Diet and Foraging Behaviors of Timber Rattlesnakes, Crotalus Horridus, in Eastern Virginia

—During a 17-yr telemetry study, we examined the diet and ambush behavior of a population of Crotalus horridus in southeastern Virginia. Forty dietary items were identified from 37 fecal samples. We documented 722 instances of snakes in an ambush posture, 61% of which were in a vertical-tree posture, as if hunting arboreal prey at the base of a tree. The most common prey items were Eastern Gray Squirrels (Sciurus carolinensis), which accounted for 45% of all dietary items and represented an estimated 78% of total biomass consumed by C. horridus. Prey was not consumed in proportion to availability, based on small mammal surveys. Our analysis provides indirect evidence that the vertical-tree foraging behavior is adopted to target arboreal Eastern Gray Squirrels. Further, we provide support for the hypothesis that C. horridus alters ambush behavior to forage selectively for specific prey types. Knowledge of predator–prey relationships and related foraging behaviors is important to understanding snake evolution and can provide the basis for studying broader ecological questions (Mushinsky, 1987). The diet of predators is likely influenced by a number of interrelated factors, including habitat structure (Mullin and Mushinsky, 1995; Mullin and Cooper, 1998; Reinert et al., 2011), relative sizes of prey and predator (Shine, 1991; Arnold, 1993), prey availability (Reinert et al., 1984; Capizzi et al., 1995; Beaupre, 2008), and temporal (Santos et al., 2000; Willson et al., 2010) or geographic (Kephart, 1982; Kephart and Arnold, 1982) variation in prey species. Strategies used by predators that result in the selection of prey with specific taxonomic affinities may lead to closely linked relationships between predator and prey. If prey selection is occurring, foraging behaviors of predators are expected to correlate with movement patterns and microhabitat selection of prey; however, understanding the foraging ecology of a species requires details of both foraging behaviors and diet. Information on the composition of snake diets has been slow to accumulate because most snakes are cryptic, solitary, and eat infrequently (Zaidan and Beaupre, 2003; Clark, 2006), and virtually all obligatorily ingest prey whole (Greene, 1997), such that no remains can be observed. As a result, the known diet of a snake species often is the compilation of anecdotal records gathered from across its distribution. Such an approach may mask the detection of interpopulation variation in diet (Rodriguez-Robles, 2002) and may be problematic when ascribing associations between diet and behaviors related to prey acquisition. Snakes are classified as either active or sit-and-wait foragers (Schoener, 1971). Active foragers constantly move through the environment to locate prey, whereas sit-and-wait foragers ambush their prey from fixed locations; however, even sitand-wait foragers must actively search for ambush locations. The degree to which sit-and-wait foragers actively search for ambush locations varies by species along a continuum from those that select new ambush sites frequently, ‘‘mobile ambushers’’ such as Crotalus viridis (Reinert et al., 1984), to those that relocate to new ambush sites infrequently, such as bushmasters, Lachesis stenophrys (Greene and Santana, 1983). Sitand-wait foragers may select ambush sites based on the detection of prey movements or odors (Reinert et al., 1984; Duvall and Chiszar, 1990; Theodoratus and Chiszar, 2000) or on microhabitat structure (Shine and Li-Xin, 2002; Tsairi and Bouskila, 2004). Because sit-and-wait predators rely on prey movements to initiate encounters (C. H. Greene, 1986), a premium is placed on identifying sites that are frequently used by prey species, such as the runways of small mammals or trees heavily used by arboreal species. For sit-and-wait generalist predators, such as Timber Rattlesnakes (Crotalus horridus), the location of ambush sites is expected to correlate with prey selection and, therefore, with diet. Crotalus horridus occupy a wide variety of habitats, from high-elevation deciduous forests of the Appalachian Mountains, to lowland forests of the southeastern coastal plain, and grassland prairies of the Midwest (Conant and Collins, 1998). The diet of C. horridus includes mainly small mammals, but occasionally, birds also are consumed (Clark, 2002). Employing chemosensory cues to locate small mammal runways along sticks and fallen logs, C. horridus will lie motionless with the body coiled and the head positioned perpendicular to the runway (Reinert et al., 1984). Non–log-oriented posture facilitates catching small mammals on the open forest floor. Alternatively, C. horridus will coil at the base of a tree, often with the anterior portion of its body looped against the tree and its head oriented vertically (Brown and Greenberg, 1992). Interestingly, geographic variation in foraging behaviors occurs, because not all tactics are observed in all populations studied (Waldron et al., 2006; Reinert et al., 2011; Wittenberg, 2012). We investigated the association between foraging posture and diet of C. horridus to better understand their natural history. During a long-term radiotelemetry study at a lowland forest site in southeastern Virginia, we frequently observed snakes ambushing at the base of live trees in the vertical-tree position described by Brown and Greenberg (1992), which led us to hypothesize that snakes adopted this posture to ambush tree squirrels. Herein, we test the prediction that vertical-tree ambush posture targets Eastern Gray Squirrels (Sciurus caroCorresponding author. Present address: Department of Biological Sciences, Auburn University, Auburn, Alabama, USA. E-mail: goetz@ auburn.edu Present address: Department of Biology, Utah State University, Logan, Utah, USA DOI: 10.1670/15-086 linensis). To do so, we compared diet, determined through fecal analysis, to the frequency of ambush postures observed during the telemetric study of this population. In our study, a positive relationship between time spent in the vertical-tree ambush position and squirrel remains in snake feces would indicate squirrels are the target of the vertical-tree ambush position. Specifically, we assess the diet of our C. horridus population as it relates to foraging posture and relative prey abundance and