Of our mammals, a few of the rodents or gnawers, as the ground-hogs, gophers and chipmunks, hibernate in burrows deep enough to escape the cold, and either feed on a stored supply of food, or, like the snakes and crayfish, do not feed at all.

[Illustration:  CHIPMUNK.]

Others, as the rabbits, field-mice, and squirrels, are more or less active and forage freely on whatever they can find, eating many things which in summer they would spurn with scorn.  To this class belongs that intelligent but injurious animal the musquash or muskrat.  Those which inhabit the rivers and larger streams live in burrows dug deep beneath the banks, but those inhabiting sluggish streams and ponds usually construct a conical winter house about three feet in diameter and from two to three feet in height.  These houses are made of coarse grasses, rushes, branches of shrubs, and small pieces of driftwood, closely cemented together with stiff, clayey mud.  The top of the house usually projects two feet or more above the water, and when sun-dried is so strong as to easily sustain the weight of a man.  The walls are generally about six inches in thickness and are very difficult to pull to pieces.  Within is a single circular chamber with a shelf or floor of mud, sticks, leaves and grass, ingeniously supported on coarse sticks stuck endwise into the mud after the manner of piles.  In the centre of this floor is an opening, from which six or eight diverging paths lead to the open water without, so that the little artisan has many avenues of escape in case of danger.  These houses are often repaired and used for several winters in succession, but are vacated on the approach of spring.  During the summer the muskrat is, in the main, a herbivorous animal, but in winter necessity develops its carnivorous propensities and it feeds then mainly upon the mussels and crayfish which it can dig from the bottom of the pond or stream in which its house is built.

The bats pass the winter in caves, the attics of houses, and barns, or in hollow trees, hanging downward by their hind claws.  Motionless for months they thus remain, and those in the more exposed situations are, doubtless, frozen solid.  Yet, in time, their blood flows freely once again and they become as expert on the wing as though the year were one continual jubilee of insect chasing, and frost and snow were to them unknown.

All the carnivora, or flesh-eaters, as the mink, skunk, opossum, fox, and wolf, are in winter active and voracious, needing much food to supply the necessary animal heat of the body.  Hence they are then much more bold than in summer, and the hen yard or sheep pen of the farmer is too frequently called upon to supply this extra demand.

[Illustration:  A WOLF.]

But of all our animals it seems to me the birds have solved the winter problem best.  Possessing an enduring power of flight and a knowledge of a southern sunny sky, beneath which food is plentiful, they alone of all the living forms about us have little fear of the coming of the frost.  True, fifty or more species remain in each of the Northern States during the cold season, but they are hardy birds which feed mainly upon seeds, as the snow-bird and song sparrow; on flesh, as the hawks and crows; or on burrowing insects, as the nut-hatches and woodpeckers.