Squirrels use parkour tricks to leap from branch to branch

Squirrels navigate through trees by making rapid calculations. They have to balance trade-offs between branch flexibility and the distance between tree limbs.

Squirrels use parkour tricks to leap from branch to branch

For squirrels, advanced acrobatics are a matter of survival. When leaping between bendy branches that sway with the wind, the smallest error could spell death. New videos reveal how squirrels successfully leap from branch to branch.

These rodents make split-second calculations to plan jumps. Those decisions account for both branch stiffness and the distance between tree limbs. For super tricky jumps, squirrels improvise moves in midair. Researchers share these findings in the August 6 issue of Science. They find the squirrels’ tricks are similar to the stunts pulled by parkour athletes — people who scale walls, flip over railings and jump between buildings.

This is “a great example of how cool ‘normal’ animals can be,” says Michelle Graham. She wasn’t involved with the research. She does, however, study biomechanics at Virginia Tech in Blacksburg. “We’ve all seen squirrels do crazy stuff in nature,” Graham says. “But no one ever pays any attention to it.”

Unless, that is, you’re like Nathaniel Hunt. He has been awed by watching squirrels flash through trees for years. “Tree canopies are incredibly challenging environments to navigate,” says Hunt. He’s an integrative biologist at the University of Nebraska Omaha. To jump between bendy branches, a squirrel must judge how far it has to go and when to leap. Jumping from the base of a branch offers a sturdy foundation. But the squirrel may not be able to clear the length to the next branch. Moving toward the tip of the branch shrinks that distance. But that tip may be too flimsy to launch from. Hunt wondered, “How are they sensitive to that trade-off?”

To find out, he and his colleagues designed an artificial-forest obstacle course. Then, the team coaxed free-ranging fox squirrels (Sciurus niger) to run and jump through the course. The researchers rewarded their furry test subjects with peanuts.

First, the squirrels learned to leap from artificial branches across a gap. 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. High-speed video captured the jumps from launch to landing.  A total of 12 squirrels completed 96 leaping trials.

The squirrels leaped from bendier branches earlier. They may have been trying to maximize their jumping force. But that strategy also increased the distance that the animals had to clear.

To explore this behavior, the researchers ran computer models of squirrel jumps. One version of the model matched real squirrel behavior. And here, branch flexibility was six times more important than gap length for determining when a squirrel would jump. “We were surprised to see squirrels weighing both of these things … but in different amounts,” Hunt says.

To learn how squirrels leap between tree branches without falling, researchers trained free-roaming squirrels to complete an obstacle course. Camera footage shows that these rodents can learn to stick landings in just a few jumps. And squirrels consider both branch bendiness and distance before deciding to leap.

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 less than graceful. None fell, but most had clumsy landings. They grasped the landing peg with their front paws and swung around to pull themselves up. (Ideally, the squirrels would land neatly on all fours.) But squirrels got the hang of it within five tries, Hunt says. It just required adjusting their starting speed.

Such quick learning could come in handy if squirrels often cross the same tree limbs. That “might explain how they move so fluidly and rapidly” across particular branches, Hunt explains. “They’ve already learned what they need to know about that branch.”

The squirrels surprised the researchers in other ways too. For longer jumps — or those that required landing higher or lower than the starting point — squirrels got fancy. Many rotated midair and used their legs to “jump” off a nearby wall. This parkour-style maneuver helped them land difficult jumps. Squirrels also used parkour to slow down if they were coming in too hot to a landing. “It’s an additional point of control,” Hunt says.

For many tree-dwelling animals, “jumping between limbs is such a common thing,” Graham says. “Yet we so frequently only study it in pieces.” For instance, researchers might look at the launch but not the landing. This study gives a more complete view, she says. It’s “really interesting” that squirrels care more about branch stiffness than gap distance in planning jumps, she says. “I don’t know that I would’ve guessed that.”

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Tiny swimming robots may help clean up a microplastics mess

Big problem, tiny solution. Researchers in the Czech Republic have designed swimming robots that can help collect and break down microplastics.

Tiny swimming robots may help clean up a microplastics mess

To tackle a big environmental problem, chemists in the Czech Republic have been thinking small. Really small. Their new miniature robot has one purpose: To help clean up tiny bits of plastic polluting waterways across the globe.

