbell, K. de Quieroz, D. Frost, D. M. Green, R. Highton, J. B. Iverson, R. W. McDiarmid, P. A. Meylan, T. W. Reeder, M. E. Seidel, J. W. Sites, Jr., S. G. Tilley, and D. B. Wake. 2003. Scientific and standard English names of amphibians and reptiles of North America north of Mexico: update. Herpetological Review 34:198-203.
Concept Reference Code: A03CRO01NAUS
Name Used in Concept Reference: Crotalus viridis
Taxonomic Comments: Analysis of historical biogeography based on mtDNA data (Pook et al. 2000) revealed two main clades, one including populations from east and south of the Rocky Mountains and the other consisting of populations west of the Rocky Mountains. The conventionally recognized subspecies do not fully correspond to the phylogenetic pattern, and a review of the systematic status of several populations is needed (Pook et al. 2000).

Ashton and de Queiroz (2001) examined mtDNA variation among 26 populations of C. viridis and also identified two main clades: eastern, including subspecies viridis and nuntius (low levels of genetic divergence), and western, including all other subspecies. However, Ashton and de Queiroz (2001) differed from Pook et al. (2000) with respect to the relationships among members of the western clade, although Ashton and de Queiroz studied only a few individuals from each member of the western clade and stated that the relationships within the western clade are largely unresolved and that none (except possibly cerberus) appeared to deserve recognition as separate evolutionary species. Ashton and de Queiroz suggested that the two main clades be regarded as distinct species, C. viridis (eastern clade) and C. oreganus (western clade). The historical biogeographic scenario described by Ashton and de Queiroz (2001) suggests secondary contact between C. viridis and C. oreganus in northern Arizona, southwestern and northwestern Colorado, and southeastern Utah.

Douglas et al. (2002) examined mtDNA variation in C. viridis, with emphasis on the populations on the Colorado Plateau. As did Pook et al. (2000) and Ashton and de Queiroz (2001), they identified eastern and western clades, with the former including the nominal subspecies viridis and nuntius and the latter encompassing all of the other subspecies. Douglas et al. (2002) argued that all of the western subspecies should be recognized as species, but they did not effectively indicate details of distributional relationships in the contact zones among the proposed species. Douglas et al. (2002) concluded that the taxon nuntius should be regarded as a synonym of viridis.

Crother et al. (2003) considered all of the foregoing evidence and adopted the two-species taxonomy (Crotalus oreganus, Crotalus viridis) that is supported by the congruence among all three studies cited above. Campbell and Lamar (2004) also recognized only the two species. However, further clarification of the distributions of C. viridis and C. oreganus is needed, particularly in the contact zones in northern Arizona, southwestern and northwestern Colorado, and southeastern Utah. For example, populations in northwestern Colorado (Moffat County) identified by Douglas et al. (2002) as C. viridis were mapped as C. oreganus concolor by Campbell and Lamar (2004).

Venom characteristics indicate hybridization between C. viridis and C. scutulatus in New Mexico (Glenn and Straight 1990).
Conservation Status
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NatureServe Status

Global Status: G5
Global Status Last Reviewed: 29Aug2006
Global Status Last Changed: 11Dec2001
Rounded Global Status: G5 - Secure
Nation: United States
National Status: N5 (11Feb2005)
Nation: Canada
National Status: N3 (19May2015)

U.S. & Canada State/Province Status
United States Arizona (S1), Colorado (S5), Idaho (SNR), Iowa (S1), Kansas (S5), Montana (S4), Navajo Nation (S5), Nebraska (S4), New Mexico (S5), North Dakota (SNR), Oklahoma (S3), South Dakota (S5), Texas (S5), Utah (S5), Wyoming (S5)
Canada Alberta (S2S3), Saskatchewan (S3)

Other Statuses

Committee on the Status of Endangered Wildlife in Canada (COSEWIC): Special Concern (19May2015)
Comments on COSEWIC: Designated Special Concern in May 2015.
IUCN Red List Category: LC - Least concern

NatureServe Global Conservation Status Factors

Range Extent: 200,000 to >2,500,000 square km (about 80,000 to >1,000,000 square miles)
Range Extent Comments: 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 only the ranges of subspecies viridis and nuntius of traditionally defined C. viridis. In other words, the range extends from southern Alberta and southern Saskatchewan to the northern fringe of northern central Mexico, west to Idaho, Wyoming, Colorado, and extreme eastern Arizona, east to the Dakotas, western Iowa, Nebraska, central Kansas, central Oklahoma, and western and central Texas (Stebbins 2003, Campbell and Lamar 2004). 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, Herpetol. Rev. 35:190-191). Elevational range extends from about 100 meters near the Rio Grande (Campbell and Lamar 2004) to at least 2,895 meters (9,500 feet) in Colorado (Hammerson 1999).

