David Cundall

CHAPTER 9 – Feeding in Snakes

Body elongation and limblessness have evolved significantly within Tetrapoda, typically associated with aquatic, fossorial, crevice dwelling, or grass-swimming lifestyles. Some lineages of secondarily elongate vertebrates (for example, limbless skinks) have solved the concomitant problem of reduction in size of the feeding apparatus by eating many tiny items, whereas others (for example, some caecilians) shear ingestible chunks out of large prey. Many advanced snakes achieved a third solution by radically restructuring their heads and feeding infrequently on large items; perhaps not coincidentally. Among limbless squamate reptiles, only Serpentes has achieved substantial adaptive radiation and high species richness. More than 2,500 species of living snakes inhabit most temperate and tropical land masses, and they often are prominent predators in terrestrial, arboreal, fossorial, aquatic, and even marine faunas. Snakes eat prey as different as onycophorans, fish eggs, centipedes, cormorants, and porcupines; many species commonly consume individual items weighing 20% of their own mass, and some venomous species occasionally subdue and eat prey that exceed their own mass by as much as 50%. This chapter first briefly surveys snake diversity and then examines in detail the functional and morphological aspects of capturing, swallowing, and processing prey that generally characterize relatively derived subgroups. It only touches on sensory aspects of feeding.

Foraging behavior of the timber rattlesnake, Crotalus horridus

moregulation of lizards and toads at high altitudes in Peru. Copeia 1976:155-170. POUGH, F. H., AND C. GANS. 1982. The vocabulary of reptilian thermoregulation, p. 17-23. In: Biology of the Reptilia. Vol. 12. C. Gans and F. H. Pough (eds.). Academic Press, New York. SIEGEL, S. 1956. Nonparametric statistics for the behavioral sciences. McGraw-Hill, New York. TRACY, C. R. 1975. Water and energy relations of terrestrial amphibians: Insights from mechanistic modeling, p. 325-346. In: Perspectives in biophysical ecology. D. M. Gates and R. B. Schmerl (eds.). Springer-Verlag. New York. . 1976. A model of the dynamic exchanges of water and energy between a terrestrial amphibian and its environment. Ecol. Monogr. 46:293-326. ZWEIFEL, R. G. 1955. Ecology, distribution, and systematics of frogs of the Rana boylei group. Univ. Calif. Publ. Zool. 54:207-292.

Morphology and behavior of the feeding apparatus in Cryptobranchus alleganiensis (Amphibia: Caudata)

Cine and high‐speed videographic analyses of feeding in Cryptobranchus alleganiensis demonstrate that prey are captured by either inertial suction or a strike combined with suction. Movements of cephalic elements during capture are generally similar to those of other suction‐feeding vertebrates but more variable than those of most aquatic salamanders. Following capture, prey frequently are manipulated and transported into and out of the buccal cavity across the teeth.

The feeding apparatus of the salamander Amphiuma tridactylum: Morphology and behavior

Anatomical studies of cephalic bones and muscles combined with cine and high‐speed videographic analyses of feeding demonstrate that Amphiuma tridactylum uses two distinct types of suction feeding. Small or relatively immobile prey generally elicit a stationary capture mode in which mouth opening precedes buccal expansion and there is no forward movement of the head of the salamander. Actively moving prey are captured by a rapid strike during which mouth opening and buccal expansion are synchronous and the extent of buccal expansion is greater than in stationary feeding. Differences between these feeding modes may be due to differences in the timing of contraction of the rectus cervicis muscle. Synchronous hyoid and mandibular excursions during the strike are probably generated by simultaneous contractions of the depressor mandibulae and rectus cervicis, whereas delay of hyoid excursions during stationary capture suggests sequential contraction of the depressor and rectus cervicis.

Rhinokinetic snout of thamnophiine snakes

Radiographic and cinegraphic behavioral data, combined with anatomical evidence, indicate that the snout in Nerodia and Thamnophis consists of four movable elements (1, premaxilla; 2, paired nasals; 3, right septomaxilla and vomer; and 4, left septomaxilla and vomer), a condition we refer to as rhinokinetic. In thamnophiine snakes, movements of the snout bones allow the teeth of the right and left sides to separate further and increase the effective stroke distance of each palatomaxillary cycle during swallowing.

Spatial Biology of Northern Watersnakes (Nerodia sipedon) Living along an Urban Stream

Abstract Fifty Nerodia sipedon living along two kilometers of an urban stream in northeastern Pennsylvania were radio-tracked over three activity seasons, yielding more than 2520 relocations. Half the stream length is urbanized, flowing through a city park at the head of the study area and an industrial area at the downstream end; the half between is relatively natural, flowing through a conservation corridor. Individual snakes exhibited high site fidelity. For 82% of relocations, snakes were within a one-meter radius of places they had previously occupied, most often using exactly the same hole, rock, branch, or cover object. Snakes were found to have moved to a different site at 27% of relocations. When snakes moved, they returned to previously occupied places 56% of the time. Females exhibited significantly greater site fidelity than males, and snakes occupying the urban half of the study site exhibited significantly greater site fidelity than snakes found in the natural half. Individuals varied greatly in the amount of space they utilized. Snakes had a mean minimum convex polygon (MCP) activity area of 1.13 ha. Snakes appeared to use the stream to travel between locations separated by more than 100 meters. Original MCPs overestimated space use by including large terrestrial areas that were never occupied by and were unsuitable to snakes. Fixed kernel methods underestimated space use by producing multiple small, disjunct contours. Both methods often largely or completely excluded the stream. To address these problems, we provide additional estimates of space use that sum the MCPs encompassing all of a snakes locations within 100 meters of each other and add the area of stream connecting the most upstream and downstream locations.

