Ambush site selection and ontogenetic shifts in foraging strategy in a semi-aquatic pit viper, the Eastern cottonmouth
E. A. Eskew, J. D. Willson, and C. T. Winne
University
of Georgia’s Savannah River Ecology Laboratory, Aiken, SC, USA
Abstract:
Although habitat selection has been studied in a variety of snake taxa,
little is known about habitat selection in aquatic snake species. Additionally,
due to their small size and secretive nature, juvenile snakes are seldom
included in habitat selection studies. The Eastern cottonmouth Agkistrodon
piscivorus is a semi-aquatic pit viper known to use ambush, sit-and-wait
foraging strategies. Ambush hunters are likely to select habitats that
increase opportunity for successful prey capture while minimizing predation
risk and maintaining appropriate thermal and hydric conditions. We characterized
the foraging strategy and microhabitat use of cottonmouths at Ellenton
Bay, an isolated Carolina bay freshwater wetland on the Savannah River
Site in SC, USA. We measured habitat characteristics of 55 ambush sites
used by 51 individual cottonmouths located during nighttime visual surveys,
as well as 225 randomly selected sites within our search area. Cottonmouths
exhibited an ontogenetic shift in foraging strategy with juveniles using
predominately ambush foraging around the edge of the wetland while adults
were most often encountered actively moving within the wetland. Principal
components analysis revealed that juveniles selected foraging microhabitats
that were different from random and consisted of mud substrate with sparse
vegetation, whereas adults occupied a greater variety of microhabitats
that did not differ from random. Concomitantly, free-ranging cottonmouths
exhibited ontogenetic shifts in diet: juveniles consumed mostly salamanders,
while adults ate a greater variety of prey including other snakes and
birds. Our results highlight the importance of understanding how ontogenetic
changes in coloration, diet and predation risk influence foraging strategy
and microhabitat selection in snakes.
Keywords: Agkistrodon piscivorus, habitat selection, ontogeny,
diet, snake, juvenile
SREL Reprint #3099
Eskew, E.
A., J. D. Willson, and C. T. Winne. 2009. Ambush site selection and ontogenetic
shifts in foraging strategy in a semi-aquatic pit viper, the Eastern cottonmouth.
Journal of Zoology 277(2009): 179-186.
