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Overview

Brief Summary

Common Names

Ridge-nosed rattlesnake

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Notes

Holotype: FMNH 902

Type-locality: "Tombstone, Arizona." (McDiarmid et al., 1999).

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A small rattlesnake with a coloration that matches the fallen leaf litter in its habitat. Placement of white face stripes (or lack thereof in the obscurus subspecies) distinguish the subspecies.

Found in the mid to high elevation oak-pine woodlands of southeastern Arizona, southwestern New Mexico, Sonora, Chihuahua, Durango and Zacatecas. Yet to be found in the woodlands of Sinaloa, Nayarit and Jalisco.

In the summer of 1900, ornithologist Francis Cottle Willard collected the type specimen of Crotalus willardi in the environs of Ramsey Canyon near the Hamburg mine and settlement in the Huachuca Mountains of southeastern Arizona. This was amended from Toombstone, Arizona by ornithologist Henry Swarth in 1921.

The snake was in a collection of Willard's specimens, which also included the type of the Southern Pacific Rattlesnake. This collection was acquired by Edmund C. Heller and ichthyologist Seth Eugene Meek reported on and described two new species in the collection: the Southern Pacific Rattlesnake (Crotalus [oreganus] helleri) in honor of Heller and the Ridge-nosed Rattlesnake (Crotalus willardi) in honor of Willard. The paper was published in 1905 but not printed until 1906. Ergo the citation for both species is "Meek 1905(1906)".

In 1897 the first specimen of C. willardi was collected for science on the Smithsonian Institution/United States National Museum of Natural History's Nelson-Goldman Mexican biological expedition (of several years). This was in the southern end of the Sierra Madre Occidental mountain chain on the Durango-Zacatecas state line and remains the southernmost specimen of the species.

In 1949, Laurence M. Klauber, the late preeminent authority on rattlesnakes, would describe this and other later southern specimens as the meridionalis subspecies (C. w. meridionalis: Southern Ridge-nosed Rattlesnake) in reference to the southern latitude of the subspecies as the southern extent of the species range.

In the same paper, apart from describing the nominate subspecies (C. w. willardi: Arizona Ridge-nosed Rattlesnake), Klauber would describe the silus subspecies (C. w. silus: Chihuahuan Ridge-nosed Rattlesnake) in reference to its snub nose for specimens from the northern Sierra Madre Occidental of Sonora and Chihuahua and some of its outlying mountain ranges in Sonora.

In 1959 James D. Anderson collected a specimen of the species from the Sierra del Nido mountain range in northwestern Chihuahua. He later described this isolated population as the amabilis subspecies (C. w. amabilis: Del Nido Ridge-nosed Rattlesnake) in reference to its beauty in 1962.

The last and most debated subspecies to be described was C. w. obscurus (New Mexico Ridge-nosed Rattlesnake), in reference to the lack of facial stripes characteristic of the species. In 1974, Herbert S. Harris Jr. perhaps unknowingly and unintentionally described C. w. obscurus in a popular non-peer-reviewed magazine describing its vulnerable status in the US by meeting the minimum international requirements of a species description.

He was later heavily criticized for this article after describing the subspecies with Robert S. Simmons in a more traditional species description in an article summarizing the paleogeography and morphology of C. willardi in 1976.

Apart from the 1974 article, the description also lacked apparent peer review (despite acknowledging reviewers) and was published in a the Bulletin of the Maryland Herpetological Society of which Harris was the chief editor (conflict of interest).

Despite unorthodoxy, C. w. obscurus was described in two publications owing to the fact that the second one designated paratypes, specific type locality and other key information lacking or unelaborated in the first. Authors continue to cite between Harris (1974) and Harris and Simmons (1976).

Many rattlesnake biologists didn't accept this taxon and considered it a variant population of C. w. silus (possibly knowing the unique status of the taxon but resisting the questionable methods of the taxon author(s)) until David L. Barker supported the status of all five subspecies using molecular data in 1992.

Recent range records include a specimen from the Sierra Pinitos in north central Sonora and a specimen from the Sierra Madera near Magdalena, Sonora. The former being the westernmost population in Mexico. Other ranges await documentation of the species in the US and Mexico.

