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Prairie Rattlesnake

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.

In general, the distribution of Prairie Rattlesnakes appears to be closely associated with major rivers. The majority of records from Alberta occur along the South Saskatchewan River drainage (including the South Saskatchewan, Red Deer, Bow, and Oldman Rivers) and the Missouri River drainage which includes the Milk River. Away from the river valleys, the relative abundance of the Prairie Rattlesnake decreases.