Striking Patterns in Booid Snakes

Striking is kinematically variable in booid snakes but generally fits one of three patterns. Analysis of slow speed, short-exposure video records of more than 200 strikes in 17 juveniles and subadults of seven species of booids shows that they first hit the prey either with the mandibles (MAN strikes) or with the mandibles and upper jaw together [driving scissors (DSC) strikes], rarely with the upper jaw [palatomaxillary (PMX) strikes]. In MAN strikes, inertia carries the braincase over the prey in an arc whose radius is partly defined by the tip of the mandible. In DSC strikes, both jaws slide over the prey. In both of these strike patterns, much of the impact of prey contact appears to be directed through the mandibles and their suspensoria and adductor muscles. Ventral flexion of the whole head and neck initiates the first constricting coil shortly after contact with the prey and may be aided by reaction forces generated by the preys inertia. In PMX strikes, on the other hand, the braincase incurs a higher proportion of impact forces and ventral flexion of the head is often delayed. The predominant use of MAN and DSC strikes suggests that these kinematic patterns in combination with tooth geometry may reduce the probability of tooth breakage at the time of jaw impact with the prey. The same tooth geometry increases the probability of snaring in the interval between contact and immobilization by constriction.

HABITAT USE BY SYNURBIC WATERSNAKES (NERODIA SIPEDON)

Abstract We examined habitat use in a population of synurbic watersnakes with equal access to urban and natural habitats to test the hypotheses that species occupy urban environments either by (1) restricting their activities to any remaining natural areas, or (2) capitalizing on, instead of avoiding, artificial features. For three years we radio-tracked 50 northern watersnakes (Nerodia sipedon) living in a 40-ha area along 2 km of a city stream in Pennsylvania (USA). Half the study site is urbanized (municipal park and an active industrial area), and half is a relatively natural conservation area. Habitats selected by snakes in the two areas were significantly different: in the natural half, snakes occupied areas with a wide riparian zone and dense canopy cover; in the urban half, they frequently used artificial substrates and were in close proximity to people. Snakes were relocated 2520 times, yet were found at only 113 sites. Frequently reused sites were mostly artificial, including piles of scrap metal or concrete, holes in a railroad bed adjacent to the stream, and dead evergreen trees secured into the stream bank to combat erosion. Urban and natural areas were approximately equal in area and stream length, and had similar numbers of snake-selected sites (64 urban, 49 natural), but urban sites were used by more snakes. Of sites used by more than five different snakes, 22 of 26 were in the urban area. Snakes were found within 5 m of a tagged conspecific at 38% of urban area relocations compared to 15% of natural area relocations. These data suggest that anthropogenic structures in urban environments provide conditions (concealment, thermal) that offset dangers posed by closer proximity to people.

Viper Fangs: Functional Limitations of Extreme Teeth*

The fangs of vipers are extremely long, rotating, hollow teeth. Analysis of video records of more than 750 strikes recorded at 60 or 250 frames per second for 285 individuals representing 86 species in 31 genera shows that vipers reposition fangs after initial contact with prey in more than a third of the strikes. Repositioning resulted when fangs missed prey entirely or hit prey regions that did not permit adequate penetration. The prevalence of repositioning, even among species that normally release prey, suggests strong selective pressure for rapid neuromotor response to fang placement error. The rapidity of repositioning suggests the existence of (a) fine‐scale sensory detection of fang penetration depth, (b) rapid modulation of contraction of antagonistic muscles, and (c) possibly neurological modifications to shorten transmission time between sensory input and motor output. Extreme fang length has apparently coevolved with extreme functions.

Variations of the cephalic muscles in the colubrid snake genera Entechinus, Opheodrys, and Symphimus

The cephalic muscles in three species of Entechinus, two species of Opheodrys, and Symphimus mayae display patterns of interspecific variation that are largely congruent with patterns of variation previously described for the skulls of these species. This congruence does not stem from direct correlation between the shapes of associated bones and muscles. In these colubrid snakes, most interspecific variations in muscle form involve changes in the shape or relative position of attachment points that appear unrelated to changes in the gross form of the bony surfaces forming the attachment points and produce no major changes in the architectural array of fibers in the muscle. Data presented here, combined with information from previous comparative studies of colubroid cephalic muscles, support the hypothesis that these muscles are limited in their potential variability by factors favoring parallel arrangements of fibers.