||Rattlesnakes are California's only venomous serpents, but they are
also beautiful and fascinating reptiles. I'm not the type to pick them
up — all my viewing is at a very safe distance. Perhaps because I am always
at a distance (or at least try to be!...), I've had trouble identifying
some of them in the southeastern deserts where several species may occur.
According to traditional taxonomy (e.g., Stebbins 2003, Crother et al.
2001) there are just six species, all in the genus Crotalus:
[June 1997; Sequoia NP, Tulare Co.]
|Conventionally, the complex had been regarded as a single species,
with 9 subspecies. Pook et al. (2000) carried out the first phylogeographic
study of the complex, and suggested that three species might be recognisable,
and Ashton & de Queiroz (2001) formally recognised an eastern species
(C. viridis) and a western species (C. oreganus). Douglas
et al. (2002) reviewed the systematics of the western rattlesnake (Crotalus
viridis) complex, using a mtDNA phylogeographic approach, with special
emphasis on the Colorado Plateau, and recognise seven species within the
I have read the Pook et al. (2000) paper [available on line in pdf format] and find it fascinating stuff. They were able to reconstruct a phylogeny from mtDNA and, using a presumed mtDNA clock that has good concordance with known physiogeographic events (e.g., rise of the Andes; rise of the Sierra Nevada) can somewhat trace the history of these rattlesnakes from the Miocene. It seems that the trait of dwarfism arose independently twice, in C. v. nuntius ("Hopi Rattlesnake") and in C. concolor (Midget Faded Rattlesnake); the latter population also independently developed a Mohave-like highly lethal toxin. Certainly geologic events, like the formation of Grand Canyon, separated populations and led to developing species. However, unlike the more recent work by Douglas et al. (2002), they stopped short of going overboard on taxonomy and recommended that Western by split into three species: Prairie C. viridis; Arizona Black C. cerberus; and Western (the rest). Even though they stopped short of splitting the rattlers into 7 species, it is clear to me that there were influenced by the phylogenetic species concept (PSC) that has plagued bird taxonomy (e.g., they quote Cracraft, a primary proponent of this species concept in birds, liberally). I strongly suspect that the Douglas et al. (2002) work is grounded in the phylogenetic species concept. If that is true, I would hope that the more restrained "evolutionary species concept" on which Pook et al. (2000) rely better expresses the mainstream thought. although I fear it is a clone of the PSC. In any event, there is a lot going on with rattlesnake taxonomy!
mentioned the problems I have had in the past trying to identify rattlesnakes
in California. Because the colors of rattlesnakes can be so variably, depending
on their habitat, Stebbins (1966, 1985, 2003) emphasizes scalation patterns
that are damned near impossible to see in live snakes in the field, and
hard to work with even in less-than-crystal-clear photos (i.e., in other
words, my photos). Under I started putting together this page, and John
Sullivan gently put me straight, I had misidentified and mislabeled the
snakes shown above and right. They are, in fact, both different races of
Rattlesnake C. mitchellii [as is the headline species at top
of the page, also misidentified in the field]. Above is the beautiful
Rattlesnake C. m. stephensi [photo May 1988 Willow Wash, Inyo
Co.]; to the right is the much paler and less patterned Southwestern
Speckled Rattlesnake C. m. pyrrhus [photo May 1985 Morongo Valley,
San Bernardino Co.].
One small weakness of the maps in Stebbins' field guides is the lack of county borders, so it was hard to me to see what rattlers occur, for example, in Inyo County. Does Western Rattlesnake make it to the White Mts? Does Mojave Rattlesnake get to Death Valley? These questions were not clearly answered. I just did an on-line search of the specimens held at Museum of Vertebrate Zoology, U.C. Berkeley, and found that the only rattlesnakes in their collection from Inyo Co. are Speckled (the Panamint race) and Sidewinder. This makes things much easier.....
