Santa Catalina Island rattlesnake  (Crotalus catalinensis)

Classified as Critically Endangered (CR) on the IUCN Red List (1).

One of the most notable features of the Santa Catalina Island rattlesnake, and in contradiction to its name, is the lack of a functioning rattle (2). This is believed to be an adaptation for stealth, enabling this rattlesnake to slink silently towards prey (2) (3). It has a relatively slender and short body, with a triangular head distinctly separated from the neck. The Santa Catalina Island rattlesnake may be one of two colour forms (2); the most common form has a light brown or reddish-brown body, patterned with darker diamond-shaped markings, each diamond having a dark and then light border. The less frequently seen colour form is ashy-grey with darker grey markings (2) (4). It has elliptical pupils and, unlike other snakes living in the same region, a heat-sensing pit situated between the nostrils and eyes (2).

This highly threatened snake occurs only on Santa Catalina Island, an island covering just 40 square kilometres, situated in the Gulf of California off the coast of Mexico (1).

Santa Catalina is a rather barren island (5), consisting of rocky hillsides separated by narrow, sandy, dry creeks, known locally as arroyos (1). The Santa Catalina Island rattlesnake occurs mainly in these arroyos, where there is abundant vegetation (1) (2), but may also sometimes be found beneath roots and rocks on the hillsides, or in open areas of sandy soils (1).

While the Santa Catalina Island rattlesnake is a largely nocturnal snake (1), this can vary depending on the time of the year. During spring, when temperatures are a little cooler, the Santa Catalina Island rattlesnake can be observed crawling about during mid-morning as well as at night, while during the heat of summer, this snake is rarely seen out during the day, possibly spending most of the daylight hours in a burrow (2).

Unlike many rattlesnakes, this species is known to be an agile and capable climber. It can move rapidly across the ground, and then swiftly climb into vegetation, to escape danger or to pursue prey (2). It was once thought that its climbing ability, as well as lack of functioning rattle, was an adaptation to eat birds (2). However, more recent research has revealed that the majority of this snake’s diet is comprised of the Santa Catalina deer mouse (Peromyscus slevini), with the remainder consisting of lizards (3). So although this argues against the theory that the lack of a rattle is for silently hunting birds in vegetation, it could have evolved to allow the rattlesnake to hunt these partially arboreal rodents instead (3).

Very little is known about reproduction in this snake. Males have been observed bobbing their heads and flicking their tongues during courtship (5), and evidence suggests that the breeding season falls between spring and early summer, with young being born in late summer to early autumn (2).

Once thought to be a common species, the Santa Catalina Island rattlensnake has suffered declines, primarily due to the killing and illegal collection of individuals; unfortunately its reported passive behaviour makes it an easy target (1). On Santa Catalina Island, ‘pit fall’ traps have been found and people have been seen collecting reptiles in bags. In addition, predation by feral cats, and a decline in the Santa Catalina Island rattlesnake’s main prey, the deer mouse, may pose a threat to this now Critically Endangered species (1).

There are currently no conservation plans in place for this highly threatened reptile. Like many other snakes, this species may receive less conservation attention than it deserves due to long-standing and fairly widespread negative attitudes towards snakes (4). The implementation of a program to control the population of feral cats on the island has been suggested as a measure to help secure the survival of this rare and fascinating snake (1).

View information on this species at the UNEP World Conservation Monitoring Centre.

For further information on the conservation of reptiles see:

• International Reptile Conservation Foundation:
  www.ircf.org