Each new microrobot is no bigger than the tip of a sharpened pencil. They are magnetic and shaped like stars. When sunlight hits them, they produce chemical reactions that propel them through water in a specific direction. When they find a piece of plastic, they glom onto it and start to break it down. When the lights go out, they let go and are free to be used again.

In a new study, the scientists reported that these robots can either break down a piece of microplastic or hold onto it to be collected later.

“This work is great,” says Douglas Blackiston at Tufts University in Medford, Mass. He’s a biologist who did not work on the project but knows about such devices. He’s been designing robots out of living cells, including some that might help with pollution cleanup. Speaking of the new one, he notes that “these robots can eat plastic. They chew it up. Or they can retrieve it and be collected with a magnet. Scientists love robots with all these capabilities.”

Chemist Martin Pumera at the Czech University of Chemistry and Technology in Prague led the project. He studies ways to build microrobots. About a decade ago, he notes, scientists began developing tiny ‘bots that could move themselves in water. Then, they had to find them a mission. He says they thought: “Let’s make them do something useful.”

Pumera chose to focus on the problem posed by microplastics.

Polluting microplastics harm both animals and ecosystems

It’s a big problem. These are tiny bits of plastic, usually no wider than the top of a pencil eraser. And they’re everywhere — from the bottom of the ocean to air blowing onto ice atop mountains. They’ve turned up in drinking water, both bottled and tap water. Some studies estimate that trillions of pieces of plastic end up in the world’s waters. The plastic has many sources, from drinking straws and shopping bags to laundry and cleaning wipes. (Just think about how much plastic you encounter every day.) Plastic doesn’t easily degrade or fall apart. That’s always been one of its appeals.

“We have a big plastic pollution problem now,” says chemist Sherri “Sam“ Mason at Pennsylvania State University Behrend, in Erie. Using less plastic is the most important step, she says. After that, she says, comes cleanup. This is where she sees a role for Pumera’s robots. “I’m encouraged,” she says. They’re “a really interesting idea to help with cleanup efforts down the road.” Like Pumera, she notes that the robots aren’t yet ready to be widely deployed.

Pumera says his ultimate goal is to make cheap and environmentally-friendly robots that can be used anywhere in the world. He suspects that at first they might be most useful in plants that treat wastewater. There they can remove plastic before it reaches open water.

His group is not there yet. But in the June 2 ACS Applied Materials & Interfaces, they report getting close.

Making microplastics appetizing

Their design has two main ingredients. The first is bismuth vanadate. It undergoes chemical reactions and “swims” when exposed to sunlight. Pumera’s team uses chemical reactions driven by light to break down plastic. To do this, they coated the bismuth material with a magnetic film. That lets it collect the robots later — so pollutant-eating ‘bots will not just become more pollution.

In lab experiments, the star-shaped swimmers glommed onto each of four different types of plastic. And after a week exposed to light, the robots had reduced the weight of the plastics. It wasn’t much — only by percent. But that was an indication they were breaking the plastic down.

Meet the world’s smallest garbage collector. Sunlight striking this tiny robot starts chemical reactions that help it swim through water and break down tiny pieces of plastic. (The scale shows a span of 2.5 micrometers.)M. Pumera

They also caused the surface of the plastics to change from smooth to pitted. That’s another sign the robots were degrading it. Finally, the scientists showed that magnets could attract and retrieve the ‘bot troops at the end of the experiment — along with their plastic captives. Pumera says that they want to make the tiny garbage collectors reusable. They are also testing new robots that only swim at a certain depth; that would make them easier to recover.

The new study is a proof of concept type. That means it shows something can be done successfully, even if it’s only on a small scale.

In fact, Pumera says they still have a long way to go. There are many types of plastics. And even these microrobots are unlikely to succeed in degrading them all.

The researchers also have not yet shown how safe this system is for the environment, although Pumera says that’s their next goal. The first real-world test will be in a wastewater-treatment plant.

Indeed, says Blackiston, “They’ll need a lot of testing to show that they’re safe in open waterways,” such as at sea.

But he thinks that these challenges can be overcome. And one day, microrobots could play a big role in a worldwide cleanup effort. “The race is on among scientists,” he says. “We’re working on this problem from lots of different angles.”

This story is one in a series presenting news on technology and innovation, made possible with generous support from the Lemelson Foundation.

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