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The Ridge-nosed Rattlesnake, Crotalus willardi Meek 1905(1906) , is a Madrean species meaning that it is endemic to the high elevation ecoregions shared by the Sierra Madre mountain chains and their outlying ranges (sky islands) in Mexico. There are at least six significant mountain ranges that can fall under or be considered “Sierra Madre” according to West (1964) in Armstrong and Murphy (1979), Tamayo (1949) in Leopold (1972), and Flores-Villela (1993a). C. willardi is known only from the Sierra Madre Occidental and her outlying ranges.
More specifically, authors have subcategorized C. willardi and its subspecies as endemic to the woodland ecoregion and its subregions within the Sierra Madre Occidental under various names depending on one’s reference. For this work the term Madrean Evergreen Woodland of Brown (1994) is used unless otherwise noted.
The species is thought to have lived in more tropical conditions at lower elevations ca. 15-39 million years ago during the early formation of the Sierra Madre Occidental and her outlying ranges, and persisted by adapting with the formation of the present Madrean Evergreen Woodland and the communities associated with it (Van Devender 1992). Authors attribute its current subspeciation to coincide with the geologic and climactic fluctuations that formed the specific woodlands of the Sierra Madre Occidental during the mid to late Pliocene and later pluvial periods of the Pleistocene (Axelrod 1950, 1958, Marshall 1957) when tropical biomes receded south and the oak-pine woodlands receded up in elevation being isolated by grassland and desert or thornforest (Van Devender 1992, Marshall 1957). These woodlands are part of the Northern Young Element of Savage (1960, 1966) that developed from tropical origin and closely associated with the Madro-Tertiary Geoflora, and the Arizona component of the Sierra Madrean woodland element of the Madro-Tertiary Geoflora of Axelrod (1950) (Harris and Simmons 1976, Felger and Wilson 1995).

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Distribution

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

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Global Range: (200,000-2,500,000 square km (about 80,000-1,000,000 square miles)) The 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 1,460-2,750 meters (4,790-9,020 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, Herpetol. Rev. 23:124; Campbell and Lamar 2004).

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Continent: Middle-America North-America
Distribution: USA (SE Arizona: Santa Rita Mountains, Patagonia Mountains, Canelo Hills-Huachuca Mountains, Whetstone Mountains; SW New Mexico),  Mexico (Sonora, Chihuahua, Durango: Sierra Madre Occidental and associated highlands)  willardi: S Arizona, N Sonora;
Type locality: Tombstone, Arizona.  amabilis: Sierra del Nido, Mexico  meridionalis: S Durango, NW Zacatecas  obscurus: NE Sonora, NW Chihuahua, S Arizona (Peloncillo Mountains; Bryan Starrett, pers. comm.).  silus: NE Sonora, W Chihuahua, SW New Mexico (USA)
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Mountains of southwestern United States (southeastern Arizona and southwestern New Mexico) and northwestern Mexico (highlands of the Sierra Madre Occidental in the states of Sonora, Chihuahua, Durango, and Zacatecas) (McDiarmid et al., 1999).

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Physical Description

Size

Length: 61 cm

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Ecology

Habitat

Habitat and Ecology

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.

Systems
  • Terrestrial
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Comments: 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 buy may climb into low vegetation (Rossi and Feldner, 1993, Herpetol. Rev. 24:35). It seeks cover in crevices, among or under rocks, wood, or other debris, in old stumps, or in similar sites.

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Migration

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.

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Trophic Strategy

Comments: Preys on scorpions, centipedes, lizards, small mammals and birds.

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Population Biology

Number of Occurrences

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

Estimated Number of Occurrences: 21 - 300

Comments: 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.

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Global Abundance

10,000 - 100,000 individuals

Comments: Adult population size is unknown but likely 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.

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General Ecology

Distance per move in New Mexico averaged less than 27 m, and daily activity areas averaged less than 225 sq m, but annual home range size was not reported (Smith et al. 2001).

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Activity is based around seasonal summer rain when prey and mates are active, although basking is not unheard of during warm periods in winter.

Females birth in late summer to fall and remain with the litter until its first shed of skin. According to a long-term observer of the species in the Huachuca mountains, there is an apparent order to which the young emerge to and from basking.

Despite the occurrence of bright tail coloration in the young of C. willardi, there are no records of them using their tails to mimic the prey (caterpilars/grubs) of their prey (lizards and arthropods such as centipedes) when young.