Number of Occurrences: 81 to >300
Number of Occurrences Comments: This species is represented by a very large number of occurrences. On a range-wide scale, Campbell and Lamar (2004) mapped hundreds of collection sites (see also dot maps in Degenhardt et al. 1996 and Hammerson 1999).

Population Size: 100,000 to >1,000,000 individuals
Population Size Comments: Adult population size is unknown but certainly exceeds 100,000.

Number of Occurrences with Good Viability/Integrity: Many to very many (41 to >125)

Overall Threat Impact: Medium
Overall Threat Impact Comments: No major threats are known. Locally, populations have been eliminated or depleted as a result of killing at dens and loss/degradation of habitat by residential, commercial, and agricultural development (Hammerson 1999).

Short-term Trend: Relatively Stable (<=10% change)
Short-term Trend Comments: Currently, extent of occurrence, area of occupancy, and number of subpopulations, and population size probably are relatively stable or declining at a rate of less than 10 percent over 10 years or three generations.

Long-term Trend: Decline of <50% to Relatively Stable
Long-term Trend Comments: Some local populations have declined or disappeared as a result of historical killing of snakes at dens (Hammerson 1999, Ernst and Ernst 2003).

Other NatureServe Conservation Status Information

Distribution
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Global Range: (200,000 to >2,500,000 square km (about 80,000 to >1,000,000 square miles)) 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 only the ranges of subspecies viridis and nuntius of traditionally defined C. viridis. In other words, the range extends from southern Alberta and southern Saskatchewan to the northern fringe of northern central Mexico, west to Idaho, Wyoming, Colorado, and extreme eastern Arizona, east to the Dakotas, western Iowa, Nebraska, central Kansas, central Oklahoma, and western and central Texas (Stebbins 2003, Campbell and Lamar 2004). 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, Herpetol. Rev. 35:190-191). Elevational range extends from about 100 meters near the Rio Grande (Campbell and Lamar 2004) to at least 2,895 meters (9,500 feet) in Colorado (Hammerson 1999).

U.S. States and Canadian Provinces
Color legend for Distribution Map
Endemism: occurs (regularly, as a native taxon) in multiple nations

U.S. & Canada State/Province Distribution
United States AZ, CO, IA, ID, KS, MT, ND, NE, NM, NN, OK, SD, TX, UT, WY
Canada AB, SK

Range Map
Note: Range depicted for New World only. The scale of the maps may cause narrow coastal ranges or ranges on small islands not to appear. Not all vagrant or small disjunct occurrences are depicted. For migratory birds, some individuals occur outside of the passage migrant range depicted.

