Animal behavior scientists strive to understand why and how animals do the things they do. Up until recently, scientists had to rely on natural observations -- fortuitous encounters or staged interactions. But advances in biorobots (mechanical robots that mimic live animals) are giving scientists unprecedented control over experimental variables, allowing them to run studies that would be unfeasible (or dangerous, or inhumane) in the course of normal research. They have already proved valuable for testing various animal communication hypotheses: flocking, mate selection, and animal communication. In this article, we examine new work by researchers from UC Davis and San Diego State University that pits a robotic squirrel, RoboSquirrel, against real-life rattlesnakes to study the subtleties of predator-prey interactions
Let me introduce you to RoboSquirrel:
RoboSquirrel is a robotic squirrel used to study predator-prey interactions between California ground squirrels and rattlesnakes. The work is still in its infancy (undergoing field trials), but here is an early video of RoboSquirrel interacting with a real-life rattlesnake:
In this set of screenshots, you can see one of the experiments (without tail-flagging), where a rattlesnake attacks the RoboSquirrel.
The RoboSquirrel was developed by a team of researchers from San Diego State University's Behavioral Ecology Lab led by Dr. Rulon Clark and by University of California Davis' Robotics Engineering Lab led by Dr. Sanjay Joshi.
Rattlesnakes and California ground squirrels have a long history as predator and prey, and each species has undergone intense co-evolution. We already know a lot about ground squirrel adaptations that prevent snake predation. Physiologically, ground squirrels evolved moderate resistance to rattlesnake venom. But they have also developed behaviors to thwart rattlesnake attacks. Instead of fleeing, they confront the rattlesnake, tail-flag vigorously (a behavior where they wave their tails back and forth), and sometimes fling dirt at the snake. When tail-flagging at rattlesnakes, squirrels heat up their tails -- presumably to make their tails more detectable to rattlesnakes which have heat-sensing pits on their face. We saw this behavior in the RoboSquirrel video, and you can see it in the video below with a real squirrel (or in these supplementary videos, one and two):
Although we know a lot about squirrel adaptations, we lack an understanding of how snakes respond to squirrel harassment (specifically the tail-flagging signal) and the behaviors they have evolved to become successful predators. Natural observations have helped very little, as snakes rarely make overt reactions when squirrels approach. Enter RoboSquirrel.
Dr. Clark and Dr. Joshi worked together to develop a life-like robot, RoboSquirrel, that can be presented to free-ranging snakes. RoboSquirrel is made from a taxidermic skin and is kept in captive squirrel bedding to make it smell realistic. The body and tail are heated by copper coils to give it a realistic thermal signature. The tail temperature can be increased above body temperature during predator-prey interactions, just as performed by real ground squirrels. The robot is equipped with a servo motor that produces programmable tail-flags.
Dr. Clark’s team is currently using RoboSquirrel to understand tail-flagging behaviors. The basic hypothesis: Tail-flagging discourages the snake from striking during squirrel-snake interactions. Using RoboSquirrel, researchers present a “squirrel” to a hunting snake with and without the tail-flagging signal (something live squirrels would never do willingly) to see if it results in an appreciable difference in the number of snake strikes. Similarly, the heat signature of the tail can be varied to observe the resulting snake behavior. Field studies are still ongoing, so we will not know the outcome of his experiment for a while yet. However, preliminary work has shown that snakes perceive the robot as realistic, sometimes making predatory strikes (see video).
Thanks to RoboSquirrel, this research will give us a more complete view of predator-prey relationships and co-evolutionary processes.
The RoboSquirrel is just one BioRobot example. Robotic models have been made for diverse organisms, including: electro-mechanical honeybees, robot fish, robot lizards, robot birds, and robot fiddler crab claws. Clearly, robots are becoming an increasingly-valuable tool for animal behavior researchers.
About the Author:
Bree Putman is an Ecology Ph.D. student at San Diego State University and UC Davis. She studies rattlesnake-small mammal interactions and rattlesnake foraging behavior. She has a deep respect for snakes and immensely enjoys peering into their secretive lives. When she is not stalking snakes, she likes crocheting, cooking, and watching reality TV shows. Visit her blog here.