AMBUSH SITE SELECTION OF A DESERT SNAKE (ECHIS COLORATUS) AT AN OASIS

The selection of an appropriate ambush site by a sit-and-wait predator is necessary for maintaining an adequate energy intake for survival and for future reproduction, especially when events are of long duration. We tested whether the snake Echis coloratus (Viperidae), a sit-and-wait predator, selects specific ambush sites in an oasis setting. We characterized the sites used by 22 individuals near a desert spring and compared them to randomly selected available sites. Ambush sites were not random; they were usually located <5 m from water on raised objects. Females, but not males, occurred more frequently under cover than expected by random choice. Field observations did not enable us to determine the cues that lead the snakes to locate their ambush. Thus, we used semi-natural enclosures to test the hypothesis that E. coloratus uses prey chemical cues when selecting its ambush sites. Most ambushes were located in sites with cover, whether the odor of gerbils was present or not. Even when odors from additional prey species were presented, there was no preference for sites with odor over control sites. The results suggest that E. coloratus at the oasis set ambushes in microhabitats that provide cover, high probability for encounters with prey, and, possibly, a physiologically convenient humid environment. The cues used by E. coloratus for predicting future prey availability seem to be the structure of the microhabitat rather than prey odor.