Of the eight subspecies of the Western Rattlesnake
(Crotalus viridis) in North America, the Prairie Rattlesnake, is the only one found in Alberta. The Prairie Rattlesnake varies in distribution and abundance throughout its range. In Alberta, for example, the Prairie Rattlesnake is a
"Blue-listed" species, indicating that it may be
at risk and susceptible to habitat disturbance, population decline, or reductions in provincial distribution.
The habitat of the Prairie Rattlesnake in Canada has been described as mixed-grass prairie, or as short-grass prairie. Low precipitation, high summer temperatures, and a short growing season characterize the semi-arid climate of the mixed-grass prairie, whereas the short-grass prairie occurs under even drier conditions or intense grazing pressure.
In Alberta, the Prairie Rattlesnake is found within the
Grassland Natural Region, often associated with river and
coulee bottoms, badlands, sage flats, and less commonly on open short-grass prairie.
Hibernacula, which allow the Prairie Rattlesnake to survive through long cold winters, are a critical component of Prairie Rattlesnake habitat in northern climates. Slump blocks, meander scarps, subterranean water channels, rock outcrops, and mammal burrows have all been found to provide suitable conditions for hibernacula. Hibernacula are usually found on south-facing slopes which provide maximum solar insulation, while offering protection from
prevailing winds. However, a small number of dens appear to be located on, or adjacent to, east- or north-facing slopes. Overwintering dens of the Prairie Rattlesnake are with other species such as Bull Snakes and Garter Snakes.
Rattlesnakes return to their dens each fall, and therefore hunting and basking areas must be available within a reasonable distance from the
hibernaculum. Another potential habitat requirement of the rattlesnake is the presence of a suitable birthing area or rookery where gravid females can aggregate until parturition. Although only a small number of rookeries have been found, these areas have some common features, including the presence of large, flat table rocks overlaying abandoned mammal burrows. It has been suggested that these habitat characteristics provide quick escape from predators as well as appropriate microhabitat for thermoregulation.
It has been estimated that over two-thirds of the original mixed-grass prairie has been destroyed. This loss, in combination with increased grazing and the construction of roadways and pipelines on the prairies suggest that the availability of suitable habitat for Prairie Rattlesnakes may be declining in the province.
Snake populations in cold climates often develop specific behavioral and physiological strategies for dealing with a shortened active season. In Alberta, Prairie Rattlesnake populations reach the northern limit of their distribution, and restrictions imposed by the colder climate should be reflected in their thermal
Knowledge of activity patterns in rattlesnakes may also be critical for understanding habitat requirements. During the active season, rattlesnakes may migrate long distances from their overwintering dens.
In the spring, migration appears to be associated with a search for suitable foraging areas.
Reprinted from Alberta Wildlife Status Report No.
with permission from Alberta
Sustainable Resource Development.