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New Mexico Ridgenosed Rattlesnake

Crotalus willardi obscurus

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Species Description

The New Mexico ridgenosed rattlesnake (Crotalus willardi obscurus) is a captivating and elusive species found in the rugged landscapes of the southwestern United States, particularly in the state of New Mexico and extending into the sky islands of Mexico. Belonging to the larger group of ridgenosed rattlesnakes, this subspecies showcases unique characteristics that distinguish it from its counterparts.

Typically measuring between 1 to 2 feet in length, the New Mexico ridgenosed rattlesnake boasts a slender and elegant build, adorned with intricate patterns and coloration that provide excellent camouflage amidst its rocky desert habitat. Its dorsal scales often feature a series of dark bands or blotches, interspersed with lighter hues of tan, gray, or brown, blending seamlessly with the surrounding terrain.

As a master of stealth and ambush, this rattlesnake species is predominantly nocturnal, preferring to hunt under the cover of darkness when temperatures are cooler and prey activity is heightened. Its diet primarily consists of lizards, which it captures using its potent venom and specialized heat-sensing pits located on either side of its head, but they also will prey on small mammals, centipedes, and passerine birds.

Range

Rautsaw, R.M., Jiménez-Velázquez, G., Hofmann, E.P. et al. VenomMaps: Updated species distribution maps and models for New World pitvipers (Viperidae: Crotalinae). Sci Data 9, 232 (2022). https://doi.org/10.1038/s41597-022-01323-4

Currently, there are three known isolated populations of the New Mexico ridgenosed rattlesnake subspecies. These populations are situated in the Animas Mountains in New Mexico, the Peloncillo Mountains spanning both New Mexico and Arizona, and the Sierra San Luis Mountains in Mexico. The species is extremely rare in the Animas and Peloncillo Mountains. Remarkably, these three populations are confined to just three of the approximately 57 sky-islands within the region.

The Madrean Sky Islands, also referred to as the Madrean Archipelago, represent a biodiversity hotspot extending across northwestern Mexico and the southwestern United States, encompassing regions of Arizona and New Mexico. Characterized by pine and oak forested mountains encircled by low elevation desert and grassland expanses, these sky islands serve as unique ecological havens. The principles of island biogeography often find relevance in understanding the dynamics of these sky islands.

Species Status

The New Mexico ridgenosed rattlesnake is critically endangered and is one of only two species of rattlesnake protected under the Endangered Species Act. The species is also state protected in New Mexico and Arizona. 

Climate change and habitat loss are the primary threats to this species, as increasingly frequent wildfires alter the distribution and availability of suitable habitat for the species. Vegetation structure important for supporting the species take decades to recover after wildfire events and forestry activities. Shifts in temperature and precipitation patterns, along with increased frequency and intensity of wildfires, pose significant challenges to the New Mexico ridgenosed rattlesnake's ability to persist in its native range.

Furthermore, the small population size and limited genetic diversity of the New Mexico ridgenosed rattlesnake render it particularly vulnerable to stochastic events and demographic fluctuations. Inbreeding depression and genetic bottlenecks further compound the species' susceptibility to extinction.

In addition to habitat loss and climate change, direct threats such as illegal collection continue to impact populations of the New Mexico ridgenosed rattlesnake. Unlike other species of rattlesnake, due to their rarity and the lack of urban development within their range, the species does not face a primary threat of indiscriminate killing by humans. 

Despite these challenges, there is cause for hope in ongoing research and conservation efforts aimed at mitigating threats and promoting the recovery of the New Mexico ridgenosed rattlesnake. By implementing evidence-based management strategies informed by scientific research and the latest population assessments, we can work towards ensuring the long-term survival of this unique and ecologically important species.

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