For squirrels, advanced stunts are a matter of survival. When jumping between flexible branches that sway in the wind, the smallest mistake it could mean death. New videos reveal how chipmunks successfully jump from branch to branch.
These rodents do split-second calculations to plan their jumps. These decisions explain both the stiffness of the branches and the distance between the branches of the trees. For super hard jumps, squirrels improvise mid-air moves. The researchers share these findings in the issue of August 6 of Science. They find that squirrel tricks are similar to stunts of parkour athletes: people climbing walls, overturning railings and jumping between buildings.
This is “a great example of how awesome even the simplest animals can be,” says Michelle Graham. She wasn’t involved in the research. However, he studies biomechanics at Virginia Tech in Blacksburg. “We’ve all seen squirrels do crazy things in nature,” says Graham. “But no one has ever paid attention to it.”
Unless you’re like Nathaniel Hunt. He was stunned looking at the squirrels snap shots through the trees For years. “The crowns of trees are incredibly difficult environments to explore”says Hunt. He is an integrative biologist at the University of Nebraska Omaha. To jump between flexible branches, a squirrel has to judge how far it should go and when to jump.
Jumping off the base of a branch offers a solid foundation. But the squirrel may not be able to get past the length of the next branch. Moving towards the tip of the branch reduces that distance. But that point may be too fragile to start over. Hunt wondered: “How are they sensitive to this compromise?”
Squirrels to the test
To find out, he and his colleagues designed an obstacle course in an artificial forest. Then, the team convinced the Sciurus niger squirrels to run and jump across the path. The researchers rewarded their furry subjects with peanuts.
First, squirrels learned to jump from artificial branches through empty space. Some branches were stiffer than others. On the other side of the gap was a prize: a basket of peanuts attached to a landing peg. The high-speed video captured the jumps from launch to landing. A total of 12 squirrels completed 96 jumping trials.
Squirrels jumped off the more lithe branches first. They may have been trying to maximize their jumping strength. But that strategy also increased the distance the animals had to cross.
To explore this behavior, the researchers have run computer models of squirrel jumps. One version of the model matched the behavior of the real squirrel. And here, branch flexibility was six times more important than gap length in determining when a squirrel would jump. “We were surprised to see squirrels weighing both of these things … but in different quantities”says Hunt.
The researchers took their obstacle course to the next level for five squirrels. Here the branches were more flexible and the gap between them widened. The squirrels’ first leaps were anything but graceful. Nobody fell, but most had awkward landings. They grabbed the landing peg with their front legs and turned to pull themselves up. (Ideally, the squirrels would land neatly on all fours.) But the squirrels figured this out in five tries, says Hunt. It only required adjusting their starting speed.
Such quick learning could come in handy if squirrels often traversed the same tree branches. This “Could explain how they move so smoothly and quickly” through particular branches, explains Hunt. “They have already learned what they need to know about that branch.”
The squirrels surprised the researchers in other ways as well. For longer jumps, or those that required a landing higher or lower than the starting point, the squirrels had fun. Many rotated in mid-air and used their legs to “jump” from a nearby wall. This maneuver parkour style helped them make difficult jumps. Squirrels also used parkour to slow down if they were coming too heavy in the landing. “It’s another point of control”says Hunt.
For many animals that live in trees, “Jumping between branches is such a common thing”says Graham. “Yet we study it so often only in pieces.” For example, researchers could look at launch but not landing. This study provides a more comprehensive view, he says. AND “really interesting” let the squirrels worry more of the stiffness of the branches than of the distance between the jumps in their planning, he says. “I don’t know if I would have imagined it.”