E-Fauna BC: Electronic Atlas of the Wildlife of British Columbia

Crotalus oreganus (Holbrook, 1840)
Northern Pacific Rattlesnake; Western Rattlesnake
Family: Viperidae

Species account author: Karl W. Larsen and Jessica Gosling.

Photo of species

© David Shackleton  Email the photographer   (Photo ID #2867)

E-Fauna BC Static Map
Distribution of Crotalus oreganus in British Columbia
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Species Information

The Western Rattlesnake is the only member of the viper family and the only venomous species found in British Columbia. It is easily distinguished from other snake species in the province by the presence of the rattle (a series of modified, interlocking scales on the end of the tail) and sensory heat pits along the upper lip. However, the rattle is not always present, particular in young animals that may not have grown enough and added enough segments onto the rattle in order to generate the buzzing sound or in an older animal where the segments have been broken or damaged. A series of blotches run down the back, developing into more ring-like patters towards the tail. The blotches take on various shapes, particular towards the tail, but tend to be rather square. The animal also has a flattened, triangular-shaped head with a more distinct neck than the other snakes. In British Columbia, the colour of the animal is usually a mixture of greys, olive greens, and darker shades, with whiter bands separating the blotches. Young animals often show more vibrant, brownier tones. In general, the animal appears bulkier and more robust than the other snakes in the province, although for its size, the musculature is relatively less developed than the other snakes.

This is not a large rattlesnake compared to other North American species. Extremely large males can exceed 110 cm from the tip of the snout to the end of the tail, although individuals like this very rare, possibly because the animals rarely live long enough to attain this size.

Biology

Reproduction

Western rattlesnakes in B.C. have a fascinating reproductive life-cycle. Females give birth to live offspring (i.e. they do not lay eggs) in late summer. The energy put into producing the litter normally results in the mother being very emaciated; if the female is fortunate, she may obtain a meal prior to the onset of hibernation in autumn. The following summer is normally spent feeding and attempting to regain body mass. Females may then breed the following summer (i.e. two years after the previous reproductive bout) but they also may require yet another one or two summers to reach reproductive condition. When the female is ready to breed again, she will mate in the mid-part of the summer, but will not allow the eggs she is carrying to become fertilized. Instead, the sperm is maintained in the oviduct over the subsequent winter, and the eggs become fertilized in the following spring. The young are born later on. Litter sizes vary, depending on the size and condition of the female. Small females may only have one or two pups, whereas larger females will produce more.

By comparison, life is easy for the adult males: They leave their den (hibernating site) in the spring, will mate during the summer, and then return to the den in autumn.
Diet

The Western Rattlesnake preys primarily on small mammals, such as mice, voles, and chipmunks. They are also known to take juveniles or nestlings of larger species, such as marmots. Birds are also occasionally taken. Juvenile rattlesnakes further south (i.e. in the USA) are known to prey on lizards, but as lizards are a rarity in the grasslands of BC where rattlesnakes live, the young rattlesnakes probably have to rely on raiding nests or taking very young small mammals. Shrews may also be important. This restriction of dietary items for young rattlesnakes in BC may place a constraint on populations of the animals.
Behaviour

The denning behaviour of rattlesnakes is one of the most interesting behaviours exhibited by the animals. Because of our latitude, suitable denning sites that provide protection from freezing winter temperatures likely are relatively scarce, so this requires the snakes to be very adept at returning to their original denning sites each autumn. Individuals likely occasionally switch dens, but this appears relatively rare: rattlesnakes tend to be ‘hardwired’ to return to the same den each fall. How young rattlesnakes locate a hibernating site after being born is not truly understood.

Another notorious behaviour shows by rattlesnakes is their defensive posturing when threatened. If cornered or threatened, a rattlesnake will coil with a distinctive S bend in its neck. However, rattlesnakes are relatively timid animals, and may not even rattle or assume a defensive posture unless threatened or cornered. Often, their first defense is to remain motionless and undetected. Rattlesnakes cannot ‘leap’; rather, they can only strike within about one third of their body length. Unlike the gopher snake, another snake in BC that acts more aggressively when threatened, rattlesnakes do not ‘hiss’ when threatened, although may breath loudly and dramatically as a warning.

Rattlesnakes are not easy to locate, especially after they have left their denning sites in the spring. They are cryptic animals, often tucking themselves into crevices or other retreat sites. During hot summer days, they may become more active towards night-time, or early in the morning.

