Snakes can respond to variation in resource availability through changes in diet and species interactions. For many species, however, patterns of variation in diet are poorly known. Making use of novel 13C, through the provision of supplemental food in the form of milo (Sorghum spp.) for Northern Bobwhite (Colinus virginianus), we used carbon (δ13C) and nitrogen (δ15N) stable isotope analyses to evaluate the specificity of mammalian and herpetofaunal diet, trophic niche width, and trophic niche overlap between five snake species in the Red Hills of the southeastern United States. Most mammalian prey and Northern Bobwhite were characterized by different δ13C values in the milo- and non-milo-treated areas. Using milo to reflect dietary patterns we determined that Coachwhip (Masticophis flagellum), Cottonmouth (Agkistrodon piscivorus), and Eastern Rat Snake (Pantherophis alleghaniensis) were dietary generalists, revealed by larger isotopic range and lack of correspondence between isotopic values and those of distinct prey groups. In contrast, Black Racer (Coluber constrictor) and Corn Snake (Pantherophis guttatus) were dietary specialists. Black Racers fed largely on herpetofauna, and δ13C values of Corn Snake revealed a gradual ontogenetic/size-related diet shift from herpetofauna to a mammalian-based diet. There was considerable overlap of isotopic trophic niche between snake species, except for the Cottonmouth with δ15N values higher than other sampled species. These findings provide novel insight into snake trophic ecology.
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Vol. 2014 • No. 2