Range Map Compilers: NatureServe, 2005


U.S. Distribution by County Help
State County Name (FIPS Code)
AZ Apache (04001)
IA Plymouth (19149), Woodbury (19193)*
ID Ada (16001), Bannock (16005), Bingham (16011), Blaine (16013), Bonneville (16019), Butte (16023), Camas (16025), Canyon (16027)*, Caribou (16029)*, Custer (16037), Elmore (16039), Franklin (16041), Idaho (16049), Jefferson (16051)*, Jerome (16053)*, Kootenai (16055), Latah (16057), Lemhi (16059), Lewis (16061), Lincoln (16063), Nez Perce (16069), Oneida (16071)*, Owyhee (16073), Power (16077)*, Twin Falls (16083), Valley (16085), Washington (16087)*
UT San Juan (49037)
WA Adams (53001)+, Asotin (53003)+, Benton (53005)+, Chelan (53007)+, Columbia (53013)+, Douglas (53017)+, Ferry (53019)+, Franklin (53021)+, Garfield (53023)+*, Grant (53025)+, Kittitas (53037)+, Klickitat (53039)+, Lincoln (53043)+, Okanogan (53047)+, Skamania (53059)+, Spokane (53063)+*, Stevens (53065)+*, Walla Walla (53071)+, Whitman (53075)+*, Yakima (53077)+
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
10 Lower Big Sioux (10170203)+, Blackbird-Soldier (10230001)+*
14 Lower San Juan (14080205)+
15 Little Colorado headwaters (15020001)+, Upper Little Colorado (15020002)+*, Zuni (15020004)+
16 Middle Bear (16010202)+, Lower Bear-Malad (16010204)+*
17 Upper Spokane (17010305)+, Lower Spokane (17010307)*, Franklin D. Roosevelt Lake (17020001), Kettle (17020002)*, Colville (17020003)*, Sanpoil (17020004)*, Chief Joseph (17020005)*, Okanogan (17020006), Similkameen (17020007), Methow (17020008), Lake Chelan (17020009), Upper Columbia-Entiat (17020010), Wenatchee (17020011)*, Moses Coulee (17020012), Upper Crab (17020013)*, Banks Lake (17020014), Lower Crab (17020015), Upper Columbia-Priest Rapids (17020016), Upper Yakima (17030001), Naches (17030002), Lower Yakima, Washington (17030003)*, Idaho Falls (17040201)+*, Willow (17040205)+, Blackfoot (17040207)+, Portneuf (17040208)+, Lake Walcott (17040209)+, Upper Snake-Rock (17040212)+, Salmon Falls (17040213)+, Beaver-Camas (17040214)+*, Medicine Lodge (17040215)+, Little Lost (17040217)+, Big Lost (17040218)+, Big Wood (17040219)+, Camas (17040220)+, Little Wood (17040221)+, C. J. Idaho (17050101)+, Bruneau (17050102)+*, Middle Snake-Succor (17050103)+, Upper Owyhee (17050104)+, South Fork Owyhee (17050105)+, East Little Owyhee. Nevada, (17050106)+, Jordan (17050108)+, North and Middle Forks Boise (17050111)+, South Fork Boise (17050113)+*, Lower Boise (17050114)+*, Weiser (17050124)+*, Brownlee Reservoir (17050201)+*, Lower Snake-Asotin (17060103)+, Lower Grande Ronde (17060106)*, Lower Snake-Tucannon (17060107)*, Palouse (17060108)+*, Rock (17060109)*, Lower Snake (17060110), Upper Salmon (17060201)+, Pahsimeroi (17060202)+, Middle Salmon-Panther (17060203)+, Lemhi (17060204)+, Lower Middle Fork Salmon (17060206)+, South Fork Salmon (17060208)+, Lower Salmon (17060209)+, Clearwater (17060306)+, Middle Columbia-Lake Wallula (17070101), Walla Walla (17070102)*, Middle Columbia-Hood (17070105)*, Klickitat (17070106)
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
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Basic Description: A venomous snake.
Reproduction Comments: Mating occurs mostly from mid-summer to early fall, mainly in late summer in central U.S. (Aldridge, 1993, J. Herpetol. 27:481-484), occasionally in spring. Young are born usually in August-October. Litter size increases with female size (average 5 where body size is small, maximum about 25 in the largest females where body size is large. Individual adult females may not give birth in some years, probably depending on nutritional status; interval between litters was 2 or more years in Wyoming (Graves and Duvall 1992). Requires several years to reach sexual maturity in areas with short growing season. Pregnant females may congregate in 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.

Non-Migrant: Y
Locally Migrant: Y
Long Distance Migrant: N
Mobility and Migration Comments: In some populations, individuals may migrate up to several km (up to 11 km or more in Wyoming) between winter den and summer range (Duvall et al. 1985, 1990).

Exhibits fidelity to winter den site.

