Nearly the entire life of a squirrel is spent in a death-defying, arboreal high-wire act where a miscalculated leap could spell disaster. To navigate their precarious daily rounds, squirrels make fast, sophisticated mental calculations to stick landings on wobbly branches and even deploy maneuvers frequently seen in the acrobatic free-running sport of parkour, reports Jonathan Lambert for Science News.
Those are some of the findings of a new study, published this week in the journal Science, that took a detailed look at the biomechanics and decision-making behind the gymnastic lifestyles of fox squirrels.
“As a model organism to understand the biological limits of balance and agility, I would argue that squirrels are second to none,” says study author Nathaniel Hunt, a biomechanics researcher at the University of Nebraska, in a statement. “If we try to understand how squirrels do this, then we may discover general principles of high performance locomotion in the canopy and other complex terrains that apply to the movements of other animals and robots.”
Researchers set up a series of experimental jumps in a eucalyptus grove at the University of California, Berkeley campus to make close observations of how wild squirrels approached different jumps, reports James Gorman for the New York Times.
One of the parameters the researchers tested was how the squirrels alter their jumps based on the bendiness of their launching pad and the distance they have to clear. If a branch was especially flimsy, the animals would initiate their jump earlier, even if the jump was relatively long. That’s because, according to Science News, the squirrels' choices of when to leap were influenced about six times more heavily by branch flexibility than they were distance.
“When they leap across a gap, they decide where to take off based on a tradeoff between branch flexibility and the size of the gap they must leap,” says Hunt in the statement. “And when they encounter a branch with novel mechanical properties, they learn to adjust their launching mechanics in just a few jumps. This behavioral flexibility that adapts to the mechanics and geometry of leaping and landing structures is important to accurately leaping across a gap to land on a small target.”
Despite all the variables researchers threw at their bushy-tailed study subjects, the squirrels never fell, per the Times. Even when things didn’t quite go as planned, the squirrels were able to just barely clasp the landing branch with their front paws and swing their bodies up and over onto their new perch.
When the team made the jumps more challenging by raising the height of the landing above the squirrel’s launch point and increasing the jump’s distance, the rodents went into parkour mode, twisting their bodies in mid-air and bounding off the adjacent wall. Sometimes the squirrel parkour was aimed at accelerating to cover more distance and other times it allowed the leaper to slow down to land on target. “It’s an additional point of control,” Robert Full, a biologist at the University of California, Berkeley and the paper’s senior author, tells Science News.
The researchers also observed that the squirrels quickly got better at navigating tricky jumps once they’d encountered them a few times, even if their first forays weren’t so graceful.
“Squirrels are used to making mistakes (the leaps are split-second decisions after all), but they succeed because they are experts at correcting themselves on the landing,” David Hu, a biomechanist at Georgia Tech who was not involved in the study, tells the Times via email.
“I think there is a moral in there for us all,” says Hu. “Don’t worry so much about a wrong leap, as long as you can recover like a squirrel, you’ll be fine.”