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Ridge-nosed Rattlesnake (Crotalus willardi)

[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column][/vc_row][vc_row][vc_column width=”1/2″][vc_single_image image=”2152″ img_size=”large” alignment=”center” style=”vc_box_rounded”][vc_column_text]Ridge-nosed Rattlesnake (C.w. obscurus). Photo by Young Cage[/vc_column_text][/vc_column][vc_column width=”1/2″][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”2698″ img_size=”medium” alignment=”center” onclick=”img_link_large”][vc_column_text]Ridge-nosed Rattlesnake (C.w. willardi). Photo by Jim Rorabaugh[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][vc_column_inner width=”1/2″][vc_single_image image=”2699″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Ridge-nosed Rattlesnake (C.w. obscurus), Sierra San Luis, Sonora, MX. Photo by Jim Rorabaugh[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][/vc_row_inner][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”2700″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Ridge-nosed Rattlesnake (C.w. silus), Sierra Aconchi, Sonora, MX. Photo by Jim Rorabaugh[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][vc_column_inner width=”1/2″][vc_single_image image=”2702″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Young juvenile Ridge-nosed Rattlesnake, Huachuca Mtns. Photo by Jim Rorabaugh[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][/vc_row_inner][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”2704″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Crotalus willardi silus, Sierra El Tigre, Sonora © 2008 Robert Villa / ASDM Sonoran Desert Digital Library[/vc_column_text][/vc_column_inner][vc_column_inner width=”1/2″][vc_single_image image=”2703″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Crotalus willardi willardi, Arizona. Photo by Jim Rorabaugh[/vc_column_text][/vc_column_inner][/vc_row_inner][/vc_column][/vc_row][vc_row][vc_column width=”1/6″][/vc_column][vc_column width=”2/3″][vc_column_text]

Description

Editor’s Note:  Dave Barker (2016, C. willardi species account in the Schuett et al. Rattlesnakes of Arizona book) proposes elevating all five subspecies of Ridge-nosed Rattlesnake to species.  He argues they show predictable geographical variation in color, pattern, scalation, and allozymes, and because populations occur in isolated sky island mountain ranges they are on different evolutionary trajectories.  This new arrangement has not been adopted by the Reptile Database or any other authority of which we are aware.     

Scientific and Nomenclatural History

The first specimen of the Ridge-nosed Rattlesnake (Crotalus willardi) was collected in 1897 on the Smithsonian Institution/United States National Museum of Natural History’s Nelson-Goldman Mexican biological expedition, which lasted 14 years. This specimen was found 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 the summer of 1900, ornithologist Francis Cottle Willard collected the type specimen of C. willardi in the environs of Ramsey Canyon near the Hamburg mine and settlement in the Huachuca Mountains of southeastern Arizona. This type locality was amended from Tombstone, Arizona by ornithologist Henry Swarth in 1921. The snake was in a collection of Willard’s specimens which was acquired by Edmund C. Heller. Ichthyologist Seth Eugene Meek reported on and described the two new species in the collection: the Southern Pacific Rattlesnake (Crotalus [oreganus] helleri) in honor of Heller, and C. 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)”.

Recognized Subspecies

In 1949, Laurence M. Klauber, the late preeminent authority on rattlesnakes, described the 1897 specimen and other later southern specimens as C. w. meridionalis (Southern Ridge-nosed Rattlesnake) in reference to the southern latitude of the subspecies at the southern extent of the species’ range.  In the same paper, Klauber described the nominate subspecies, C. w. willardi (Arizona Ridge-nosed Rattlesnake), and 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 (and likely Chihuahua, minus the Sierra del Nido). There is a known hybrid between wild C. w. willardi and the Banded Rock Rattlesnake (Crotalus lepidus klauberi) (O’Connor, and Malawy, unpub. photos).

In 1959, James D. Anderson collected a specimen of C. willardi from the Sierra del Nido in northwestern Chihuahua.  In 1962, he described this isolated population as C. w. amabilis(Del Nido Ridge-nosed Rattlesnake), in reference to its beauty.

