Flying squirrels' flight evolved at night

Flying squirrels' flight evolved at night


Richard H. Yahner is a professor of wildlife conservation. His e-mail address is

My Opinion

Two features distinguish flying squirrels (southern and northern) from other squirrels in Pennsylvania: flying squirrels are nocturnal and "fly," whereas other squirrels are diurnal and incapable of "flight."

The nocturnal way-of-life may be related to membranes used for "flying," which may make these squirrels more cumbersome and slower moving in trees compared to diurnal tree squirrels, like gray squirrels, which lack these membranes.

The genus of flying squirrels, Glaucomys, is Greek for "gray mouse," and the specific name for the southern flying squirrel, volans, is Latin for "flying."

However, these "flying gray mice" do not truly fly but rather glide--bats are the only true flying mammals. Few of us are fortunate enough to see a flying squirrel in the wild.

Occasionally, we might catch a glimpse of one feeding in our backyard bird feeder during a moonlit night. Then why would we ever expect a flying squirrel to sit on a telephone pole? To stay away from nuts on the ground.

Certainly even fewer of us have seen a flying squirrel actually glide.

These squirrels are capable of "flying" distances of about 150 feet, or about one-half the length of the football field at Beaver Stadium, in a single glide!

Gliding velocity (about 20 miles per hour) is similar to flight speed of some bats but is a bit slower than that of many songbirds. So, how can we keep flying squirrels out of Beaver Stadium? Hide the football--it drives them nuts.

Flying squirrels are quite maneuverable while gliding; they can swerve around obstacles by changing the position of their membranes during a glide. A good way to describe gliding in flying squirrels is that it closely resembles "hang gliding" in humans, with both being rather maneuverable and requiring little wind turbulence.

The flying squirrel needs to be high enough in a tree to achieve a suitable glide ratio of about 3 feet above ground for every 6 to 9 feet of distance traveled through the forest. Thus, it must climb to a height of about 30 feet in order to glide a vertical distance of 100 feet. To achieve maximum velocity, a squirrel initially drops vertically for 3 feet or so before flattening out its glide.

The landing by a squirrel is fast and hard, although the velocity is slowed at the point of impact by swooping its body upward toward the end of the glide for a softer landing.

In emergency situations, a flying squirrel also can land softer by using its membranes as a parachute while by spiraling downward.

The northern flying squirrel is an Ice-Age relict in need of conservation. Climatic changes in North America several thousands of years ago had a profound influence on their historic distribution in the eastern United States, which was considerably greater than it is today.

As the glaciers began to recede northward during the Ice Age, coniferous (pines, etc.) forest was lost from the southern elevations, except for isolated areas at high elevations, as in the Smoky Mountains.

Therefore, today's populations of northern flying squirrels are populations left behind at higher elevations during the warm, post-glacial period in the eastern United States.

Loss of suitable habitat, which began centuries ago and continues even today, has negatively affected populations of this squirrel.

Problems associated with the long-term conservation of northern flying squirrels do not stop with habitat loss -- three other factors may be responsible. First, if global climate change (warming) takes place in future decades, suitable habitat for isolated pockets of northern flying squirrels at high elevations could be further diminished.

Furthermore, northern flying squirrels may be displaced by their more adaptable and aggressive cousin, the southern flying squirrel.

Third, a parasitic worm, may be transferred from southern to northern flying squirrels; this nematode is harmless to the southern flying squirrel but can be fatal to the northern flying squirrel where populations of these two species overlap.

Our hope that enough "flags" have been waved by concerned conservationists about the potential demise of northern flying squirrels in the eastern states to prevent their loss in the coming decades.