When the food of the grizzly bear becomes scarce, he goes to bed and
sleeps until a reasonable supply is available, even though he waits five
months for it. He feasts on the fullness of the land during the summer
and wraps himself in a thick blanket of fat. When winter comes on, he
digs a hole and crawls in. This layer of fat is a non-conductor of cold
and in due time is drawn on for food.
One autumn day I visited the Hallett Glacier with a professor from the
University of Chicago. After exploring one of the upper crevasses, we
stood looking down the steep slope of the glacier. New snow had fallen a
few days before, and a soft, slushy coating still overlaid the ice. The
professor challenged me to coast down the steep, snow-lubricated
ice-slope. We seated ourselves on this soft, slippery snow, and he gave
the word "Go." Just as we slid away, we saw at the bottom of the slope,
where we were soon to be, a huge grizzly bear. I wish you might have
seen our efforts as we tried to change our minds on that steep slope!
The grizzly was busily eating grasshoppers, but he heard us coming and
fled at a racing gallop, giving an excellent exhibition of his clumsy
hind legs reaching out flat-footed.
Each autumn numbers of insects and sometimes bushels of grasshoppers
either are blown upon the ice and snow or else approach it too closely
and fall from having their wings chilled. Evidently the grizzlies long
ago learned of this food-supply, for the ice-fields are regularly
visited by them during the autumn. Along the timber-line the grizzly
feeds freely upon the last of autumn's berries and the last green
plants. Many a grizzly goes to the heights to put on fat for his long
winter's sleep.
Bear food becomes scarce as winter approaches. Fruit, berries, grass,
and weeds are out of season; most birds and insects are gone. The bear
feeds on what remains--small animals which he digs out, a stray stranded
fish, now and then a dead bird or animal carcass, the red fruit of the
rose, and the nuts, bark, and roots of trees and plants. I do not
believe the grizzly eats a special or a purgative food during the few
days preceding his denning up, although he may do so.
On the few occasions when I have been able to keep track of a bear
during the four or five days immediately preceding his retirement, he
did not eat a single thing. I have examined a number of grizzlies that
were killed while hibernating, and in every instance the stomach and
intestines were empty. These facts lead me to conclude that bears rest
and fast for a few days before going permanently to the winter den.
The bear generally prepares his winter quarters in advance of the time
needed. He may occasionally sleep in his den before taking possession of
it for the winter. But this is exceptional. In two cases that I know of
he lay outside the den, though near it; and a number of other times he
kept away from the den until he entered it for the long sleep. After the
den is completely ready, the grizzly continues his usual search for
food. Generally this requires long excursions and he may wander miles
from the den.
In climbing along the bottom of a deep, narrow ravine one November day,
I saw on the slope above me what appeared to be a carload or more of
freshly dumped earth. My first thought was that a prospector was at work
driving a tunnel; but upon examination it proved to be a recently
finished but not yet occupied hibernating-den. The entrance was about
three feet in diameter. Just inside the den was a trifle larger. It
extended, nearly level, about twelve feet into the mountain-side. At the
back it was six feet across and four feet high.
The size of the den varies and is apparently determined by the character
of the soil in which it is made and also by the inclination of the bear
making it. Most other dens measured were smaller than this one.
The grizzly may use the same den for several winters or have a new one
each year. He may dig the den himself or take an old one that some other
bear has used, or he may make use of one shaped by Nature--a cave or a
rock-slide. I knew of one grizzly hibernating in a prospector's
abandoned tunnel. Sometimes, like the black bear, he will dig a den on a
steep mountain-side beneath the widely spreading roots of trees;
sometimes beneath a large fallen log, close to the upturned roots which
support it. In crossing the mountains one February I noticed a steamy
vapor rising from a hole in the snow by the protruding roots of an
overturned tree. I walked to the hole to investigate. The vapor was rank
with the odor of a bear. Near my home on the slope of Long's Peak I
have known grizzlies to den up beneath the snow-crushed, matted
tree-growths at the timber-line, at an altitude of about eleven thousand
feet.
