Autecology of the Sidewinder (Crotalus cerastes) At Kelso Dunes, Mojave Desert, California
The sidewinder rattlesnake is found only in the low hot deserts of the southwestern United States and northwestern Mexico. It has adapted to this environment in various ways and thus is able to live under extremely demanding conditions. Previously published information on sidewinders is quite complete in certain respects and totally lacking in others. The present study represents an attempt to integrate the various aspects of sidewinder biology into a more cohesive unit.
A large sidewinder population at Kelso Dunes, Mojave Desert, California, was intensively studied for three years. A number of parameters - physical, clmatic, behavioral and population - were investigated. Activity cycles are most closely tied to thermal regimes and considerably less so to rainfall and wind. An abundance of small mammal burrows on most of the study area provide thermal refugia on hot days and hibernacula during the winter. Because of the insulating properties of sand and the general lack of frost at Kelso, sidewinder hibernacula are probably scattered over the entire study area and appear to be rather superficial. Mating occurs generally in the spring and the young are born alive in early autumn. Whether the sidewinder reproductive cycle is annual or biennial was not determined.
During warm weather sidewinders become active at dusk and may wander over the sand in any direction for over 1200 meters - mostly by sidewinding. The average distance travelled is much shorter, however. This nocturnal wandering probably serves as a dispersal mechanism, since mark and release studies showed no tendency towards homing or territorality. By midnight, however, even the most active sidewinders have formed resting craters and remain coiled therein until sunrise or later.
Among rattlesnakes cratering is a feature unique to sidewinders. During the day the crater serves primarily for thermoregulation and less so for concealment, whereas at night this order of importance is reversed. Sidewinders prey upon any small reptile or mammal they can overpower and may actually do a considerable amount of feeding from ambush during the day. After feeding they become sedentary until digestion is largely completed, shifting position only to warm the food bolus during the day.
Bio-telemetry studies indicated that the rate of heating or cooling may be more important in thermoregulatory behavior than the simple attainment of absolute thermal thresholds. On cool evenings sidewinders often bask on asphalt roads or railroad rails, using these surfaces as sources of reradiated heat.
The sidewinder population is not uniformly distributed on the Kelso study area. More trackways were recorded in dune areas dotted with large clumps of vegetation with stable sand hummocks beneath them. In rockier areas with low vegetation and little sand, sidewinder trackways were few and mostly those of juveniles. This was attributed to inadequate burrows and the general lack of shade in such areas.