Nature Bulletin No. 107 March 15, 1947
Forest Preserve District of Cook County
William N. Erickson, President
Roberts Mann, Supt. of Conservation
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
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
Why does sap rise in the trees? Why do birdies sing? Why do
boys play hooky.
it' s spring!
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Update: June 2012