Twice I have known bears to hibernate in enormous nests that were made
of the long fibres of cedar bark. It must have taken days to construct
one of these nests, as more than forty cedar trees had been more or less
disrobed to supply material for it. It resembled the nests of trash that
razor-back hogs in the South construct, though much larger. The bear,
after piling it up, worked his way in near the bottom, somewhat after
the fashion of a boy crawling into a haycock. Over this hibernating-nest
the snow spread its blanket and probably afforded all the protection
needed.
Sometimes the entrance to a den is partly closed by the occupant. Once
in, he reaches out and claws the lower part full of earth, or rakes in
trash and leaves. In most instances nothing is done to close the
entrance. The snows drift back into the den, pile upward, and at last
close the entrance most effectually.
All the dens that I recall were upon northerly or easterly--the
cooler--slopes. The snow as it fell would be likely to remain and close
or blanket the entrance all winter long. Snow evidently enters into the
grizzly's winter plans.
Late one cold, snowless December I came upon a grizzly carrying spruce
boughs into his den. Evidently he had used the den and found it cold.
The den had a large opening; this he may have been intending to close.
The rocky floor was already piled a foot deep with boughs. I have seen
two other dens with floor-coverings; one of these was of pine twigs, and
the other of coarse grass and kinnikinnick. But in most cases the bear
sleeps upon the uncovered rocks or the naked earth.
Snow is a factor in determining when a bear begins his winter sleep. If
he is fat and food is scarce, an early, heavy snow is pretty certain to
cause him to turn in early. If no snow comes and food is still to be
had, the bear is likely to delay his hibernation.
The individual inclination of the bear and his condition--whether fat or
thin--are also factors which influence his time of retiring. I knew of
two bears, apparently of similar condition, one of whom turned in three
weeks earlier than the other. Two bears whom I noticed one winter ran
about more than a month after all the other bears had disappeared. Both
were thin--just why I should like to know. They also turned in shortly
after they became rounded out. Generally bears of a locality turn in for
winter at about the same time. Hibernating may begin early in November,
but in most localities, and in most years, the time is likely to be a
month later.
In Alaska and the Northwest many bears hibernate in the heights above
the timber-line. I have found a number in the mountains of Colorado with
winter quarters at an altitude of twelve thousand feet. In southern
Colorado and in the Yellowstone Park region many have denned up at about
the altitude of six thousand feet. But a grizzly may hibernate anywhere
in his territory where he can find or make a den to his liking.
Except when there are cubs, a grizzly dens alone. Accounts which tell of
a number of full-grown grizzlies spending the winter in one den lack
verification. The cubs are born in the hibernating-den, and they den up
with the mother the first, and sometimes the second, winter after their
birth. The cubs generally den up together the first winter after they
are weaned.
Once in for the winter, the bear is likely to stay in the den for weeks.
Most of the time probably is spent sleeping, and, so far as known,
without either food or water. A bear may be routed out of his winter
quarters without difficulty. Generally his sleep is not heavy enough
greatly to deaden his senses. Hunters, trappers, floods, and snow-slides
have driven grizzlies from their dens during every stage of hibernation,
and in each case a moment after the bear came forth his senses were as
alert as ever; he was able either to run away or to fight in his normal
manner.
Prospectors in Jefferson Valley, Montana, told me of staking claims and
starting to drive a tunnel early one December. A day or two after they
began blasting they saw a bear break out of a snowy den and scamper away
on the mountain-side. They tracked him to the place where he had holed
up again. It was their belief that the noise or the jar of their shots
had awakened and re-awakened the bear, until, disgusted, he left the
region for a quieter sleeping-place.
