Feeding ecology of the desert nightsnake, Hypsiglena torquata (Colubridae)

We studied the diet of the North American desert nightsnake, Hypsiglena tor quata, based on the stomach contents of 397 museum specimens, field observa tions, 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 amphisbaeni ans. Lizards are typically swallowed head- first, whereas frogs are swallow ed from the rump. Prey mass increases with snake mass and prey/predator mas s 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 ar ose within a Neotropical clade of predominantly nocturnal, frog-eating snak es, and its occupancy of arid western North America correlates with two der ived feeding traits: at least occasional ambush predation on diurnal lizard s, and inclusion of squamate eggs in its diet.