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 that are characteristic of other subspecies. It is found in three mountain ranges on the borders of Arizona, New Mexico, Sonora, and Chihuahua. One documented hybrid from the wild is known between this subspecies and the Banded Rock Rattlesnake (Crotalus lepidus klauberi) (Campbell et al. 1989).

In 1974, Herbert S. Harris Jr. informally described C. w. obscurus in a popular non-peer-reviewed magazine preceding its formal description.  The description minimally met the international requirements of a new species description, occupying the name before its formal description (nomen nudum) which he authored with Robert S. Simmons in a1976 C. willardi monograph.  It may have lacked peer review (of the three listed reviewers, one is deceased, one denies involvement, and the other has not yet been contacted) and was published in the Bulletin of the Maryland Herpetological Society, of which Harris was the chief editor (putative conflict of interest).

While Harris (1974) minimally occupied the name, Harris and Simmons (1976) is a formal description. Compounding the issue is the self-plagarism/-occupation of the name, and many rattlesnake biologists did not accept this taxon, placing it as a variant population of C. w. silus. They likely acknowledged the unique identity of the taxon but rejected the methods of its author(s).  The name gained acceptance when David L. Barker (1992) supported the status of all five subspecies using molecular data. Authors continue to cite between Harris (1974) and Harris and Simmons (1976).  It may be advisable to cite the taxon as such: Harris 1974 (Barker 1992) or Harris 1974 (Harris and Simmons 1976). Complications could have been mitigated had Harris and Simmons renamed the taxon in their 1976 monograph, making C. w. obscurus a synonym.

Description and Natural History

The Ridge-nosed Rattlesnake is a relatively small rattlesnake (adults are > 40 cm SVL, maximum of 67 cm total length) with a distinct raised ridge or crest that borders the snout (namesake). Its coloration matches the fallen leaf litter in its habitat (brown to dusky gray with light cross-bars with dark borders). Placement of white facial stripes (or lack thereof in the obscurus subspecies) distinguish the subspecies, however genetic studies may alter the status of these designations.

This elegant rattlesnake is found in mid to high elevation oak, juniper and pine woodlands of southeastern Arizona, southwestern New Mexico, eastern Sonora, western Chihuahua, Durango and Zacatecas (4,300-8,500’/1,300-2,575 m).  In the 100-Mile Circle, only one subspecies is found – C. w. willardi, which occurs in the mountains of southeastern Arizona and northeastern Sonora.  Two others occur close to the boundaries of the Circle, including C. w. obscurus (isolated mountain ranges in Arizona, Chihuahua, New Mexico, and Sonora), and C. w. silus (isolated mountain ranges and the Sierra Madre Occidental of Sonora, and Chihuahua). The species  likely occurs in other ranges in the region. Its presence in the Chiricahua Mountains remains debated, but as yet no specimens have been vouchered from that range.  It has yet to be found in the woodlands of Sinaloa, Nayarit or Jalisco, but may occur there as future state records.

This snake refuges in loose rock and bunchgrass as it conserves needed humidity. Snakes are relatively inactive during the winter months (occasionally exposing themselves to the sun on warm days), and focus their life cycle around the rainy (monsoon) season. Males combat by raising the anterior part of their bodies vertically, attempting to dominate each other by pressing the opponent to the ground. Courting takes place during the entire active season of late spring to fall, as males are opportunistic while females are selective: breeding from July-August and birthing the following year in those months. Litter size is 2-9 (4-6 average), with neonates up to 8”/20 cm (6.5-7.6”/16.5-19 cm on average). In some instances the tails of young snakes are brightly colored, fading with maturity. While not yet observed, it is hypothesized that like the Banded Rock Rattlesnake (Crotalus lepidus klauberi), the bright tail is used to lure lizards within striking range (caudal luring). Young eat prey of proportionate size: invertebrates (centipedes documented), and young lizards. Venom composition likely changes with maturity to immobilize different and bigger prey items like small rodents and shrews, and birds.

