The Santa Catalina rattlesnake (Crotalus catalinensis) is a species of pit viper endemic to Isla Santa Catalina in the Gulf of California just off the east coast of the state of Baja California Sur, Mexico. Like all other pit vipers, it is venomous. No subspecies are currently recognized. A relatively small and slender species, its most distinctive characteristic is that it lacks a rattle. They are also a generally nocturnal species. Though the species is classified as Critically Endangered on the IUCN Red List, there few efforts for the snake's conservation. Description This species is relatively slender and stunted, growing to a maximum of in length. Its most distinctive feature is its lack of a rattle. The base of the tail, the "button", has degenerated to such an extent that the rattle immediately falls off with each shed instead of forming a new segment, as it does in other species of rattlesnakes. This is widely believed to be a localized adaptation for hunting mice as well as occasionally birds. Of the two distinct color variations, the predominant variant has a light cream-colored base, with reddish-brown blotching down the back, and black and white banding around the tail. The other variant has a much lighter, ash gray color, with darker gray blotching. The banding around the tail is still present. The banding tapers off and becomes more obscure. The two different colors were originally thought to be due to natural selection and therefore match different habitat backgrounds, but that has not been supported. There is no difference between the brown and grey within the habitat, as well as no difference in the frequency of color between males and females. However, evidence suggests that the darker coloration on the snakes make them more easily adaptable because of their ability to bask and absorb more heat. This causes their metabolism to speed up which provides them with faster digestion that helps increase strength and physical conditions. Due to these factors, the darker colored snakes have greater reproductive success than the lighter colored snakes. Though the dark snakes have these advantages, their coloration comes at a cost because they are more easily spotted by predators than the sand colored snakes. Geographic range This snake is found only on Isla Santa Catalina in the Gulf of California off the coast of southern Baja California. This island is also the type locality for the species. The