Arizona Ridge Nosed Rattlesnake

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.

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.

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).