As the young mature, there is an ontogenic shift in diet from arthropods and young lizards to adult lizards, birds and small mammals.

The species faces a multitude of threats; however mainly habitat destruction via grazing and un-natural and human-altered fire regimes. Specifically the obscurus subspecies is federally protected in the US due to it's limited range in a fire and grazing -threatened and -altered habitat.

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Life History and Behavior

Cyclicity

Comments: Inactive in cold temperatures and extreme heat. Mainly diurnal but probably at least partially nocturnal during hot summer weather; in summer, most active on warm humid mornings; rains may stimulate late afternoon activity; in fall, active mainly in afternoon (Ernst 1992). Most active before or after showers when air temperatures are 24-29 C (Armstrong and Murphy 1979). In Arizona, active from April or early May through mid-November (Lowe et al. 1986, Ernst 1992). In New Mexico, most active during daylight hours from July through September.

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Life Expectancy

Lifespan, longevity, and ageing

Maximum longevity: 21.3 years (captivity)
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Reproduction

Northern part of range: copulates in midsummer to early fall; ovulation and fertilization occur probably in early spring; bears 2-9 young, late July through August; adult females typically produce young at intervals of two years or more (Holycross and Goldberg 2001).

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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage: Crotalus willardi

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 3
Species With Barcodes: 1
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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
LC
Least Concern

Red List Criteria

Version
3.1

Year Assessed
2007

Assessor/s
Hammerson, G.A., Vazquez Daz, J. & Quintero Daz, G.E.

Reviewer/s
Cox, N., Chanson, J.S. & Stuart, S.N. (Global Reptile Assessment Coordinating Team)

Contributor/s

Justification
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.
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National NatureServe Conservation Status

United States

Rounded National Status Rank: N2 - Imperiled

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NatureServe Conservation Status

Rounded Global Status Rank: G5 - Secure

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Population

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.

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

Comments: Currently, extent of occurrence, area of occupancy, 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.

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

Comments: 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).

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Threats

Major Threats
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).
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Degree of Threat: Medium

Comments: 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).

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Management

Conservation Actions

Conservation Actions
Several occurrences of this species are in protected areas.
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Management Requirements: Reintroduction of fire may be important in maintaining habitat, but reduction of artificially high fuel loads may be needed to prevent habitat damage and mortality from fire (Smith et al. 2001).

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Relevance to Humans and Ecosystems

Benefits

Economic Uses

Comments: Venomous; mild mannered but will turn and bite if grasped; venom is of relatively low toxicity and snake can inject only a relatively small volume, so not especially dangerous to humans (Ernst 1992).

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Wikipedia

Crotalus willardi

Common names: ridge-nosed rattlesnake, Willard's rattlesnake, Willard's rattler[2]

Crotalus willardi is a venomous pit viper species found in the southwestern United States and Mexico. It is the most recent rattlesnake species to be discovered in the United States. Its specific name is in honor of its discoverer, Professor Frank C. Willard.[3] Five subspecies are currently recognized, including the nominate subspecies described here.[4] The Arizona ridge-nosed rattlesnake is the state reptile of Arizona.

Description[edit]

C. willardi is a rather small rattlesnake with all subspecies measuring one to two feet (30-60 cm) in length. Color patterns are generally a dark brown base with pale or white horizontal striping, but vary slightly between subspecies. The distinctive ridges along each side of its nose, which are a series of upturned scales, are unique to its species and are the origin of its name.

Habitat[edit]

C. willardi is rarely found outside habitats at high elevation. Wooded mountain ranges, primarily in the southwest, are where this reclusive species is found. Each subspecies’ range is limited to select mountain ranges, making human encounters rare events.

Conservation status[edit]

This species is classified as Least Concern on the IUCN Red List of Threatened Species (v3.1, 2001).[5] 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.[6]

Although four of the five subspecies are secure, the New Mexico ridge-nosed rattlesnake (C. w. obscurus) is an endangered species and listed as threatened by the US Fish and Wildlife Service. Remaining populations are scattered throughout New Mexico, Arizona and the northern part of Mexico. Habitat destruction is the cause of declining numbers, but critical habitat designations (recovery measures) have been proposed.