Habitat


Rattlesnakes are primarily associated with the dry, semi-arid grasslands of the southern extremes of British Columbia. Denning sites tend to be at the lower elevations in the hottest valleys of the province (eg. Thompson, Okanagan, etc.), so early in the spring, this is where the animal is most usually encountered. However, recently, radio-tracked rattlesnakes have ventured higher up in the valleys than one would expect, taking them into lower-elevation forests during the hottest part of the summers.

Distribution


Western rattlesnakes range from British Columbia in the north to Baja California in the south. They can be found as far east as Utah, Idaho and Arizona. The subspecies of rattlesnake which occurs in BC extends south through Oregon state and into northern California.

As mentioned, these animals are found within the hotter, drier valleys of southern BC. They range from Lytton in the west and north to Kamloops. They are found throughout the Okanagan valley from the border to Vernon, and through the Boundary region of Grand Forks and Christina Lake.

Globally, there are many species of rattlesnakes, found primarily in North and Central Americas, although some species extend into the northern half of South America.

Conservation


Rattlesnakes are an amazing and important part of our native grassland fauna, and the animals should be left alone unless they are clearly posing a threat. As mentioned above, the likelihood of encountering a rattlesnake while hiking is unlikely, but when it occurs, people should simply stop walking, determine where the animal is, and then move away. Rattlesnakes will not pursue people, as is commonly thought. Keeping rattlesnakes (and all native BC fauna) as pets is not permitted. Report any situations of people keeping rattlesnakes in captivity to a local Conservation Officer.

Taxonomy


Until recently, the scientific name of these animals was Crotalus viridis oreganus. This meant that rattlesnakes in BC and the prairies of Canada were considered the same species. Molecular research in the early 2000s showed that these two groups of snakes could be traced back to a historic ‘split’ in the rattlesnake clade of the western USA, and this resulted in the Western Rattlesnake being renamed as Crotalus oreganus oreganus. There are other subspecies or ‘races’ of Crotalus oreganus, but only C. o. oreganus is found in BC. This re-labeling of the animal essentially ‘created’ a new species of rattlesnakes in Canada, and in doing so, placed more focus on the status of rattlesnakes in BC.

Comments


The Danger of Rattlesnake Bite: Much of the fear and persecution of rattlesnakes is due to the fact they are our only venomous species. Certainly, the animal deserves respect and should never be handled. In the event of a bite, the victim should remain calm (insect bites kill more people each year in North America than snakes), and be transported to a medical facility as quickly as possible. Rattlesnake bites normally show up as two small puncture holes side-by-side (from the two front fangs of the animal). Different opinions exist as to how bites should be treated, so leave this up to a medical professional. The venom of the Western Rattlesnake is not nearly as potent as that of many other venomous snakes, including some other rattlesnake species. The severity of the bite depends on many factors, such as the age, size and health of the victim, and the location of the bite. Again, let medical professionals decide on the best course of action.

Take steps to prevent rattlesnake bites when hiking within the range of the animal, in a fashion analogous to being cautious when in bear country. Stay on trails, and always look where your hands or feet are going. Don’t wear sandals – stick with good footwear, and don’t wear shorts – even light pants have been shown to sometimes reduce the amount of venom that a rattlesnake may inject when biting a person on the leg. Young rattlesnakes do not have more or less toxic venom than adult snakes, and although they may inject relatively less venom than a larger animal, anyone bitten by even the smallest rattlesnake should immediately seek medical attention.

The important thing to remember is that these are timid animals, and with common sense and precaution, we can minimize danger to both humans and snakes.

The Rattle of the Rattlesnake: The rattle of these snakes is one of their more fascinating features. Many snakes vibrate their tail when threatened (like the gopher snake), but only the rattlesnakes have evolved a device that actually makes noise. Why and how this adaptation came about is not clear. We do know that each time an animal sheds it adds another segment to the rattle. But, because snakes do not necessarily shed once per year (it may be more, or less), and because rattles also break off from time to time, the number of segments on a rattle is only a rough guide to the age of the animal.

Status Information

Origin StatusProvincial StatusBC List
(Red Blue List)
COSEWIC
NativeS2S3BlueT (May 2015)
BC Ministry of Environment: BC Species and Ecosystems Explorer--the authoritative source for conservation information in British Columbia.

Additional Range and Status Information Links

Additional Photo Sources

General References


Recommended citation: Author, Date. Page title. In Klinkenberg, Brian. (Editor) 2021. E-Fauna BC: Electronic Atlas of the Fauna of British Columbia [efauna.bc.ca]. Lab for Advanced Spatial Analysis, Department of Geography, University of British Columbia, Vancouver. [Accessed: 2022-08-07 9:25:35 PM]
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