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Saturday, April 12, 2008

Urban WIldlife Watch - Flying Squirrels

Photo credit: National Geographic and

How do Flying Squirrels Fly?

As the name would imply, flying squirrels are better suited for air travel. Scientists from Missouri studied these animals and found that their bodies, from their legs and hips, to the extra skin along the sides of their bodies, to their tails, reveal that these little squirrels are built for gliding across the sky.

Flying squirrels, Glaucomys sabrinus, are small rodents about half the size of the more familiar tree squirrel. Like the tree squirrel they live in trees, preferably older hardwood forest habitats of hickory and oak, because older trees provide the ideal habitat they require. They live in tree cavities and rotten snags and eat lichens and fungi on the forest floor.

They are called flying squirrels because they can leap from a tree branch, sail across the night sky, and land on another tree branch or the ground more than 100 feet away. The extra fold of skin that runs from their front legs to their back legs is called a gliding membrane. The squirrel uses the gliding membrane like a sail and its long tail like a boat rudder to maneuver across the night sky. So flying squirrels don’t actually fly, they glide.

The scientists wanted to learn how flying squirrels are able to glide such amazing distances in the air. The objective of the study was to learn more about how this animal moves both in the air and in the trees. Scientists examined the dynamics of gliding locomotion such as take off or launch, gliding, and landing components and looked at its walking behavior on tree branches. Launch speed, landing speed, and glide distance were measured for each squirrel in the study. Using frame-by-frame digital photography, the researchers were able to slow down the action and measure the angle of the jump and landing. They also measured launch and landing forces using specially designed launching and landing branches. To analyze flying squirrels walking behavior, they used wooden dowels that simulated tree branches of different diameters to see if squirrels responded differently when walking on larger or smaller branches. Using frame-by-frame digital video they were able to closely examine each squirrel’s walking behavior. The researchers measured speed, stride, how much weight each foot supported with each step, and the amount of time each foot is on the dowel when the animal is walking.

The team of researchers found that the aerial locomotion of flying squirrels is quite impressive. Squirrels can take off at speeds of nearly 10 yards per second, meaning they can glide very long distances. The farther a squirrel glides, the faster it glides. They actually take off at higher speeds if they are gliding longer distances. And they speed up faster as they approach landing in longer glides. Typically, squirrels land at a 45 degree angle, but the landing angle increases with distance. Moreover, the average observed landing force is about 2.9 times the subject’s body weight. This is true for both heavy squirrels, like pregnant females, and smaller squirrels like juveniles. A squirrel’s size has nothing to do with how well or fast it glides. Furthermore, when flying squirrels aren’t flying, they’re walking, on tree branches, that is. No matter the size of branch, large or small, they walk. As the squirrels travel along a branch, they maintain a steady, relatively slow pace.

Why do flying squirrels fly, or rather glide? The authors did not directly test this question but they think that gliding gives these squirrels a great advantage in patchy forests habitats. Firstly, gliding requires less energy than walking, which allows for travel from one place to another very quickly. Second, long distance gliding is a great way to escape a predator. If a flying squirrel spots a predator, it can distance itself from that predator very quickly. Finally, gliding reduces travel time between food patches. Squirrels are able to visit more food patches over greater distances. In complex habitats, like the ones flying squirrels live in, getting from one patch to the next and escaping predators as quickly as possible is always a plus.

As a confirmation, the scientists also examined the lower anatomy of flying squirrels. They examined the hip and thigh bones of flying squirrels. Based on size, shape, and position of these bones the scientists found that flying squirrels seemed to be better designed for leaping and less for walking along branches. They believe this is one reason why these squirrels are able to achieve such strong take offs and able to glide so far.
Scheibe, J., Paskins, K., Ferdous, S., & Birdsill, D. (2007). Kinematics and Functional Morphology of Leaping, Landing, and Branch Use in Glaucomys sabrinus Journal of Mammalogy, 88 (4), 850-861 DOI:


Miriam Goldstein said...

I want flying squirrels! For those of us who just can't get enough squirrel mechanics, would you mind posting a link to the research?

Anonymous said...

Here you go Miriam. I linked the article. it is an open access article from the Journal of Mammalogy.

Thanks for asking for it. Glad to know someone is so curious.

Anonymous said...

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