A rodent scuttles innocently through the desert in New Mexico, minding its own business and then bang! A resting but ready pit viper lashes out in a lightning quick attempt to snatch up some dinner. These predator-prey interactions play out countless times every day and are over in an instant, but armed with cutting-edge video technologies, biologists are now able to observe them in mesmerizing new ways.
Vipers are generally thought to be have the fastest strike among their serpent friends, though research last year found that other non-venomous snakes can lunge with similar acceleration – more than 270 m/s squared (about 886 ft/s squared), or around 0 to 100 km/h in just 0.10 seconds. In studies like this one, scientists will observe the snake strikes in controlled laboratory settings with high-speed cameras, but technological advances have now made it possible to take these devices out into the animal's natural environment, where its a whole different ball game.
"Predator-prey interactions are naturally variable – much more so than we would ever observe in a controlled laboratory setting," says Timothy Higham, an associate professor of biology at University of California, Riverside. "Technology is now allowing us to understand what defines successful capture and evasion under natural conditions. It is under these conditions in which the predator and prey evolve. It's therefore absolutely critical to observe animals in their natural habitat before making too many conclusions from laboratory studies alone."
So Higham and his team ventured out into the New Mexico desert with infrared-sensitive video cameras and used them to film radio-tracked Mohave rattlesnakes, highly venomous pit vipers, striking at Merriam's kangaroo rats. Captured in high-speed video of 500 fps, the researchers found viper strikes in natural habitats to be highly variable.
The strikes occurred at distances ranging from 4.6 cm to 20.6 cm (1.8 in to 8.1 in). The maximum acceleration observed far exceeded those seen in lab settings, at more than 500 meters per second squared. Success was also varied, with the team recording four hits and four misses, with two deemed the result of the snake's inaccuracy and two due to the rats artful escape maneuvers, which Higham says might be due to elastic energy storage.
"Elastic energy storage is when the muscle stretches a tendon and then relaxes, allowing the tendon to recoil like an elastic band being released from the stretched position," he explains. "It's equivalent to a sling shot – you can pull the sling shot slowly and it can be released very quickly. The kangaroo rat is likely using the tendons in its lower leg – similar to our Achilles tendon – to store energy and release it quickly, allowing it to jump quickly and evade the strike."
The team now plans to apply this approach to other species of rattlesnake to explore how they handle these predator-prey interactions.