Revista Chilena de Historia Natural 65:485-493,1992 The feeding behavior and natural history of two Chilean snakes, Philodryas chamissonis and Tachymenis chilensis (Colubridae) La conducta alimentaria e historia natural de dos culebras chilenas, Philodryas chamissonis y Tachymenis chilensis (Colubridae) HARRY W. GREENE and FABIAN M. JAKSIC Museum of Vertebrate Zoology, University of California, Berkeley, California 94720, U.S.A.;and Departamento de Ecologia, Universidad Catolica de Chile, Casilla 114-D, Santiago, Chile ABSTRACT Philodryas chamissonis, maximum length ca. 2.2 m, feeds on anurans, lizards, birds, rodents, and rabbits; constriction is used for killing endothermic prey. An ontogenetic dietary shift is demonstrated by smaller individuals eating only ectothermic prey. Tachymenis chilensis, maximum length ca. 0.7 m, feeds only on anurans and lizards and does not exhibit an ontogentic dietary shift. Both species are diurnal hunters and typically swallow prey head-first. Prey /predator mass ratios are not especially large compared to other snakes. There is widespread sympatry and considerable overlap in diet, but T. chilensis eats more anurans and extends into cooler, moister habitats than does P. chamissonis. The low species richness of snakes in Chile appears to result from geographic isolation rather than ecological limits on inter- specific coexistence. Key words: Diet, food habits, feeding behavior, Chile. RESUMEN Philodryas chamissonis, longitud maxima ca. 2,2 m, se alimenta de anuros, lagartijas, aves, roedores y conejos; usa cons- triccion para matar las presas endotermicas. Un cambio ontogenetico en dieta se demuestra con los individuos pequei'ios predando s lo presas ectotermicas. Tachymenis chilensis, longitud maxima ca. 0,7 m, se alimenta s lo de anuros y lagar- tijas y no muestra un cambio ontogenetico en dieta. Ambas especies son cazadoras diurnas y tfpicamente ingieren sus presas con Ia cabeza por delante. Los cuocientes de masa presafpredador no son particularmente grandes en compara- cion a otras culebras. Hay una extensa simpatria y sobreposicion en dieta entre estas culebras, pero T. chilensis come m s anuros y se extiende hacia habitats m s frfos y humedos que P. chamissonis. La baja diversidad de culebras en Chile parece ser el producto de aislamiento geografico antes que de lfmites impuestos porIa coexistencia interespecifica. Palabras claves: Dieta, bitos alimentarios, conducta alimentaria, Chile. INTRODUCTION Lineages and faunas that have indepen- dently achieved similar characteristics provide natural experiments for examining questions about adaptation (e.g., Jaksic 1981; Donoghue 1989) and species rich- ness gradients (e.g., Schall & Pianka 1978; J aksic & Delibes 1987). Snakes possess several attributes that make them good candidates for such broader purposes (Arnold 1972; Vitt 1987), and detailed (Received 10 April1992; accepted 14 October 1992 .) case studies also are crucial for under- standing the evolution of feeding in these highly unusual reptiles (Ananjeva & Orlov 1982; Greene 1983, 1989, in press; Savitz- ky 1983; Voris & Voris 1983). In the present paper we analize the geographic distribuci6n and diets of Philodryas cha- missonis (Wiegmann) and Tachymenis chi- lensis (Schlegel), two poorly known and particularly interesting South American colubrids. We discussed elsewhere the roles of Chilean snakes as prey for and potential