BEHAVIORAL VARIATION IN NATURAL-POPULATIONS .6. PREY RESPONSES BY 2 SPECIES OF GARTER SNAKES IN 3 REGIONS OF SYMPATRY

Diets and congenital reactions to prey were studied in the garter snakes Thamnophis elegans and T. sirtalis at three sites where they occur in sympatry in northern California and Washington. Recently ingested prey retrieved from the stomachs of wild-caught snakes indicated that T. sirtalis was primarily an anuran predator at all three sites. In contrast, T. elegans was primarily a slug predator at two sites, but at a third site leeches, anurans and fish dominated the diet. Congenital reactions to prey were studied by measuring chemoreceptive responses to prey odours by naive, newborn snakes. Within each snake species, chemoreception scores showed litter differences within localities as well as geographical variation. Geographical differences in chemoreceptive responses generally coincided with geographical differences in diet, suggesting evolutionary responses to selection. © 1992 The Association for the Study of Animal Behaviour.