To the left is another photo of the same Panamint Rattler
shown stretched out above. One thing I notice in this shot — and in every
other photo of Speckled Rattlesnake on this page and elsewhere on the web
— is that Speckled Rattlesnake has a really flat and triangular shaped
head. Compare that head shape with the little Northern Pacific Rattlesnake
(below) from Tulare County. The head of Western may be triangular but it
is thick and jowly. I've noted this on a lot of other on-line photos also.
Stebbins' field guides don't mention these shape difference but there is
a very different jizz — a concept birders will recognize — to the heads
of these, and presumably other, rattlesnakes. This character needs more
work but might prove useful
|One rattler that I have found easy to identify in southeastern California is Western Diamondback Rattlesnake [right and below, photos May 1998 near north end Salton Sea, Riverside Co.]. Its a BIG, thick-bodied, broad-headed rattler with conspicuous black-and-white rings before the rattle. I've read some surveys (e.g., Klauber 1972) that found the species to the the commonest snake (not just rattlesnake!) is some parts of southern Arizona (e.g., Organ Pipe Cactus NM). It is said to be an aggressive snake but, despite the look of the photo to the right, I've always kept a fair distance!|
I have yet to see Red Diamondback or Mojave Rattlesnake in the state; it is interesting that Mojave is the rattler that has developed venom that is drop-for-drop some ten times more potent that ordinary rattlesnake venom. These and a wide host of interesting facts about rattlesnakes are found in the classic awork by Klauber (1972; this is the popularized, abridged version of his earlier multi-volume books). In researching this page, I also found the summaries and great photos in Mattison (1996) to be very helpful. That book not only has color photos of all U.S. species, but all the Neotropical species as well.
There are many on-line resources for rattlesnakes, but the "California herps" web site has photos of all of them in this State, with links to much additional information. More nice photos are on John Sullivan's "Wild Herps" web site.
Ashton, K.G. & A. de Queiroz. 2001. Molecular Systematics of the western rattlesnake, Crotalus viridis (Viperidae), with comments on the utility of the D-Loop in phylogenetic studies of snakes. Molecular Phylogenetics & Evolution 21:176-189.PHOTOS: All photos © 2003 Don Roberson, all rights reserved. Specific details are in the main text above.
Crother, B.I., chair. 2001. Scientific and standard English names of amphibians and reptiles of North America north of Mexico, with comments regarding confidence in our understanding. Committee of Standard English and Scientific Names, Society for the Study of Amphibians and Reptiles, Herpetological Circular 29 (as supplemented in Herp. Review 32: 152-153).
Douglas, M. E., M.R. Douglas, G.W. Schuett, L.W. Porras & A.T. Holycross. 2002. Phylogeography of the western rattlesnake (Crotalus viridis) complex, with emphasis on the Colorado Plateau, pp. 11-50 in G.W. Schuett, M. Höggren, M. E. Douglas and H. W. Greene (eds.), Biology of the Vipers. Eagle Mountain Publ., Eagle Mountain, UT.
Klauber, L.M. 1972. Rattlesnakes: Their Habits, Life Histories, and Influence on Mankind. Abridged ed. by K.H. McClung. Univ. of Calif. Press, Berkeley. Publ. for Zoological Soc., San Diego.
Mattison, C. 1996. Rattler! A Natural History of Rattlesnakes. Blandford, London.
Pook, C.E., W. Wüster & R.S. Thorpe. 2000. Historical biogeography of the western rattlesnake (Serpentes: Viperidae: Crotalus viridis), inferred from mitochondrial DNA sequence information. Molecular Phylogenetics & Evolution 15: 269-282.
Stebbins, R.C. 1966. A Field Guide to Western Reptiles and Amphibians. Houghton Mifflin, Boston.
Stebbins, R.C. 1985. A Field Guide to Western Reptiles and Amphibians. 2d ed. Houghton Mifflin, Boston.
Stebbins, R.C. 2003. A Field Guide to Western Reptiles and Amphibians. 3d ed. Houghton Mifflin, Boston.
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