Santa Catalina Island Rattlesnake

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 are few efforts for the snake's conservation.

Description

This species is relatively slender and stunted, growing to a maximum of 73.1 cm (2 ft 4.8 in) in length.

The most distinctive feature of this snake 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, as the rattle becomes a liability rather than an asset while hunting. The lack of any large predators or hoofed mammals in its natural locale has also played a factor in making the rattle redundant. It appears that Crotalus catalinensis may not be alone in feeling these selective pressures, as red diamond rattlesnakes on the island of San Lorenzo Sur and San Esteban island black-tailed rattlesnakes also appear to be losing their rattles. Notably, it appears that this phenomenon is confined to populations limited to islands in the Gulf of California.

Natural selection has also given this snake a more elongated body than featured in related mainland forms, and measurably longer teeth; These are both characteristics associated with snakes that hunt in trees and shrubs such as this species. This species also lacks the standard bite-and-release tactic employed by usual rattlesnakes, preferring to instead hold prey in its jaws until the venom can take effect. In this way, it avoids the possibility that prey might fall out or fly away prior to succumbing.

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