Rattlesnake Foraging Behavior

 

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This clip illustrates the basic ambush site selection behavior of a pitviper, in this case, the nocturnal movement of a timber rattlesnake (Crotalus horridus) from one ambush site to another. Note how slowly and carefully the snake glides across the forest floor, tongue-flicking along the way. It eventually investigates a large fallen log and decides to set up an ambush location along side it. This snake waited at that ambush site for over 48 hours before giving up and moving to a different location.




















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Even during the day a snake coiled in ambush on the forest floor can be difficult to see. This clip shows a timber rattlesnake (Crotalus horridus) in a typical ambush posture:  tight coil, head and neck cocked back in a ready-to-strike position, oriented perpendicular to fallen log with tip of snout resting on log. The yellow coloration of the snake helps it blend with the dappled light and fallen leaves on the forest floor. Incidentally, this is “Hank”, the same snake that we followed with the BBC crew when filming the timber rattlesnake predatory behavior sequence for David Attenborough’s “Life In Cold Blood”.



 


















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Occasionally we record somewhat unusual foraging behaviors. Most pitvipers envenomate mammals by striking, injecting venom, and then immediately releasing the prey. The prey then runs a short distance before being immobilized and killed by the venom, after which the snake follows the scent trail left by the fleeing animal in order to find and swallow it. However, in this case, a red-diamond rattlesnake (Crotalus ruber) held on to this mouse after injecting venom, and continued to hold the animal until it was immobile. The snake then swallows the mouse and remains in place at this ambush site. Note that this whole process takes about 30 minutes, but the video is sped up after the first 30 seconds so that we can show the entire process in a short clip.



















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One of the more surprising patterns to emerge from our fieldwork is the frequency with which snakes missed their strikes. Over half of the strike attempts are misses. The biggest factor affecting the success of a strike is the ability of prey animals to initiate an evasive “dodge” maneuver in the fraction of second after the snake initiates a strike, but before the head of the snake reaches it. Here’s an example of a small ground squirrel pup dodging out of the way of a strike from a northern Pacific rattlesnake (Crotalus oreganus). The snake is striking while hidden in the vegetation to the upper right from the squirrel. After the real time view, the strike is also shown in slow motion. In the slow motion view, you can see the erected fangs of the snake as its head moves out of the brush and toward the squirrel. The snake makes a biting motion at the end of the extension stage, bearing down on the spot occupied by the squirrel in the previous video frame.



















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This clip also shows a squirrel that is able to successfully dodge a rattlesnake strike (with the strike shown in slow motion after the real time sequence plays through). In this case, the forward motion of the strike unbalances the snake and causes it to fall down the slope. This sequence illustrates one of the reasons snakes may attempt to time their strikes carefully; a missed strike results in a loss of crypsis (they become obvious to their prey and predators), and in same cases can leave them in a very vulnerable position.