Crotalus mitchellii

Crotalus mitchellii
Conservation status
Least Concern Least Concern  (IUCN 3.1)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	Squamata
Suborder:	Serpentes
Family:	Viperidae
Genus:	Crotalus
Species:	C. mitchellii
Binomial name
Crotalus mitchellii (Cope, 1861)
File:Crotalus mitchellii distribution (RDB).png
Synonyms
Caudisona mitchellii Cope, 1861 C[rotalus]. mitchellii — Cope In Yarrow In Wheeler, 1875 [Crotalus oreganus] Var. mitchellii — Garman, 1884 Crotalus mitcheli [sic] Belding, 1887 (ex errore) Crotalus Mitchellii [mitchellii ] — Stejneger, 1895 Crotalus mitchelli — Boulenger, 1896 Crotalus aureus Kallert, 1927 Crotalus tigris mitchellii — Amaral, 1929 Crotalus confluentus mitchelli — Klauber, 1930 Crotalus mitchelli mitchelli — Klauber, 1952 Crotalus mitchellii mitchellii — McCrystal & McCoid, 1986

Common names: speckled rattlesnake, Mitchell's rattlesnake, white rattlesnake

Crotalus mitchellii is a venomous pit viper species in the family Viperidae. The species is native to the Southwestern United States and adjacent northern Mexico. The species was named in honor of Silas Weir Mitchell (1829–1914), an American medical doctor who also studied rattlesnake venoms. Two subspecies are recognized as being valid, including the nominate subspecies described here.

Description

Generally, Crotalus mitchellii does not exceed 100 cm (39 in) in total length (tail included), with large males measuring between 90 and 100 cm (35 and 39 in). The race on Isla Ángel de la Guarda is known to become larger, the maximum recorded length for a specimen there being 136.7 cm (53.8 in). In contrast, the population on El Muerto Island only reaches a maximum of 63.7 cm (25.1 in) in length. On the back are about thirty sometimes vague markings often in the form of crossbars. The speckled rattlesnake is sometimes erroneously called the tiger rattlesnake because of these markings. Other times the markings are clearly defined geometric shapes – diamonds, hexagons, hourglasses – which vary in color from snake to snake but are always darker than the ground color. Normally there is a community coloration based on the snakes' specific rock setting. The whole effect: an individual snake looks like it had been formed from granite, a protective coloration it uses with great effect, and that is also quite beautiful when examined, as one might a work of art, against a contrasting background.

Geographic distribution

Crotalus mitchellii is found in the southwestern United States and in northwestern Mexico. In the US, its range includes east-central and southern California, southwestern Nevada, extreme southwestern Utah, and western Arizona. In Mexico, it is native in northwestern Sonora and most of Baja California, including Baja California Sur. It also inhabits a number of islands in the Gulf of California, including Angel de la Guarda Island, Carmen, Cerralvo, El Muerto, Espíritu Santo, Monserrate, Piojo, Salsipuedes, and San José, as well as on Santa Margarita Island off the Pacific coast of Baja California Sur.

The type locality is listed as "Cape St. Lucas, Lower California" (Cabo San Lucas, Baja California Sur, Mexico).

Habitat

The preferred natural habitat of Crotalus mitchellii is rocky desert and shrubland.

Behavior

Crotalus mitchellii is terrestrial, but will sometimes climb into low vegetation.

Reproduction

Crotalus mitchellii is ovoviviparous.

Subspecies and taxonomy

Subspecies	Taxon author	Common name	Geographic range
C. m. mitchellii	(Cope, 1861)	San Lucan speckled rattlesnake	Mexico, in Baja California Sur and on the islands of Santa Margarita, Cerralvo, Espíritu Santo, San José, Monserrate, and Carmen
C. m. muertensis	Klauber, 1949	El Muerto Island speckled rattlesnake	Mexico, on the island of Isla El Muerto

Grismer (1999) argued that C. m. angelensis and C. m. muertensis should be given species status, mainly due to differences in body size. More recently, Douglas et al. (2007) recognised C.m. stephensi as a full species, and Meik et al. (2015) elevated both the southwestern and the Angel de la Guarda speckled rattlesnakes to the state of full species, C. pyrrhus and C. angelensis, whereas the El Muerto Island speckled rattlesnake was considered part of C. pyrrhus

Conservation status

The nominate subspecies (Crotalus mitchellii mitchellii) is classified as "Least Concern" on the IUCN Red List of Threatened Species. The population trend was stable when assessed in 2007. 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.

Further reading

• Cope, E.D. (1861). "Contributions to the Ophiology of Lower California, Mexico and Central America". Proceedings of the Academy of Natural Sciences of Philadelphia 13: 292–306. (Caudisona mitchellii, new species, pp. 293–294).
• 129 pp. (Crotalus mitchelli [sic], pp. 40–41).
• 240 pp. (Crotalus mitchelli [sic], pp. 206–207).
• 533 pp., 56 color plates. (Crotalus mitchellii, p. 412 + Plate 51 + Map 193).
• 1,105 pp. (in two volumes). (Crotalus mitchelli [sic], pp. 974–977, Figure 278 + Map 68 on p. 971).

External links

• Crotalus angelensis at San Diego Natural History Museum
• Crotalus mitchelli at San Diego Natural History Museum
• Crotalus mitchellii pyrrhus