EPOW - Ecology Picture of the Week

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Pit Viper Adaptations

Credit & Copyright: Dr. Bruce G. Marcot

Explanation:  How many adaptations to a predatory life style can you spot in these photos?   You are getting dangerously close to a juvenile western rattlesnake, photographed along the Middle Fork John Day River in eastern Oregon. Rattlesnakes belong the family Viperidae, or pit vipers, which is one hint... like other Viperids, rattlesnakes have infrared sensory pits below the nostrils, which help them detect body head of rodents and other warm-blooded (homoeothermic) prey.   The sensory pits complement three other senses also used in predation:  (1) eyesight, (2) smell (through the tongue and nostrils, using the Jacobson's chemoreceptory organs), and (3) sensing of vibrations through air or the ground.   Rattlesnakes are stealth or ambush predators.  They use the adaptation of cryptic coloration of their dorsum.  This includes the camouflage-like mottling that blends well into vegetation and soil.  It also includes the bold white lines on the head and back which may serve as disruptive coloration to visually break up the shape of the animal so prey won't recognize it as a snake and predator.  Note the heavily keeled dorsal scales.  Scales serve to reduce water loss, and the keels on the scales likely add structural strength and may scatter light and add to the animal's overall camouflage.  A characteristic of Viperids is that the head has small scales, but whether this is an adaptation per se is unknown.   Another adaptation is the vertical pupil of the eye, found in Viperids, lyre snakes, cat-snakes, and others.  Snakes with vertical pupils tend to be nocturnal or crepuscular, and when in daylight a vertical pupil can close more fully than can a round pupil. And of course, one major adaptation for quick locomotion through tight places and predatory efficiency is leglessness!

Next week's picture:  A Gondwana Island Forest