Wildlife At Risk in British Columbia
A brochure series which will eventually include brochures on other Red 
and Blue listed species, including fish, invertebrates and plants, and on 
ecosystems.  Produced by the Ministry of Environment, Lands and Parks, 
Wildlife Branch, 780 Blanshard St. Victoria, BC V8V 1X4. For copies of 
this brochure, write to the Wildlife Branch. Funded by Corporate 
Resource Inventory Initiative and Ministry of Environment, Lands and 
Parks.
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Why are Western Rattlesnakes at risk?

In Canada, Western Rattlesnakes are found only in southern British 
Columbia, southeastern Alberta, and southwestern Saskatchewan. Their 
distribution range in British Columbia is confined to dry valleys of the 
southern interior. Because of this restricted range, the Western Rattlesnake 
has a small population in B.C.

Many people dislike snakes in general and poisonous ones like the 
rattlesnake in particular. Their reputation for danger, though not 
deserved, has resulted in needless killing of rattlesnakes since the first 
European settlers arrived in the Interior. This drastically reduced 
rattlesnake populations in some areas. In addition, many of the warm 
southern valleys that are home to these snakes have become heavily 
settled. Farms, subdivisions, highways, and other developments have 
destroyed some rattlesnake dens and foraging areas, and many snakes are 
killed by highway traffic. These threats will become more serious as land 
development and human populations increase.

Most rattlesnakes live out their lives near a winter den (hibernaculum), 
and return faithfully to it each autumn. At these sites, where large 
numbers congregate, the snakes are vulnerable to human-caused 
disturbance and killing. This fidelity to traditional dens also means that 
areas where rattlesnakes or their dens have been eliminated will not be 
readily reoccupied.

Rattlesnake populations suffer some natural losses due to predation by 
skunks, hawks, and other predators. Some die of natural causes in their 
dens in winter, particularly the newborn. Studies near Vernon, British 
Columbia showed that only about 25 percent survived their first year of 
life.

This low annual survivorship together with a low rate of reproduction 
means that populations can increase only slowly in size. This makes 
rattlesnake populations particularly slow to recover and vulnerable to 
local extirpation if populations are reduced through human actions.

What is their status?

The distribution of Western Rattlesnakes in British Columbia is fairly well 
known, but little is known about the actual number of dens and total 
number of snakes in the province. Without this information we can’t say 
whether they are increasing or decreasing in abundance.

Many rattlesnake populations in the Vernon area were hunted to near-
extinction in the 1930s and 1940s. The local population now seems to have 
recovered from that destruction, but this took several decades. University 
of Victoria researchers have estimated rattlesnake abundance of 1.5 to 2.5 
snakes per hectare in good habitat near Vernon on study areas where 
several dens occur in close proximity. These numbers cannot be applied to 
other areas because Western Rattlesnakes have such a patchy distribution 
within their range.

Rattlesnakes are legally protected under the British Columbia Wildlife 
Act. This Act prohibits the capture or killing of wildlife, except for the 
protection of life or property. Unfortunately, some people feel that any 
rattlesnake they encounter is a threat and should be killed. In reality, 
rattlesnakes are rather timid and easily avoided.

Because the Western Rattlesnake has a limited distribution in British 
Columbia and is vulnerable to direct killing and habitat loss, the Wildlife 
Branch of BC Environment has placed it on its Blue List. Blue-listed 
species are considered to be vulnerable or sensitive. This listing does not 
provide any additional legal protection, but indicates that the species 
deserves more attention in order to maintain its population in the 
province.

What do they look like?

The Western Rattlesnake (Crotalus viridis) is one of British Columbia’s 
largest snakes; adults are from 60 to 150 centimetres in total length. Two 
other species, the Western Yellow-bellied Racer and the Gopher Snake, 
can equal or exceed this length. Sometimes confused with the Gopher 
Snake because of a similar colour pattern, the rattlesnake is readily 
distinguished by its broad head, which is triangle-shaped and much wider 
than the neck, and the rattle on the end of its tail. Rattlesnakes also have a 
deep pit on each side of the face, between the eye and the snout (most 
safely seen with binoculars).

The background colour is brown, tan, olive or grey, overlaid by large 
dark-brown blotches along the back and smaller blotches along the sides. 
In older animals, the blotches may be surrounded by a white- or cream-
coloured ring. Towards the tail, the blotches appear more like bands 
around the body. There is a broad, dark stripe on each side of the face, 
from below the eye to the corner of the jaw. The underparts are normally 
yellowish-white, but sometimes brownish. Males and females have a 
similar appearance. Juvenile rattlesnakes are usually lighter in colour than 
adults, and show greater contrast between the blotches and background 
colouring.

