Montana Field Guide

Prairie Rattlesnake - Crotalus viridis

Adults have a triangular head, blunt nose, narrow neck, and stout body; they range in length from 15 to 60 inches. The background color above varies from pale green to brown; a series of brown or black blotches edged with a dark and then a light line extends the length of the body. The blotches often merge into rings on the tail. There are also blotches on the sides. The belly is pale yellow to white and lacks blotches. All rattlesnakes have a heat-sensing pit located between the nostril and the eye. The fangs are hollow and hinged, allowing them to be folded back against the roof of the mouth. The tail ends in a rattle that helps warn potential predators of the snake's presence.

No other snake in montana has rattles (see gopher snake and western hognose snake)

Montana Range

Nonmigratory.

Western rattlesnakes favor open and arid country but are also found in ponderosa pine stands and mixed grass-coniferous forests. They are more likely to be encountered on south-facing slopes and in areas with rock outcrops. Rattlesnakes den communally, but range up to 7 miles from the dens during the summer. Females give birth to 4 to 21 young in late summer; the young are marked similarly to adults, but colors are brighter. Rattlesnakes prey on a variety of animals, including mice, ground squirrels, and rabbits (FWP). Gravid females may aggregate at basking sites (rookeries) (Gannon and Secoy 1985). May be most common near broken country and breaks. Land use changes from range to irrigated farmland may adversely affect population (Pendlebury 1977).

2 of 3 collected in N central MT had eaten Peromyscus manic- ulatus (Mosimann and Rabb 1952). In S saskatchewan, 4 collected w/ prey: 2 P. maniculatus; 1 Richardson's ground squirrel, 1 passa- rine (Gannon and Secoy 1984).

In SW Saskatchewan, one hibernaculum contained an estimated 150 ad., plus juv. and YOY in same den. Overwinter weight loss greater for N pop than for S pop; overwinter mortality of YOY may be significant for N population (Gannon and Secoy 1984).

Female probably has 2 yr repro cycle (Gannon and Secoy 1984). Mate late Jul-early Sep (Klauber 1972). Sperm presumed to stay viable overwinter. Parturition late Aug-Sep - ave. yng = 9-10 in S Saskatchewan (Gannon and Secoy 1984).