Olympic gymnasts amaze the world with their performance on the uneven bars. Fortunately, they don’t have to compete with squirrels.
Suppose instead of the uneven bars, human gymnasts had to fly through the canopies of trees, jumping gaps of different distances, from branches of different thicknesses, some stiff, some resilient. And every landing would be different, on everything from trunks to twigs.
Oh, and then there are the hawks to watch out for.
What makes squirrels so good?
Cognitive scientists and biomechanics experts at the University of California, Berkeley, wanted to test both the agility and decision-making of wild fox squirrels in a eucalyptus forest on the edge of campus. This is a different species from the common eastern gray squirrel, but both are experts at navigating treetops.
Not only did the researchers record the squirrels’ jumping and landing, they were also able to analyze the decisions the animals made about how and where to jump. In part of the experiment, the animals invented parkour-like moves halfway through the jump to bounce off a vertical wall and adjust their speed and distance, disrupting the original purpose of the test.
Lucia F. Jacobs, a cognitive psychologist who has studied squirrels extensively and was one of the authors of a report on the work in the journal Science, said, “In some ways, as a squirrel biologist, this is not very surprising. If we consider a squirrel-Olympic Games, this wouldn’t even be the qualifier.”
But the meeting of cognitive and biomechanical minds to conduct a joint investigation was unusual.
Nathaniel H. Hunt, the lead author of the paper, started the project when he was a graduate student, leading the actual squirrel events with Judy Jinn, a student in Dr. Jacobs and a co-author.
dr. Hunt, now at the University of Nebraska, Omaha, said many previous biomechanics studies focused purely on the structure and movement of animals, but this group wanted to understand decision-making, learning and creativity in the context of physical challenges.
He said squirrels were a good choice because not only are they athletic, but they also have a great ability to make decisions, solve puzzles and learn.”
dr. Robert J. Full, a biomechanics expert and another author, said the first question was how the squirrel weighed the variables of a branch’s distance and flexibility when setting up a jump. Getting to the end of a branch, where one twig is very pliable, can provide a very short jump to the next branch. But bendable branches don’t provide a solid jumping platform, so you can’t count on using your muscles efficiently.
The squirrels (all wild, all free to come and go), were trained to jump along perches to get a reward of peanuts. The team made several perches, or artificial branches, that looked the same on the outside but had different resilience along the length of the branch and between the branches.
The researchers found that the stiffness of the launch branch was the most important thing for the squirrels. “They care more about a stable starting position, about six times more, than about how far to jump,” said Dr. full.
The squirrels also learned quickly when a stiff branch was replaced by a similarly resilient branch. And they never fell during the trials, mostly because they made aerobatic landings: underswing, overswinging, hanging from their front limbs. All maneuvers familiar to anyone who has ever tried to set up squirrel-proof bird feeders.
The researchers also changed the length of the jumps and the height of the launches to see if exercise and learning would increase the general competence of some squirrels. But the squirrels just changed the way they jumped. “They decide to park off the wall and land on the perch,” said Dr. full. They adjusted their jump in the middle, increasing or decreasing their speed.
The subjects of the experiment were absolutely unimpressed with the new challenge, said Dr. full. “They kind of look at us like, ‘We’re squirrels…'”
David Hu, who studies animal movements at Georgia Tech, said he found the inventiveness of the parkour movement interesting. “There should be more of this kind of work — looking at the creativity of animals when dealing with tasks that are impossible without innovation.”
He also liked the way the squirrels handled mistakes. They are not perfect at all and often overshoot or under their target. But they still have the ability to land.
“Squirrels are used to making mistakes (the jumps are split-second decisions, after all),” he said in an email, “but they succeed because they are experts at correcting themselves on landing.”
“I think there’s a moral in it for all of us,” added Dr. Hu to it. “Don’t worry about a wrong jump, as long as you can recover like a squirrel, you’ll be fine.”