Reproductive biology of the northern Pacific rattlesnake (Crotalus viridus oreganus) in northern Idaho

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Reproductive biology of the northern Pacific rattlesnake (Crotalus viridis oreganus) was studied in snakes from three hibernacula in northern Idaho from 1978 to 1981. More females than males were captured, but an analysis of unbiased samples showed a 1:1 sex ratio. Mature males captured from late March to October carried spermatozoa in at least the distal portion of the vas deferens. Upon first emergence, reproductive females had large yolked ova, up to 35 mm in length. Ovulation occurred from mid-May to mid-June. Parturition occurred over a 30-day period beginning in early September. Males longer than 52 cm snout-vent length (SVL) and with four or more rattles were sexually mature. Most females larger than 55 cm SVL and with five or more rattles were sexually mature. Mean clutch size was 5.5, and clutch size was significantly correlated with female body size. The mean proportion of females reproducing annually varied from 54-77% in the three populations of snakes. Reproductive females had the greatest percentage body fat, followed by nonreproductive females and males. The population of snakes with the highest mean proportion of females reproducing annually (77%) also had significantly larger fat bodies. We concluded that nutrition, as evidenced by the size of fat bodies, is the major factor controlling the frequency of reproduction in females.

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Reference Code: A84DIL01IDUS

Diller, L. V., and R. L. Wallace. 1984. Reproductive biology of the northern Pacific rattlesnake (Crotalus viridus oreganus) in northern Idaho. Herpetologica 40(2): 182-193.

Location: ANIMAL EF: REPTILES