The common name “rattlesnake” refers to the rattle-like structure at the 
end of the tail. Rattles consist of several horny segments which produce a 
buzzing sound when the tail is vibrated rapidly, and are used to warn 
intruders of the presence of the snake. A new rattle segment is produced 
each time the snake sheds its skin. Because shedding may occur more than 
once a year, and segments at the end of the rattle often wear away, the 
number of rattle segments is not a reliable way to tell the age of a 
rattlesnake. Rattlesnakes grow throughout their life and the largest ones 
are usually the oldest.

What makes them unique?

One of the most noteworthy habits of rattlesnakes, particularly where 
winters are cold, is their use of communal dens for hibernation. Twenty-
four dens which were studied near Vernon contained from 8 to 266 
rattlesnakes per den. All had one, two or three entrances; most were in 
south-facing rock outcrops. Small numbers of other snakes (Western 
Yellow-bellied Racers; Common Garter Snakes; Gopher Snakes) also used 
many of those dens.

Dens are the focal point of rattlesnake activity, and all seasonal 
movements start and end there. In summer, most snakes follow regular 
travel routes to favourite foraging and basking areas up to a kilometre or 
more from the den. Pregnant females however, remain near their dens. 
The snakes almost invariably return to the same den each fall, although a 
few juveniles sometimes switch dens.

Little is known about rattlesnake dens. They are deep enough so that the 
snakes can avoid freezing temperatures. When hibernating, the body 
temperatures of rattlesnakes near Vernon were found to be in the 2 to 7°C 
range, and within one degree of the den temperature.

Rattlesnakes grow throughout life (except while hibernating) and must 
regularly shed their skin, which becomes worn and too small. The old 
skin, shed from the nose backward, is turned inside-out as the snake 
crawls forward out of it. In the North Okanagan area most adults shed 
once per summer; a few shed twice. Most juveniles shed twice. 
Rattlesnakes are more vulnerable than usual during this shedding process, 
which takes about 15 to 20 days, and seek secluded places while it is going 
on.

Western Rattlesnakes are unique in being the only venomous (poisonous) 
snakes in British Columbia (apart from the mildly venomous Night Snake, 
which is not believed to be harmful to humans). In recent years, however, 
the average number of people bitten has been only three or four per year, 
and only one of 63 bites was fatal. Many bites are a result of foolish 
behaviour around rattlesnakes and could be avoided.

How do they reproduce?

In the Okanagan Valley of British Columbia, rattlesnakes mate in August 
or early September, usually near a den. Mated females enter their winter 
dens soon after this with sperm stored in the uterus, but ovulation and 
fertilization don’t occur until after they emerge the next spring. From two 
to eight (average of five) young then develop internally during the 
summer and are born live in September or early October. The total period 
from mating to birth is lengthy – about 13 to 14 months. After giving birth 
the females almost immediately resume hibernation without mating or 
feeding. This means that rattlesnakes in this area can produce young, at 
most, every second year; every third year is more common and some may 
breed even less often than that!

Pregnant females stay near den entrances through the summer, carefully 
regulating their body temperatures by basking in the sun or by seeking 
shade when it is too hot. This ensures a proper temperature for the 
developing embryos. They generally do not feed during this period or 
while hibernating during the following winter, resulting in a fasting 
period of 19 months or more. Females have to double their weight before 
they can breed again, often taking two summers to do this.

Young rattlesnakes, about 30 cm long when born in September, shed their 
skin about three weeks after birth. A “button” develops at the end of the 
tail when the skin is shed. A few days later they den for the winter, 
without having eaten.

Male rattlesnakes are sexually mature at three or four years of age but 
may not actually breed until older than this. Studies have shown that 
female rattlesnakes in British Columbia don’t produce their first litters 
until they are six to eight years old. Maximum lifespan is about 25 years.

Western Rattlesnakes in British Columbia are at the northern extreme of 
the species range. At this latitude they must hibernate for up to seven 
months if they are to survive. The short above-ground period places limits 
on feeding and replenishment of energy stores. As a result, Western 
Rattlesnakes grow more slowly, reach sexual maturity later, and breed less 
often in British Columbia than further south.

What do they eat?

