|Scientific Name:||Crotalus willardi Meek, 1905|
|Red List Category & Criteria:||Least Concern ver 3.1|
|Assessor(s):||Hammerson, G.A., Vazquez Díaz, J. & Quintero Díaz, G.E.|
|Reviewer(s):||Cox, N., Chanson, J.S. & Stuart, S.N. (Global Reptile Assessment Coordinating Team)|
Listed as Least Concern in view of its wide distribution, presumed large population, and because it is unlikely to be declining fast enough to qualify for listing in a more threatened category.
|Range Description:||The species' range extends from southeastern Arizona and extreme southwestern New Mexico south in the Sierra Madre Occidental through north-central and northeastern Sonora to western Chihuahua and (possibly disjunctly) to southern Durango and western Zacatecas, Mexico, at elevations of about 1,460 to 2,750 m (4,790 to 9,020 feet) (Campbell and Lamar 2004).
Subspecies obscurus occurs locally in the Animas Mountains (New Mexico), Peloncillo Mountains (Arizona and New Mexico), and Sierra de San Luis (Sonora and Chihuahua, Mexico) (Campbell et al. 1989, Holycross and Smith 1997, Campbell and Lamar 2004).
Subspecies willardi occurs in the Huachuca, Patagonia, Santa Rita, and Whetstone mountains of Arizona and southward into the Sierra de los Ojos, Sierra de Cananea, and Sierra Azul in north-central Sonora (Thirkhill and Starrett, 1992, Campbell and Lamar 2004).
Native:Mexico; United States
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||This species is represented by a fairly large number of occurrences (subpopulations). On a range-wide scale, Campbell and Lamar (2004) mapped about 43 collection sites. The adult population size is unknown but probably exceeds 10,000. This snake appears not to be abundant in most areas in the United States (Lowe et al. 1986), but it is regarded as fairly common in Mexico. In New Mexico, a population that appeared to be declining in the 1970s was well-protected and stable in the 1990s (Degenhardt et al. 1996). Currently, the extent of occurrence, area of occupancy, number of subpopulations, and population size are probably relatively stable or declining at a rate of less than 10% over 10 years or three generations.|
|Current Population Trend:||Stable|
|Habitat and Ecology:||The species' habitat includes montane areas of pine-oak, oak scrub, oak-juniper, and pine-fir woodland, foothill canyons in pinyon-juniper woodland, and relatively humid canyon bottoms with canopies of sycamore, alder, box elder, and maple, often along stream courses, in areas with rock outcrops or talus, or among downed logs (Lowe et al. 1986, Ernst 1992, Degenhardt et al. 1996, Ernst and Ernst 2003, Stebbins 2003, Campbell and Lamar 2004). At the southern end of the range, habitats include pine-covered plateaus with scattered open meadows, hillsides with scattered pines, oaks, madrones, and rocks, and brushy hilltops (Armstrong and Murphy 1979). This snake is basically terrestrial but may climb into low vegetation (Rossi and Feldner, 1993). It seeks cover in crevices, among or under rocks, wood, or other debris, in old stumps, or in similar sites.|
|Major Threat(s):||On a range-wide basis, no major threats are known. As of the early 1980s, populations in Arizona were not threatened (Johnson cited by Ernst 1992). Threats in Arizona include illegal collecting, mining, recreational development, and wood cutting (Lowe et al. 1986).|
|Conservation Actions:||Several occurrences of this species are in protected areas.|
|Citation:||Hammerson, G.A., Vazquez Díaz, J. & Quintero Díaz, G.E. 2007. Crotalus willardi. The IUCN Red List of Threatened Species 2007: e.T62253A12584209.Downloaded on 21 April 2018.|