Saturday, August 11, 2012

New Light on Rattlesnake Foraging Behavior

Crotalus ruber

Rattlesnakes rely on multiple sensory systems during foraging and like all pit vipers, rattlesnakes have a pair of heat sensitive, image-forming pits located on the front of their face. Thermal cues from these pits are integrated with visual cues in the central nervous system to produce a single image of the environment . The pits are particularly good at detecting warm images against cool backgrounds and therefore compensate for the reduced levels of ambient light at night. Aditionally, snakes rely on a chemosensory system that is not limited by the amount of light and they can obtain chemical cues in two ways: a nasal olfactory system that detects volatile chemicals; and a vomeronasal system which may obtain volatile and non-volatile chemical cues through tongue-flicking . The degree to which rattlesnakes rely on chemical and thermo-visual cues varies during the foraging process. Matt Barbour and Rulon Clark used radio telemetry and video surveillance cameras to quantify the sit-and-wait chemosensory foraging behavior of free-ranging red diamond (Crotalus ruber) and northern Pacific (Crotalus oreganus oreganus) rattlesnakes during day and night periods. The two most common behaviors they observed were chemosensory probes, a behavior they describe for the first time, and mouth gapes. During a chemosensory probe, the rattlesnake extends their head beyond their coil, explores the surrounding area while tongue-flicking, and subsequently return to a stationary position inside their coil. Foraging rattlesnakes probed at significantly higher rates at night than during the day. The snakes also mouth gaped at a higher percentage of nocturnal vs. diurnal hours for foraging snakes. Almost half of all mouth gapes were followed immediately with a chemosensory probe, suggesting that mouth gaping also serves a chemosensory function. Their results suggest that chemical cues play an increasingly important role in mediating rattlesnake foraging behavior at night. Examining how abiotic factors, such as light availability, influence the sensory ecology of free-ranging predators is essential for accurately characterizing their interactions with prey.
Barbour, M. A. and Clark, R. W. (2012), Diel Cycles in Chemosensory Behaviors of Free-Ranging Rattlesnakes Lying in Wait for Prey. Ethology, 118: 480–488.

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