Arboreal ambush site selection by pit-vipers Gloydius shedaoensis

For a sit-and-wait predator, the choice of ambush site may be a crucial determinant of foraging success. During fieldwork on a small island in northeastern China, we explored the availability and use of arboreal ambush sites (tree branches) selected by Shedao pit-vipers, Gloydius shedaoensis. The snakes were highly selective at a variety of spatial scales. For example, they displayed strong biases in terms of which tree species were used, which individual trees within each species were used and which branches were used within a tree. Snakes disproportionately used trees that were on the edge rather than the interior of thickets, and branches that faced out towards the clearing rather than back towards the thicket. Branches at an angle slightly above horizontal were preferred. The snakes used branches visited at high rates by potential prey, that provided effective camouflage, and with thermal and visual backgrounds (cool, bright) that contrasted strongly with avian prey items (hot, dark). The snakes used perches close to the ground (the area of greatest bird activity) despite suboptimal visual and thermal backgrounds. Use of thicker branches by larger snakes, and by snakes containing recently ingested prey items, may contribute to effective camouflage. Thermoregulation did not appear to influence foraging site selection.