Forward attack modes of aquatic feeding garter snakes

Abstract

Summary Previous studies have suggested that piscivorous snakes generally use sideways head sweeping to capture prey in order to minimize drag on the skull and/or to avoid pushing prey items away from the mouth. However, some aquatic species of garter snakes (genus Thamnophis) have been reported to use fast forward strikes to capture fish and amphibians. To characterize fast forward striking as a mode of piscivory in snakes and compare its use among specialist and generalist species, the aquatic specialists Thamnophis couchii and T. rufipunctatus, and a terrestrial generalist, T. sirtalis, were filmed at 250 fps (frames per second) while preying on minnows. Both T. couchii and T. rufipunctatus oriented visually toward prey items and struck forward rapidly with peak head velocities that approached speeds attained by fast striking booid, colubrid and viperid species on land. In contrast, T. sirtalis did not orient visually toward specific prey items and displayed strikes that were four to six times slower than those of specialist species. Aquatic specialists used moderate amounts of cranial rotation during jaw opening and achieved maximum gape within 20 ms of jaw opening. In the generalist T. sirtalis, jaw opening took 40–60 ms and was due almost entirely to mandibular rotation. Significant differences in the prey capture kinematics of the two aquatic specialists are consistent with the hypothesis that T. couchii is an open water hunter, whereas T. rufipunctatus is an ambush predator. Thamnophiine snakes display a diversity of aquatic prey capture styles that reflect different behavioral and mechanical solutions to the problem of feeding in water.