Natural History and Morphology of Crotalus ehecatl (Serpentes: Viperidae)

The Tehuantepec Isthmus rattlesnake (Crotalus ehecatl) is a poorly known species endemic to Mexico. We describe its diet, morphological variation, life history traits and activity patterns based on data from field encounters, museum specimens, and published data. Its diet consists almost exclusively of mammals, with no detected ontogenetic shift or sexual differences in prey type, and with feeding happening mainly in the rainy season. As the first detailed study on the feeding ecology of C. ehecatl, it adds six new prey species and suggests a homogeneous diet among age classes and sexes, but not among seasons. Crotalus ehecatl does not present sexual dimorphism in snout-vent length, head length or total length, but males have significantly longer tails than females, possess fewer ventral scales, more subcaudal and anterior intersupraocular scales. Crotalus ehecatl showed a unimodal activity pattern with peak activity in the summer, with crepuscular and nocturnal activity during the warmer months, and diurnal activity during the cooler months. The timing of C. ehecatl reproductive events, is similar to other rattlesnakes from temperate and tropical zones. Additional studies on this and related species would help to understand how the ecology of Neotropical rattlesnakes differs from rattlesnakes of more temperate zones.