AMHERST - One gray squirrel, its bushy tail twitching, barked a warning as another scrounged for food nearby.
It was an ordinary spring day at Hampshire College, except that the rodent issuing the warning was powered by amps, not acorns.
Dubbed "Rocky" after the cartoon character, the robosquirrel is working its way into Hampshire's live-squirrel clique, controlled by researchers several yards away with a laptop computer and binoculars.
Sarah Partan, an assistant professor in animal behavior at Hampshire, hopes that by capturing a close-up view of squirrels in nature, Rocky will help her team decode squirrel communication techniques, social cues, and survival instincts.
Rocky is among many robotic critters worldwide helping researchers observe animals in their natural environments rather than in labs. The research could let scientists better understand how animals work in groups, court, intimidate rivals, and warn allies of danger.
In Indiana, for example, a fake lizard shows off its machismo as researchers assess which actions intimidate and which attract real lizards. Pheromone-soaked cockroach counterfeits in Brussels, meanwhile, exert peer pressure on real roaches to move out of protective darkness. In California, a tiny video camera inside a fake female sage grouse records close-up details as it's wooed by the breed's unusually promiscuous males.
The research may even help explain similar instinctive behaviors in humans, researchers say.
"Animals and humans are all affected by behaviors, body postures, and signals from each other that we may not be aware of," Partan said.
The use of fake critters to infiltrate real groups of animals is so new that few companies build or sell such tools to researchers.
Many of the scientists using animal doppelgangers have modified toy animals or, like Partan and her students, cobbled together their own with fake fur, small motors, circuits, and other material. Partan, who created Rocky a few years ago with students when she taught at the University of South Florida, is constantly refining its actions and updating its technology.
Rocky's movement is controlled by basic computer programs, and it has tiny speakers inside that play recordings Partan purchased from an animal-sounds library at Cornell University.
One recent afternoon, she and students Maya Gounard, 20, and Andrew Fulmer, 19, brought Rocky out for field testing and placed him near real squirrels. Mounted on a board, he was shielded by a camouflage hood, and a long cord connected him to the researchers' laptop.
After the computer's program flipped the hood open, Rocky went into a sequence of tail-flagging, barking, and other motions squirrels recognize as warnings.
The most successful experiments are when the real squirrels respond by "flagging" their own tail, halting their foraging to check for danger, scamper up a tree, or take other actions that show they picked up on the signals, Partan said.
"We watch for a trade-off in their behavior," she said, pointing out a squirrel that jerked to its hind legs and froze, its eyes scanning the area as it heard Rocky's barks. "He gave up foraging to focus on being vigilant, so that's something we'd note as a discernible response."
They focus on whether squirrels react more strongly to Rocky's noises or movements or a combination that researchers call multimodal signals.
"Whether it's a bunch of squirrels in a field or humans in a mall, there are general principles of behavior that seem to hold up across species lines," said Greg Demas, director of Indiana University's Center for the Integrative Study of Animal Behavior.