Ambush site selection and ontogenetic shifts in foraging strategy in a semi‐aquatic pit viper, the Eastern cottonmouth

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 semiaquatic 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.

Ontogenetic shifts in ambush-site selection of a sit-and-wait predator, the Chacoan Horned Frog (Ceratophrys cranwelli)

“…Selection of foraging sites is the product of a trade-off driven by food availability and the cost, or perceived cost, concomitant with those sites (Werner et al 1983;Lima and Dill 1990;Schalk et al 2010;Eskew et al 2009). In this study, we observed an ontogenetic niche shift in the form of ambush-site selection, between metamorphs and adults of C. cranwelli.…”

“…The selection of habitat sites by an individual is a product of many interacting factors, including morphological and physiological constraints. Patterns of habitat selection by individuals reflect access to resources (e.g., food), risks of competition and predation, and any number of ecophysiological factors (Eskew et al 2009;Schalk et al 2010). As body size increases during ontogeny, importance and strengths of these interacting factors shift, resulting in the ability of individuals to use different habitats and food resources.…”

Habitat influences diet overlap in aquatic snake assemblages

“…However, a more intensive study employing different capture methods at one fishless wetland suggested that Ag. piscivorus also feeds heavily on Ambystoma in those habitats (Eskew, Willson & Winne, 2009).…”

Strike mechanics of an ambush predator: the spearing mantis shrimp

“…The predator must avoid detection (Bailey, 1986;Kral et al, 2000;Bilcke et al, 2006;Eskew et al, 2009), attain high accelerations and speeds (Cooper et al, 1985;Alfaro, 2002;reviewed in McBrayer and Wylie, 2009), and retain some control over strike kinematics (van Leeuwen et al, 2000;Deban et al, 2001). To achieve these goals, ambush predators use three strategies to capture prey: (1) concealment through burrows or camouflage, (2) quick traverse of a potentially large distance to prey and (3) rapid attack to impact prey before escape.…”