Overview
The Northern Pacific Rattlesnake (Crotalus oreganus) is the only venomous snake native to the vast Pacific Northwest region of Washington, Oregon, and British Columbia. A master of camouflage and arid-land ambush hunting, this heavy-bodied pit viper is famous for its intricate mosaic of dark hexagonal blotches and its interlocking keratin rattle, which buzzes a polite, unmistakable acoustic warning to passing hikers and large ungulates.
Biology and Physical Characteristics
Crotalus oreganus has a stocky, muscular build with heavily keeled dorsal scales and a broad, triangular head distinct from its narrow neck. Its dorsal coloration is highly variable, ranging from olive-grey and sandy-tan to dark chocolate-brown, patterned with a series of dark brown to black hexagonal blotches edged with pale borders that fuse into dark rings near the tail. Its facial pit organs, situated between the eyes and nostrils, detect infrared heat differences as small as 0.003°C.
Behavior and Ecology
A patient ambush hunter, the Northern Pacific Rattlesnake coils alongside rodent trails beneath sagebrush or basalt rock crevices, waiting motionless for ground squirrels and pocket gophers. In autumn, hundreds of individuals migrate from surrounding hunting grounds to communal winter hibernacula (dens) located deep within south-facing fractured basalt talus slopes, where they hibernate together to survive freezing winter blizzards.
Conservation and Human Impact
Classified as Least Concern by the IUCN, Crotalus oreganus is ecologically vital for controlling rodent populations and limiting Lyme disease vectors. While protected from harvest in British Columbia, populations in the western United States face mortality from road traffic and historic human persecution at traditional winter denning sites.
Interesting Factoid
The heat-sensing pit organs of the Northern Pacific Rattlesnake function like built-in military night-vision cameras: they allow the snake to see a detailed thermal image of a warm deer mouse in pitch-black darkness and strike with pinpoint accuracy.