Common English names: Santa Catalina Rattlesnake,^[2] Santa Catalina Island Rattlesnake^[3]

Crotalus catalinensis is a species of venomous pitviper endemic to Isla Santa Catalina located in the Gulf of California just off the eastern coast of the state of Baja California Sur, Mexico. No subspecies are currently recognized.^[4] A relatively small and slender species, its most distinctive characteristic is that it lacks a rattle.^[2]

Description

This species is relatively slender and stunted, growing to a maximum of 73.1 centimetres (28.8 in) in length.^[2]

The most distinctive feature about this species of rattlesnake is that it has no rattle at all. The base of the tail, referred to as 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 rattlesnake. This is widely believed to be a localized adaptation for hunting birds.^[3]

There are 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 grey color, with darker grey blotching. The banding around the tail is still present.

Geographic range

Found only in western Mexico 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.^[1]

Conservation status

This species is classified as Critically Endangered (CR) on the IUCN Red List of Threatened Species with the following criteria: B1ab(v) (v3.1, 2001).^[5] This means that the best available evidence indicates that it is considered to be facing an extremely high risk of extinction in the wild because its geographic range is estimated to be less than 100 km², it exists at only a single location, and a continuing decline has been observed, inferred or projected in the number of mature individuals. Year assessed: 2007.^[6]

It is threatened due to collecting and the introduction of alien predator species, such as feral cats.^[3]

Habitat

The habitat on Santa Catalina Island consists of Gulf Coast Desert plants. This snake is often found on the western side of the island within the many arroyos.^[3]

Behavior

While most members of this genus are almost entirely terrestrial due to their heavy body structure, this species' small size makes it a swift and skillful climber. Previous researchers hypothesized that the ability of C. catalinensis to climb, combined with its lack of a rattle allowed it to hunt roosting birds. ^[3] However detailed research into the species’ diet has revealed that C. catalinensis maintains a mammal-based diet like most rattlesnakes. ^[7] Further inquiry into the arboreal behavior of this island species has revealed that individuals actually spend the majority of their time on the ground. ^[8] Individuals were most likely to be found in low branches of bushes during July, the hottest month on the island. There is speculation that C. catalinensis climbs off of the hot ground and into bushes to thermoregulate. ^[9] Unlike most species of rattlesnake, C. catalinensis, is often observed exposed; it does not tend to hide. ^[10] Currently, the greater evidence supports the theory that the Catalina rattleless rattlesnake has evolved away from having a rattle because it has no need for a warning mechanism against predators. ^[11]

Feeding

Previous theories ^[3] suggested that the tendency for this rattlesnake to climb into low bushes was connected to a dietary shift toward consuming birds. However, studies conducted from 2002 to 2004 revealed that stomach and fecal contents were 70% mammal (Santa Catalina deer mouse, Peromyscus slevini) and 30% lizard species (Santa Catalina desert iguana, Dipsosaurus catalinensis; Santa Catalina side-blotched lizard, Uta squamata; and Sceloporus lineatulus.) “We found no bird remains in scats or stomach contents of C. catalinensis in any year or season.” ^[12]

Taxonomy

Klauber (1972) suggests that this species is closely related to C. scutulatus. However, a later study by Murphy and Crabtree (1985) used allozyme data to conclude that it shares its most recent ancestor with C. ruber. Most of the morphological, biogeographic and biochemical data suggests the same.^[2]

See also

• List of crotaline species and subspecies
• Crotalus by common name
• Crotalus by taxonomic synonyms
• Crotalinae by common name
• Crotalinae by taxonomic synonyms
• Snakebite

References

Further reading