Free Owls Aren't Wise and Bats Aren't Blind by Warner Shedd Page A

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 southern 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 squirrel 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 reproductive 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 squirrel 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-fashioned 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 extremely 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 semihibernation of their cousins, southern flying squirrels are even more social than their northern counterparts when it comes to communal winter quarters. Twenty or more have been known to occupy the same winter home, and one observer reported that
fifty
southern flying squirrels shared a single tree cavity in Illinois!
    Although flying squirrels generally make little noise, they can vocalize, though the sounds are a bit different for each species. The northern flying squirrel emits low chirps and sometimes makes little clucking sounds when upset. The southern species, on the other hand, twitters, chirps, and utters high-pitched sounds sometimes described as “tseets.”
    As might be expected of small, largely defenseless creatures, flying squirrels of both species are a target for a wide variety of predators. Owls of various sorts are a major