Abstract

Crotalus catalinensis is a rattleless rattlesnake endemic to Santa Catalina Island, in the Gulf of California, Mexico. It has been hypothesized that the lack of a rattle in this species is a stealth adaptation for hunting birds in vegetation. We provide detailed data on the diet of C. catalinensis from samples obtained during nine trips to the island in 2002–2004. Over two-thirds (70%) of the diet of C. catalinensis was composed of the Santa Catalina Deer Mouse (Peromyscus slevini). The remaining prey were lizards (Dipsosaurus catalinensis, Uta squamata, and Sceloporus lineatulus). There was an ontogenetic shift in diet and higher feeding activity during the dry season. The diet of this species is only a small subset of the diet of its supposed closest relative, C. ruber, probably as a result of limited diversity of prey on the island. The lack of birds in the diet of C. catalinensis argues against the supposed importance of birds as an essential feature for the hypothesis relating the lack of a rattle with a stealth hunting technique for birds in vegetation. However, since P. slevini is partially arboreal, there remains the possibility that the lack of a rattle is an adaptation for stealth hunting for mice in vegetation.