Feeding Ecology of the Desert Nightsnake, Hypsiglena torquata (Colubridae)

Abstract

We studied the diet of the North American desert nightsnake, Hypsiglena torquata, based on the stomach contents of 397 museum specimens, field observations, and published dietary records. Based on 92 prey from throughout much of its distribution, H. torquata, feeds mainly on sceloporine lizards and squamate eggs and occasionally eats frogs, snakes, insects, and amphisbaenians. Lizards are typically swallowed head- first, whereas frogs are swallowed from the rump. Prey mass increases with snake mass and prey/predator mass ratios range from 0.03 to at least 0.50. Three genera of abundant lizards (Cnemidophorus, Coleonyx, Xantusia) are infrequently eaten, which suggests that these lizards chemosensorily avoid desert nightsnakes. Hypsiglena arose within a Neotropical clade of predominantly nocturnal, frog-eating snakes, and its occupancy of arid western North America correlates with two derived feeding traits: at least occasional ambush predation on diurnal lizards, and inclusion of squamate eggs in its diet.