Distinguishing Features
Western rattlesnakes are marked
with a pattern of large dark dorsal blotches and smaller lateral
ones on a cream to grey background. It is recognizable by the typical
broad, triangular-shaped head of most rattlesnakes, and by the horny
interlocking segments ("rattle") on the tip of the tail.
The maximum recorded length is 145 cm, but anything over 90 cm (3
ft.) is considered large.(Cook, 1984).
Distribution
Columbia Basin: Found in dry lower
valleys of the southern portion of the Columbia Basin.
British Columbia: For the most part,
rattlesnakes are restricted to the dry lower valleys of the Okanagan
and Thompson river basins with some records from the Kettle, Nicola,
Similkameen and Fraser (Lytton-Lillooet area) valleys (Charland
et al. 1993).
Global: Widespread in western North
America. The Western Rattlesnake ranges from southern Canada south
over most of the western United States to northern Mexico.
Habitat
Western Rattlesnakes are found along
rocky ridges with crevices or talus slopes in the dry bunchgrass
grasslands, open Douglas-fir and ponderosa pine woodlands. They
require crevices deep enough to escape winter's freezing temperatures
during hibernation. These dens are generally found on south or southeast
facing slopes. There is considerable site fidelity shown by this
species with individuals returning to the same den site year after
year (Cannings et al. 1999).
Threats
Direct persecution, road mortality
and habitat loss or degradation all threaten this species. At the
northern limit of its range, reproductive rates are lower than they
are further south, increasing vulnerability (Cannings et al. 1999).
Biology
They den communally, spending about 200 days a
year in the den. When they emerge from the den in the spring the
snakes disperse to foraging and basking areas up to 1.5 km from
the winter den. Gravid females tend to move very little, males move
the furthest. In B.C., Western Rattlesnakes feed on small mammals
found in open grasslands or riparian zones, mainly voles and deer
mice. Exposed rock ledges are used for basking. Females reach sexual
maturity in 5-7 years. They mate in August or September, ovulation
and fertilization occurs the next spring when they emerge from the
den, and the young are born between August and October. The average
litter size is 5. There is considerable variation among dens and
years in overwinter survivorship of the young: 0 - 76% (Cannings
et al. 1999)
