Biology Reference
In-Depth Information
carnivorous of all the tree squirrels. Nestlings and birds' eggs, carrion, baby mice and voles, and even
adult mice and shrews are killed and consumed by this little terror. Moreover, as it turns out, the south-
ern flying squirrel is considerably more aggressive than its much larger northern cousin and generally
is dominant wherever the two species inhabit the same tract of forest.
There are other differences between the two species, as well. For example, the northern flying squir-
rel molts twice a year, shedding its fur in May or June, and donning a heavier winter coat in September.
The tail, however, only molts once, in early summer. The southern flying squirrel, on the other hand,
molts only once, in September.
There are also differences in reproduction and nesting habits. Northern flying squirrels usually have
only one litter a year—an eminently sensible system, considering the all-too-brief summer throughout
much of this squirrel's range. They breed in late winter and, after a forty-day gestation period, give
birth to between two and five blind, naked young.
In contrast, southern flying squirrels usually have two litters a year throughout much of their
range—one in the period from February to May, the second from July to September. The dual litters
reflect the much longer warm season available to the southern flying squirrel, which takes full repro-
ductive advantage of this climatic benefit. After a forty-day gestation, they give birth to tiny, naked,
blind young, each weighing less than one-quarter ounce.
As in the majority of mammals, male flying squirrels of both species do nothing to help raise their
offspring. The females, however, are excellent mothers that defend their young and are known to move
them to a new nest if parasites become too abundant in the original nest.
Living quarters and winter habits for the two species also vary. In summer, the northern flying squir-
rel builds summer nests, usually close to the trunk of an evergreen tree. In winter, however, they reside
in tree cavities, often enlarged from the prior labors of woodpeckers.
In far northern climes, these squirrels often hollow out growths known as witches' brooms. These
peculiar masses are caused by a fungus that sometimes infects spruce and balsam fir trees. The fungus
causes the tree to grow a dense, tangled maze of tiny branches that somewhat resembles an old-fash-
ioned broom—hence the name. This hollow in a witch's broom, after being heavily lined with grass,
feathers, or other soft material by the enterprising occupant, is evidently warmer than a tree cavity lined
with soft material.
Flying squirrels of both species are quite sociable in winter, and as many as eight northern flying
squirrels of the same sex may share winter quarters, providing warmth for each other in the den. In ex-
tremely cold weather, northern flying squirrels semihibernate, often sleeping through several days until
the weather moderates.
Southern flying squirrels also build summer nests, although these are leaf nests in hardwood trees
such as oaks and hickories. Although they remain active all winter, and eschew the occasional semi-
hibernation of their cousins, southern flying squirrels are even more social than their northern coun-
terparts when it comes to communal winter quarters. Twenty or more have been known to occupy the
