It was only about two months ago when I took inventory of all my wood duck nest boxes. It's always interesting to me to learn what species of wildlife was, or is, occupying each of the houses. This year's box-check revealed successfully hatched wood ducks and hooded mergansers, as well as abandoned nests full of unhatched wood duck eggs. There was also the usual array of gray squirrel nests and one or two vacant boxes that still had the layer of wood shavings I had left inside the year before.
One particular box that overlooks the lake and is nailed to an old and declining jack pine tree caught my eye as I approached the structure from underneath. The wood of the rear corner of the box's bottom was heavily stained, obviously soaked from a liquid of some kind. I thought it was unusual to observe such staining on the bottom of the nest box and not on top, as one might expect from the elements. But I had a hunch.
Hoisting myself up into the old pine's branches, I slowly climbed up to the box to have a peak inside. As I began to open the side door of the nest box, I heard shuffling noises from somewhere inside the duck house. Sure enough, when I pried the door open, I could see the telltale nesting material that is used by a very special little rodent. The nest, consisting of mostly mosses and arboreal lichens, is the stuff of choice for northern flying squirrels.
A few seconds later out popped the bug-eyed nocturnal squirrels into the bright blue daylight of the late March day. They didn't seem overly bothered by my intrusion, but, nonetheless, the handsome fellows scampered out the entrance hole and shimmied up the tree to evidently watch what I was up to.
One thing about a flying squirrel nest that isn't very becoming, is that it typically reeks of urine. Their bedside manner leaves something to be desired. Yet, as is the case with flying squirrels, such urinary behavior has more to do with marking one's territory. And it was also why the bottom of the nest box was so visibly soiled.
Two species of flying squirrels inhabit Minnesota: one, as already mentioned, is the northern flying squirrel (Glaucomys sabrinus). The other species is the southern flying squirrel (Glaucomys volans). Both mammals are rodents and are members of the squirrel family, Sciuridae. It is the northern flying squirrel that populates our forests here in the Northland.
Northern flying squirrels have the most extensive distribution in Minnesota and North America. They occur throughout central and northern Minnesota in a variety of forest types. The North American range of southern flying squirrels is mostly east of the Mississippi River, which includes central and southeastern Minnesota. Both species prefer habitats of mature, broad-leaved forests.
Northern flying squirrels are larger than their southern relatives -- about 12 inches versus 9 inches long. Both species are about the size of chipmunks. The color of their fur coats is similar for both squirrels, ranging from brownish to brownish gray. Belly fur is whitish.
The tails of flying squirrels, a distinguishing feature, are long, flat and fluffy. Such tails act as rudders as they glide through the air. Their eyes are very large and ringed with black fur. But the flying squirrels' most distinguishing feature is the folds of skin between their legs. This furred membrane, called a patagium, stretches between the front and back limbs and is attached to the ankles and wrists.
Flying squirrels are especially active at night, but can also be observed at dusk and dawn. They feed on a variety of seeds, grains, fruits, berries, buds and nuts. Their diet also includes fungi, mushrooms, insects, bird eggs and even young birds and carrion. The inquisitive and docile-acting squirrels are common nighttime visitors to backyard birdfeeders. Most people don't mind watching bands of flying squirrels raiding their feeders in the dark of night.
Contrary to some beliefs, flying squirrels really don't fly -- they glide. The whole sequence, from launch to landing, is really nothing more than a controlled freefall. By launching themselves from the upper parts of trees and other structures, flying squirrels glide through the air to reach the lower parts of nearby targets.
This amazing descent is accomplished by extending their limbs to expose the patagium stretched between their feet and by holding their tails straight behind them. Flying squirrels are capable of maneuvering and steering their bodies in order to land where they want to. Resembling Aladdin's flying magic carpet, a flying squirrel's glide can extend 100 feet or more.
Nests are usually constructed inside naturally occurring tree cavities and woodpecker holes. But, as I've learned over the years, artificial nest boxes, including bluebird houses, are favorite nest sites too. During the winter, several flying squirrels will often den together to stay warm. Litters of up to seven, but usually two-four, pups or kits are born blind and hairless in the spring.
Indeed, if you feed birds and are fortunate to live where flying squirrels inhabit, which is probably the case whether you know it or not, watch your birdfeeders at night. If you discover that flying squirrels are present, try arranging outdoor lighting directed at your feeders in order to better observe these curious species of squirrels. Believe me, it's a fine way to pass the time as you get out and enjoy the great outdoors.
Blane Klemek is the Bemidji area assistant wildlife manager, DNR Division of Fish & Wildlife. He can be reached at email@example.com