With the arrival of April, we find ourselves back at the beginning of the annual cycle of the growing season. And what a wonderful time to be in our region. April is the month for the spring ephemeral flowers, taking advantage of the warmth of the soil, which is now at its’ peak, prior to the leaf foliation of next month. If there is anytime you can get out into the woods, this is the time to do it.
This is also the time of the year that our flying squirrels are nursing their young in tree cavities. By the end of the month, the mother may encourage the two or three young to make their first attempts at gliding. This April phenomenon involves the mother moving out on a limb with young in tow. After mastering hopping from branch to branch, the mother will call for them to make their first glide. Some are fearful and freeze, ‘churring’ for mother to come carry them back to the nest. Occasionally, a youngster will fall to the ground, requiring a trip back to the nest. In such situations, the mother will carry it by holding its stomach skin in her mouth, with the youngster wrapping it’s head and tail around its mother’s head.
Spring nests are normally tree cavities with 2” openings; just barely large enough to allow them entrance, but too small for larger predators (A rule of thumb is that the size of the opening will determine the resident). Often, a second brood will be had in August, although birthing does occur throughout the season. In either case, the pups will stay with their mother until the next brood is expected.
I’ve always tapped on trees with recent gnawing on cavity openings. To be truthful, I’ve not had a lot of luck, but from time to time, a flying squirrel with pop out to see what is happening. At that point, it’s not uncommon to see them glide from their nest tree to another tree. While bats are the only true flying mammals, flying squirrels will glide for distances up to 250 feet, depending on how high up in the tree they begin their flight. Basically, they glide three feet forward for every foot of drop. Their long and flat tail (80% of head and body length), enables 180° turning ability in flight.
It is often news to people that flying squirrels generally outnumber gray squirrels in our eastern deciduous forests. It’s just their nocturnal nature that makes them less apparent that the diurnal gray squirrels.
There are actually two species of flying squirrels in our Appalachian region; the northern (Glaucomys sabrinus) and southern flying squirrel (Glaycomys volans). In our region, the northern is now limited to several isolated populations on mountain top habitats of spruce forests. In 1985, the US FWS designated two subspecies populations as Endangered Species; one population centered in the Monongahela National Forest (Glaucomys sabrinus fuscus), and a second population center in the NC Appalachians, reaching as far north as the Mt. Rogers area of VA (Glaucomys sabrinus coloratus). At that time only 10 squirrels were captured in four separate areas of its WV subspecies range. Today federal and state biologists have captured more than 1,100 squirrels at over 100 sites. With the identity of such numbers and the maturation of forestlands in “the Mongo”, the FWS is in the process of delisting the G. s. fuscus subspecies at this time. Due to more limited habitat, the NC subspecies has not approached a level that would support delisting.
While the common southern flying squirrel and the rare northern species are almost identical in appearance (the southern has all white belly hairs; the northern has gray-based belly hairs), taxonomists are suggesting they come from different ancestries. While both came from Asia over the Bering Strait, the southern arrived in North America some 25 million years ago, with the northern only arriving roughly 12 mya. More revealing, it is the difference in the baculum (the penis bone found in most mammals) that supports this theory.
North American flying squirrels employ several nest types, and typically will use several nest types at a time. Shelters that are employed during night forays or as diurnal denning sites are called refugia nests. Shelters that are used to raise young are called natal nests. Shelters that are employed by a number of related or unrelated individuals during winter months are called aggregate nests. Flying squirrels are very gregarious, especially in winter, with up to 26 being found in an aggregate nest. They are also known to over winter in bluebird or other birdhouses. Summer leaf shelters, or dreys, are also commonly used, both for second broods (8-10” diameter shredded bark material) and refugia nests (much smaller).
The northern and southern flying squirrels are generally not sympatric (occurring in the same area; thus, they are allopatric); the smaller southern flying squirrel being more aggressive and tending to displace the larger northern flying squirrel. Where they overlap, populations of both are limited and unstable. Overlap areas generally support one species or the other. However, where there are good populations of the northern flying squirrel, red squirrel populations are almost always abundant. There is also evidence of a nematode parasite of the southern flying squirrel that is lethal or debilitating to the northern flying squirrel. When northern flying squirrels come down from their mountain habitats and come into contact with the southern flying squirrel, it would very likely pick up the parasite and perhaps suffer either sickness or at least a competitive disadvantage. On the other hand, when southern flying squirrel populations invade the spruce forest habitats of the northern flying squirrel, it cannot find adequate winter reserves of acorns to enable it to competitively survive the winters. Still, another factor comes into play regarding the nematode. The staminate spruce cones that make up a significant portion of the northern flying squirrel's spring diet are filled with highly aromatic oils that are known to have some potential as "vermifuges". It is possible that these cones provide the northern flying squirrel with some protection in the high elevation spruce forests, which is lost when it leaves the coniferous forests for the lower elevation oak forests. Interestingly, it has also been found that the success of the nematode is severely limited at colder temperatures.