Palustrine Habitat(s): Riparian
Terrestrial Habitat(s): Bare rock/talus/scree, Cliff, Cropland/hedgerow, Desert, Forest Edge, Forest/Woodland, Grassland/herbaceous, Savanna, Shrubland/chaparral, Woodland - Conifer, Woodland - Hardwood, Woodland - Mixed
Special Habitat Factors: Burrowing in or using soil, Fallen log/debris
Habitat Comments: This snake inhabits a wide diversity of habitats, from prairies and arid basins to wooded mountains (Lowe et al. 1986, Degenhardt et al. 1996, Hammerson 1999, Werler and Dixon 2000, Stebbins 2003, Campbell and Lamar 2004, Werner et al. 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 (Gannon and Secoy 1985, Graves and Duvall 1992).
Adult Food Habits: Carnivore
Immature Food Habits: Carnivore
Food Comments: Diet includes mainly small mammals; also birds, lizards, and rarely amphibians (see Ernst 1992). Juveniles in some regions prey mostly on lizards rather than on small mammals.
Adult Phenology: Crepuscular, Diurnal, Hibernates/aestivates, Nocturnal
Immature Phenology: Crepuscular, Diurnal, Hibernates/aestivates, Nocturnal
Phenology Comments: Mostly diurnal in cool weather, active in evening and at night in hot summer weather (morning and late afternoon in far north, Gannon and Secoy 1985). Active primarily from about late March or April to October or November over most of range.
Length: 163 centimeters
Economic Attributes
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Economic Comments: Venomous.
Management Summary Not yet assessed
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Population/Occurrence Delineation
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Use Class: Not applicable
Subtype(s): Hibernaculum
Minimum Criteria for an Occurrence: Occurrences are based on evidence of historical presence, or current and likely recurring presence, at a given location. Such evidence minimally includes collection or reliable observation and documentation of one or more individuals in or near appropriate habitat where the species is presumed to be established and breeding.
Separation Barriers: Busy highway or highway with obstructions such that snakes rarely if ever cross successfully; major river with consistently fast flow; densely urbanized area dominated by buildings and pavement.
Separation Distance for Unsuitable Habitat: 1 km
Separation Distance for Suitable Habitat: 5 km
Alternate Separation Procedure: A longer separation distance for suitable habitat can be used if site-specific data indicate that it is warranted.
Separation Justification: These snakes can cross rivers, so only the largest and fastest rivers should be regarded as barriers.

Although individuals in a Wyoming population may move up to 11 km or more between the hibernaculum and summer range (Duvall et al. 1985, 1990, 1992), studies of movements of the closely related species C. oreganus in Arizona, California, and Utah indicate that maximum activity range lengths (and/or maximum distance of summer locations from hibernacula) are more typically 1.5 km or less, and range lengths of this magnitude probably are more characteristic of most populations of C. viridis than are the extremes documented in Wyoming. The separation distance of 5 km for suitable habitat is about three times a typical activity range length for C. oreganus.

Inferred Minimum Extent of Habitat Use (when actual extent is unknown): 1.5 km
Inferred Minimum Extent Justification: Based on movements of this species and other snakes of this size, suitable habitat within 1.5 km of a point location (especially a hibernaculum), is likely to be occupied.
Date: 18Jul2005
Author: Hammerson, G.
Population/Occurrence Viability
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U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
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Authors/Contributors
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NatureServe Conservation Status Factors Edition Date: 29Aug2006
NatureServe Conservation Status Factors Author: Hammerson, G.
Element Ecology & Life History Edition Date: 14May2013
Element Ecology & Life History Author(s): Hammerson, G.

Zoological data developed by NatureServe and its network of natural heritage programs (see Local Programs) and other contributors and cooperators (see Sources).

References
Help
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Patterson, B.D., G. Ceballos, W. Sechrest, M.F. Tognelli, T. Brooks, L. Luna, P. Ortega, I. Salazar, and B.E. Young. 2003. Digital Distribution Maps of the Mammals of the Western Hemisphere, version 1.0. NatureServe, Arlington, Virginia, USA.

Acknowledgement Statement for Mammal Range Maps of North America:
"Data provided by NatureServe in collaboration with Bruce Patterson, Wes Sechrest, Marcelo Tognelli, Gerardo Ceballos, The Nature Conservancy-Migratory Bird Program, Conservation International-CABS, World Wildlife Fund-US, and Environment Canada-WILDSPACE."

Citation for Amphibian Range Maps of the Western Hemisphere:
IUCN, Conservation International, and NatureServe. 2004. Global Amphibian Assessment. IUCN, Conservation International, and NatureServe, Washington, DC and Arlington, Virginia, USA.

Acknowledgement Statement for Amphibian Range Maps of the Western Hemisphere:
"Data developed as part of the Global Amphibian Assessment and provided by IUCN-World Conservation Union, Conservation International and NatureServe."

NOTE: Full metadata for the Bird Range Maps of North America is available at:
http://www.natureserve.org/library/birdDistributionmapsmetadatav1.pdf.

Full metadata for the Mammal Range Maps of North America is available at:
http://www.natureserve.org/library/mammalsDistributionmetadatav1.pdf.

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