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Experiment confirms spikes on scaly tailed squirrel's tail let it perch on Iroko trees without slipping down

A team of bio-robotic specialists at the Max Planck Institute for Intelligent Systems has confirmed theories suggesting that scaly-tailed flying squirrels use their spiky tails to keep their perch in slippery trees. In their published in the Journal of the Royal Society Interface, the group generated 3D models of the squirrel tails and tested their friction on ramps with different grades of sandpaper.

Prior observations of scaly-tailed flying squirrels living in Ghana's Upper Guinean Forest, which is highly populated with Iroko trees—trees with smooth bark—have suggested their tails evolved to help them climb and perch on Irokos. But until now, such ideas have not been tested.

In addition to membranes between their front and hind legs that help them to remain aloft as they jump between trees, the squirrels also have two rows of pointed, raised scales along the underside of their tails. Their unique tails distinguish them from true flying squirrels. In addition to Ghana, the squirrels are also found in parts of Liberia.

To find out if the tails of the squirrels—which, as their name suggests, are scaly, not fluffy like those found in Europe and the Americas—assist in climbing the smooth-barked trees where they live, the researchers carried out an experiment. It consisted of generating 3D-printed models of the squirrel tails and then sliding them down ramps that were covered in different grades of sandpaper.

They found that the tails reached their maximum gripping ability when the sandpaper most resembled the bark of the Iroko tree, providing evidence that the tails are helpful in climbing and holding on to such trees.

The point of the work was to learn more about the climbing abilities of squirrels with different kinds of tails to use in building four-legged climbing robots. The results may prove useful in designing a tail for robots that can be used to help retain balance, as is the case with American and European squirrels, while also providing resistance against slipping down smooth barked trees.