Ecological Significance of Movements and Activity Range for the Sidewinder, Crotalus cerastes

Secor, S

This paper describes the effects of sex, age, and time of year on movements and activity ranges of a desert-adapted viperid snake, the sidewinder (Crotalus cerastes). In the eastern Mojave Desert, male sidewinders traveled (x̄ ± 1 SE = 185.4 ± 17.1 m) significantly farther than nongravid females (x̄ = 122.9 ± 10.1 m) within 24-h periods. This was chiefly a result of lengthy movements by adult males during the spring and fall mating seasons. Subadult sidewinders (2-3 yr old, x̄ = 223.1 ± 25.3 m) moved significantly greater distances than neonates (1-3 months, x̄ = 125.5 ± 22.0 m), juveniles (6 months-2 yr, x̄ = 148.3 ± 14.3 m), and adults (>3 yr, x̄ = 123.8 ± 12.1 m). Movements by all snakes were longest during the summer (x̄ = 191.2 ± 17.7 m). Actual distances traveled averaged more than twice the straight-line distances between the beginning and end of movements, demonstrating the distinct tortuosity of C. cerastes movements. Sidewinders traveled on average 60% of the days monitored during their activity season (April-Oct.), with a resultant mean daily distance traveled of 117.8 ± 11.2 m/day. Although direction of travel was generally random, sidewinders exhibited significant directionality during the fall as they moved eastwardly to the sand-alluvial interface of the study site to overwinter. I speculate that overwintering in rodent burrows at the sand-alluvial interface increases overwintering survival because of decreased likelihood of exposure to freezing subsurface temperatures, greater structural stability of burrows, and lower risk of predation. Activity ranges of C. cerastes, calculated by minimum convex polygon (x̄ = 23.2 ± 2.8 ha) and harmonic mean (x̄ = 20.9 ± 2.6 ha) methods, are among the largest documented for snakes. For this population of sidewinders, there were no significant differences in activity range size between sexes or age classes (subadult vs adult). Core areas of activity (harmonic mean 50% isopleths) averaged 9.2 ± 0.9% of total activity range size (harmonic mean 95% isopleths) and also did not differ in size between sexes and age classes. Activity range size did not correlate with body size (SVL and mass), although it did correlate with the number of locality coordinates used in its calculation. Activity ranges of individual sidewinders overlapped extensively on the study site, and snakes commonly shifted their centers of activity seasonally. Sidewinders moved their activity centers during the fall to the site's sand-alluvial edge and returned to the site's sandy region following emergence from hibernation.

Ecological Significance of Movements and Activity Range for the Sidewinder, Crotalus cerastes

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