Reproduction, Rookery Use, and Thermoregulation in Free-ranging, Pregnant Crotalus v. viridis

A study of the reproductive biology of pregnant, free-ranging prairie rattlesnakes was conducted in Wyoming from 1982 through 1987. Females reproduced on a flexible superannual cycle. Pregnant females were longer than nonpregnant females, and heavier than nonpregnant females of similar length. Among pregnant snakes, follicle number was positively correlated with increasing body size. Pregnant snakes that had radiotelemetry transmitters surgically implanted early in the active season resorbed follicles, whereas those with transmitters implanted later in the season continued pregnancy through parturition. Movements from hibernacula to rookeries were spatially direct, but often one more or more in duration. Snakes in rookeries were relatively sedentary, frequently shared shelter rocks with pregnant conspecifics, and maintained higher body temperatures than nonpregnant conspecifics that were not in rookeries. Air temperature, date, and microhabitat were important influences on body temperature. Among other potential benefits, residence in rookeries may enhance reproductive success through thermal effects on gestation.