Nature Bulletin No. 107   March 15, 1947
Forest Preserve District of Cook County
William N. Erickson, President
Roberts Mann, Supt. of Conservation

****:SPRING AWAKENING

The hibernating animals are awakening from their long winter 
sleep. Reptiles, amphibians, land snails, numerous insects, and 
some of the mammals pass the long northern winter months in a 
strange torpid condition known as hibernation.

Some snakes may be found tightly coiled beneath logs or piles of 
rocks; others in burrows and caves. Frogs and most turtles bury 
themselves in the mud and vegetation at the bottom of a pond or 
stream, emerging when the ice breaks up in early spring. Toads 
bury themselves in the ground, digging their way backward with 
their horny heels. Some butterflies migrate; others pass the 
winter in hollow logs or in buildings, emerging to fly about on 
the first warm spring days. Some mosquitoes hibernate. Most 
insects, however, go through winter in the egg, larva, or pupa 
stage.

Few mammals migrate seasonally. Some species of bats do but 
others hibernate in caves. Rabbits, squirrels, foxes, muskrats, 
mink, weasels, field mice and deer mice are present and active 
all winter. The bears, skunks, raccoons, possums and chipmunks 
store up thick layers of fat and go to sleep in their dens when the 
severe cold comes. But they are light sleepers and on mild 
winter days are likely to awaken, come out, and move about.

Other mammals, however, truly hibernate. The woodchuck or 
groundhog, the gopher, the 13-striped ground squirrel, the long-
tailed jumping mouse, and some of the bats, eat and eat until a 
third or more of the animal's weight is fat, and then retreat to an 
underground chamber where they enter a death-like sleep which 
may last from October until late March. All but the bats curl up 
in a tight ball. Breathing is faint, at long intervals. Heart beat is 
slow, circulation sluggish: if the toe of a mouse or a bat is cut 
off during hibernation, very little bleeding occurs. Body 
temperature drops to near that of the surroundings, sometimes 
close to freezing. Most of the stored fat is slowly used up. No 
one known just what awakens them. Temperature changes 
perhaps.

Why does sap rise in the trees? Why do birdies sing? Why do 
boys play hooky?

Because it' s spring!