In snakes, like all ectothermic reptiles, body temperature (Tb) is dependent mainly on the environmental temperature (Te), especially the temperature of the substrate (Ts) in contact with the individual. In sub-tropical zones, Te can vary widely, both daily and annually. The Saharan sand viper (Cerastes vipera) is a relatively small snake, up to 35 cm in length, is mostly nocturnal, and is limited to sand and desert dune systems from the Atlantic coast of North Africa to Israel on the east. In Israel, it inhabits the western Negev Desert. C. vipera is active from spring to autumn and hibernates during winter. Mating season is short, up to two weeks, from the end of April to the beginning of May. It is mainly a sit-and-wait ambusher, preying primarily on diurnal lizards of the Acanthodactylus genus. Rodent burrows and burrowing under bushes provide shelter from high temperatures during the day. We tracked the thermal behavior of C. viperaand, concomitantly, measured air, substrate and body (cloacal) temperatures.
C. vipera were active at Ts as low as 13°C at night during the mating season and as high as 48°C during morning activity, when buried in the sand in ambush position. Night activity began with sand basking before dusk soon after exiting the day shelter. This behavior consisted of characteristic burrowing, and included a mixing of sand of different temperatures, presumably to achieve a suitable Tb for activity. During night activity, Tb was usually 2-5°C higher than Ts. Night activity of many C. vipera ended by entering a rodent burrow or burrowing under a bush. We observed other individuals burrowing themselves some 30-40 cm from a rodent burrow, with heads towards the entrance, leaving only eyes and nares slightly above the sand surface. They stayed buried 8-10 hours, until 11:00 next morning, when Acanthodactylus lizards were active and C. vipera had the opportunity of foraging. When Tb approached 42 °C, the C. vipera literally jumped into the rodent burrow, presumably to avoid over-heating. Such flexible physiological and behavioral adaptations to a wide Ts range allow C. vipera to adjust its foraging potential for both nocturnal and diurnal activity and to maximize prey availability in the harsh desert environment.