Western Rattlesnakes prey almost entirely on small mammals which they 
catch alive and swallow whole, usually head-first. In the North Okanagan 
area, Meadow Voles, Montane Voles and Deer Mice are the major food 
items, but a total of 10 kinds of mammals and a few small birds have been 
recorded in the diet. Juvenile snakes prey mostly on mice and shrews, 
while adults capture and swallow some surprisingly large animals like 
Red Squirrels, Northern Pocket Gophers, and young Yellow-bellied 
Marmots, as well as mice. The halves of the lower jaw are not sutured at 
the chin. This flexibility, plus expandable ribs and skin, means the snake 
can swallow prey of greater diameter than its own body.

Because their most important prey animals are active from dusk to dawn, 
this is when most rattlesnake foraging also occurs. Rattlesnakes are 
superbly adapted for locating warm-blooded animals in dim light by 
means of infrared heat-sensing organs (loreal pits) located on each side of 
their face. They usually strike the prey with a forward stabbing motion, 
inject venom through their hollow fangs, and then withdraw. The hapless 
prey is immobilized in a matter of seconds. The fangs of rattlesnakes are 
hinged so that they can be erected when capturing prey and folded back 
neatly out of the way at other times. If removed, they grow back in a short 
time. The venom of rattlesnakes acts in two main ways – it causes 
muscular paralysis by blocking nerve conduction, and contains enzymes 
which digest tissues.

Where do they live?

The Western Rattlesnake is one of the most widely distributed snakes in 
North America. It occurs from northern Mexico to southern British 
Columbia, Alberta, and Saskatchewan, and from the coast of California 
inland to Kansas and Nebraska. Summer temperatures are mostly warm 
to hot throughout their range, but it is remarkable that this snake has been 
able to adapt to locations with winter climates as different as Alberta and 
southern California.

In British Columbia, rattlesnakes occur only in the dry southern valleys, in 
the Bunchgrass, Ponderosa Pine, and lower fringes of the Interior 
Douglas-fir zones. They have been recorded in the Okanagan, Kettle, 
Similkameen, Nicola, and Thompson River valleys, and along the Fraser 
in the Lytton-Lillooet area. Throughout this area they prefer dry, usually 
rocky and rugged landscapes with sparse or scattered tree cover. 

Terrain having suitable hibernating sites is important for rattlesnakes. In 
British Columbia this usually involves rocky ridges with crevices or deep 
talus slopes. The crevices must be deep enough for the snakes to escape 
freezing temperatures in winter. Rattlesnakes also need suitable hunting 
and basking areas within a reasonable distance of their dens. Foraging 
sites are usually open grassy areas. Riparian zones (near water) are 
important foraging areas for rattlesnakes, since small mammals are 
usually more abundant there. For basking in the sun, exposed rocky 
ledges are preferred.

What can we do?

The Western Rattlesnake is a fascinating result of thousands of years of 
evolution, wonderfully adapted to its dry, rugged environment. It 
deserves our attention and protection just as much as deer, ducks, 
songbirds and other fauna. Its needs are simple: just a place to live and 
freedom from persecution.

Rattlesnakes are rather shy, retiring creatures which normally depart or 
seek cover when approached by people. If cover is not readily available 
they usually give a warning rattle. The last thing they want to do is bite an 
animal that is too big to swallow! This usually only happens when they 
are stepped on, cornered, handled, or attacked. People who encounter 
rattlesnakes along trails should detour around them and go on their way. 
Rattlesnakes will not chase after people and can not strike beyond the 
length of their body. People frequenting known rattlesnake habitats 
should wear heavy trousers and high boots, avoid putting their hands or 
feet into crevices they can’t see into, and generally be on the lookout for 
snakes. Frequent or lengthy visits to rattlesnake dens should be avoided 
so that interference with normal activities of the snakes is minimized.

Rattlesnakes occur where they do because of a combination of habitat 
factors which include hibernating dens, sunny basking places, scattered 
shrubs for shade, travel corridors, and foraging habitats. Alteration or 
destruction of any of these can be harmful to the snakes. Unfortunately, 
the locations of many British Columbia hibernacula are not well known, 
much less the local distribution of important habitats in their vicinity. In 
general, attempts should be made to protect all den sites and natural 
habitats within a kilometre or so of them.

Agencies such as BC Environment and BC Parks have programs for 
habitat protection and den site monitoring, and to ensure that 
development of highways and other major projects do not harm known 
rattlesnake populations. Assignment of the Western Rattlesnake to the 
Blue List now ensures that it will get more attention with respect to 
inventory and protection. The public can be of assistance by advising the 
nearest BC Environment office about den locations and any possible 
threats to them, by supporting the establishment of protected areas for 
rattlesnakes, and by encouraging greater respect for these misunderstood 
and mistreated reptiles.