Seasonal and diel activity patterns in two sympatric desert snakes: Saharan sand viper and crowned leaf nose
The Saharan Sand Viper (Cerastes vipera) and the Crowned Leafnose (Lytorhynchus diadema) are two snake species well adapted to sand desert dunes and, in Israel, coexist in the western Negev desert. Both species are relatively small, prey on, lizards, and are active at night during the warm season. Although C. vipera is a sit-and-wait ambusher while L. diadema is an active hunter,, they inhabit the same niche and are, presumably, in competition We questioned how these species co-exist and studied the seasonal and diel activity patterns of these two species while free living in the field. Field observations and capture of the snakes were carried out in 14 consecutive years in the sand dunes surrounding Wadi Seher in the Negev desert-Israel, in an area populated by both species. Activity level of adults only was measured by recording the markedly divergent tracks of each species. An index of activity was calculated by dividing the number of individuals observed each night by the number of hours invested per observation. We compared activity levels among months and between C. vipera and L. diadema.
Results showed that both species were active from early spring until late fall but displayed: (1) different seasonal activity patterns - C. vipera was bimodal with peaks in spring and autumn whereas L. diadema was basically unimodal with a peak in summer; (2) different nocturnal above ground activity patterns - C. vipera was active mainly during the first three hours of darkness while L. diadema was active during the first seven hours of darkness; and (3) different patterns of distance travelled - C. vipera moved up to 50 m. while L. diadema moved several hundred meters each night. We concluded that temporal partitioning in above-ground activity and seasonal and nocturnal behavioral differences may contribute towards the coexistence of the two species.