Behavior[edit]

Rattlesnakes are primarily ambush hunters; they coil and lie waiting for prey to approach within striking distance. The diet of C. willardi includes small mammals, lizards, birds, and large centipedes. The young feed primarily on large centipedes (Scolopendra spp.) and lizards, whereas adults feed primarily on mammals and birds. [7]

Like other rattlesnakes, C. willardi is ovoviviparous, meaning it gives birth and does not lay eggs. Contrasting with viviparous animals, the young still develop within an egg inside the female snake until their time of birth. Copulation occurs from late summer to early fall, and gestation lasts about four to five months. Females give birth to two to 9 (average five) young in late July or August. Both sexes appear to reach reproductive maturity around 400 mm (16 in) in body (snout to vent) length. Although captive snakes have reproduced annually, wild females probably reproduce every second or third year.[8]

Venom[edit]

Due to the generally small size of the snake, venom discharge yields are low; thus, the largely hemotoxic venom is not as life-threatening as that of other rattlesnakes. No documented deaths have been caused by ridge-nosed rattlesnakes, but pain and discomfort can still result from a rare bite.

Subspecies[edit]

Subspecies[4]Taxon author[4]Common name[9]Geographic range[10][11]
C. w. amabilisAnderson, 1962Del Nido ridge-nosed rattlesnakeMexico in north-central Chihuahua
C. w. meridionalisKlauber, 1949Southern ridge-nosed rattlesnakeMexico in southern Durango and southwestern Zacatecas
C. w. obscurusHarris & Simmons, 1974New Mexico ridge-nosed rattlesnakeThe US in extreme southeastern Arizona and extreme southwestern New Mexico, Mexico in extreme northwestern Chihuahua and extreme northeastern Sonora
C. w. silusKlauber, 1949Chihuahuan ridge-nosed rattlesnakeWestern Chihuahua and eastern Sonora
C. w. willardiMeek, 1905Arizona ridge-nosed rattlesnakeSoutheastern Arizona, and northern Sonora

See also[edit]

References[edit]

  1. ^ 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).
  2. ^ Wright AH, Wright AA. 1957. Handbook of Snakes. Comstock Publishing Associates. (7th printing, 1985). 1105 pp. ISBN 0-8014-0463-0.
  3. ^ Biographies of People Honored in the Names of the Reptiles and Amphibians of North America
  4. ^ a b c "Crotalus willardi". Integrated Taxonomic Information System. Retrieved 16 May 2007. 
  5. ^ Crotalus willardi at the IUCN Red List. Accessed 13 September 2007.
  6. ^ 2001 Categories & Criteria (version 3.1) at the IUCN Red List. Accessed 13 September 2007.
  7. ^ Holycross et al. 2002
  8. ^ Holycross and Goldberg 2001
  9. ^ Mehrtens JM. 1987. Living Snakes of the World in Color. New York: Sterling Publishers. 480 pp. ISBN 0-8069-6460-X.
  10. ^ Campbell JA, Lamar WW. 2004. The Venomous Reptiles of the Western Hemisphere. 2 volumes. Comstock Publishing Associates, Ithaca and London. 870 pp. 1500 plates. ISBN 0-8014-4141-2.
  11. ^ Klauber LM. 1997. Rattlesnakes: Their Habitats, Life Histories, and Influence on Mankind. Second Edition. 2 volumes. Reprint, University of California Press, Berkeley. ISBN 0-520-21056-5.

Further reading[edit]

  • Holycross, A.T., C.W. Painter, D.G. Barker and M.E. Douglas. 2002. Foraging ecology of the threatened New Mexico Ridge-nosed Rattlesnake (Crotalus willardi obscurus). In Schuett, G.W., M. Höggren, M.E. Douglas and H.W. Greene (eds.), Biology of the Vipers, pp. 243-251. Eagle Mountain Publishing, Eagle Mountain, Utah. 596 pp.
  • Holycross, A.T. and S.R. Goldberg. 2001. Reproduction in northern populations of the ridgenose rattlesnake, Crotalus willardi (Serpentes: Viperidae). Copeia 2001:473-481.
  • Meek, S.E. 1905. An annotated list of a collection of reptiles from southern California and northern Lower California. Field Columbian Museum Zoölogical Series 7(1):1-19, Plates I.-III.
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Names and Taxonomy

Taxonomy

Comments: See Campbell et al. (1989) for record of apparent hybridization with C. lepidus in southwestern New Mexico.

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