Conservation Status

This snake is threatened by a variety of factors in its habitat; primarily habitat loss from cattle grazing, mining, fire, and climate change. Secondarily is woodcutting, collecting by humans, and ignorant killing. This snake is legally protected throughout its range. It is listed as a species of “Least Concern” by the International Union for the Conservation of Nature (IUCN) “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.” (Hammerson et al. 2007). In México it is federally protected, while in the Unites States it is afforded state and federal protection.  Under Arizona Game and Fish Department regulations, it is illegal to collect or possess a Ridge-nosed Rattlesnake without specific authorization. C. w. obscurus is afforded federal protection, being listed as “Threatened” under the Endangered Species Act due to being found in only 3 documented ranges (possibly a few others) and facing the threats listed above. The Recovery Plan for C. w. obscurus can be found at:

http://www.fws.gov/southwest/es/arizona/Documents/RecoveryPlans/RidgenoseRattlesnake.pdf

Literature Cited/Suggested Reading:

Barker, D. G. 1992. Variation, infraspecific relationships and biogeography of the ridgenose rattlesnake, Crotalus willardi. In J. A. Campbell and E. D. J. Brodie (eds.), Biology of the Pitvipers. Pp. 89-106. Selva, Tyler, Texas.

Barker, D.G. 2016. Ridgenose Rattlesnake, Crotalus willardi (Meek 1906).  Pages 655-699 in G.W. Schuett, M.J. Feldner, C.F. Smith, and R.S. Reiserer (eds). 2016. Rattlesnakes of Arizona, Volume 1. ECO Herpetological Publishing, Rodeo, NM.

Brennan, T. C., and A. T. Holycross. 2006. A Field Guide to Amphibians and Reptiles in Arizona. Arizona Game & Fish Department, Phoenix, Arizona.

Campbell, J. A., E. D. Brodie, Jr., D. G. Barker, and A. H. Price. 1989. An apparent natural hybrid rattlesnake and Crotalus willardi from the Peloncillo Mountains of New Mexico. Herpetologica 45(3): 344-9.

Ernst, C.H., and E.M. Ernst. 2012. Venomous Reptiles of the United States, Canada, and Northern Mexico. Volumes 1 & 2. Johns Hopkins University Press, Baltimore, MD.

Hammerson, G. A., J. Vazquez-Díaz, and, G. E. Quintero Díaz. 2007. Crotalus willardi. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. http://www.iucnredlist.org/details/62253/0. Downloaded on 28 December 2013.

Harris, Jr., H. S. 1974. The New Mexican ridge-nosed rattlesnake. National Parks Conservation Magazine 48(3):22-24.

Harris, H.S., and R.S. Simmons.  1976.  The paleogeography and evolution of Crotalus willardi, with a formal description of a new subspecies from New Mexico, United States.  Bulletin of the Maryland Herpetological Society 12(1):1-22.

Lowe, C. H., C. R. Schwalbe, T. B. Johnson. 1986. The Venomous Reptiles of Arizona. Arizona Game & Fish Department, Phoenix, Arizona.

Meek, S.E. 1905 (1906). An annotated list of a collection of reptiles from southern California and northern Lower California. Field Columbian Museum Publication 104, Zoological Series 7(1):1-19.

Rorabaugh, J.C., and J.A. Lemos Espinal. 2016. A Field Guide to the Amphibians and Reptiles of Sonora, Mexico. ECO Herpetological Publishing and Distribution, Rodeo, NM.

Schuett, G.W., M.J. Feldner, C.F. Smith, and R.S. Reiserer (eds). 2016. Rattlesnakes of Arizona, Volume 1. ECO Herpetological Publishing, Rodeo, NM.

Author:  Robert Villa

For additional information on this species, please see the following volumes and pages in the Sonoran Herpetologist: 1994 Aug:68; 1996 Dec:127; 1999 Apr:38-40; 2001 Jul:74-78; 2007 Sep:97.

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