A sniffling and grunting attracted my attention one midwinter day as I
was snowshoeing along the side of a ravine. Presently, a short distance
ahead of me, I saw a grizzly's nose thrust out of a hole in the snowy
slope. Then his head followed. Sleepily the grizzly half-opened his
eyes, then closed them again. His shaking and drooping head fell lower
and lower, until with a jerk he raised it only to let it droop again. He
repeated this performance a number of times. Evidently it was the head
of a very sleepy grizzly. Occasionally he opened his eyes for a moment,
but he did not seem interested in the outside world and he finally
withdrew his head and disappeared in the den.
After midwinter, and especially towards spring, a bear sometimes comes
out for fresh air and exercise, or to sun himself. One gray February
day, snowshoeing along the Big South Poudre, I chanced to look across an
opening from the edge of the woods and saw a grizzly walking round and
round in a well-beaten pathway in the snow. Occasionally he reared up,
faced about, and walked round in the opposite direction. His den was
near by. Half a mile farther on I came upon a bear trail near the
entrance to another den. Here the bear had walked back and forth in a
pathway that was about sixty feet long. It was beaten down in the snow
to a depth of fifteen inches. Two places showed that the bear had
rolled and wallowed about in the snow.
Elsewhere, another year, about the middle of March, I examined much-worn
pathways near a grizzly's den. These had been made at least three weeks
before and had been used a number of times. One pathway led to the base
of a cliff that faced the east, where the bear had probably lain in the
morning sun. Another led to a much-used spot that caught the afternoon
sun.
Perhaps a bear sometimes becomes tired or restless during his long
winter sleep. Now and then he comes forth in spring with the fur worn
off his hips, back, or shoulders. He may kill time, when through
sleeping, with a short excursion outside the den. If the den is large,
he sometimes tramples about like a caged animal.
Climatic conditions, the altitude at which the bear hibernated, and
other factors determine the time when grizzlies leave their dens. Most
of them come forth during March, but stragglers may not appear until
late in April. Mothers with cubs remain in the den a few weeks longer
than bears without cubs.
At the limits of tree growth, one cold March day, I came upon the tracks
of a grizzly bear descending the mountain. I back-tracked them and
found the den in which the grizzly had spent the winter. The inside of
the den was gravelly and comparatively clean. Only this single line of
tracks led from the den, though the weather had been clear for a week;
so I judged this was the first time the grizzly had sauntered forth. It
was just sundown when I reached the den. The heights were icy, and I
hesitated about continuing across the Divide that night, so concluded to
occupy the den. I knew that bears often take a short ramble in the
spring and then return to the den, but I took the chances of sharing it
with him. I do not know what the grizzly did that night--whether or not
he came back. But my fire in the mouth of the den may have kept him at
bay.
The hard, cracked skin on the soles of the grizzly's feet is shed during
hibernation, and the feet in spring are soft and tender. For several
days he avoids traveling over rough places. His claws grow out during
the winter rest, also. When he goes to sleep they are worn, broken, and
blunt; but he comes out of winter quarters with claws long and
moderately pointed.
What is the grizzly's condition in the spring after months of fasting?
He has hibernated from three to five months, and in this time probably
has taken neither water nor food. First of all he comes forth fat and
not in the least hungry. The walls of his stomach have greatly
contracted, almost completely closing the interior. Two stomachs which I
saw taken from grizzlies killed early in the spring were as hard as
chunks of rubber, and had capacity for not more than two or three
spoonfuls. But when the grizzly reappears after his long winter sleep he
is as strong as ever and can run for hours or fight with normal
effectiveness.
He may not eat anything for a few days after leaving the den. For many
days he eats lightly, and it may be two weeks before he has a normal
appetite. His first food is likely to be the early, tender shoots of
plants or trees, tuberous roots, swelling buds, and green grass.
I once watched a grizzly for seven days after he emerged from his
hibernating-cave. His winter quarters were near timber-line on Battle
Mountain, at an altitude of nearly twelve thousand feet. The winter had
been of average temperature, but with scanty snow-fall. I saw him, by
chance, just as he left the den, on the first day of March. He walked
about aimlessly for an hour or more, then returned to his sleeping-place
without eating or drinking anything.
The following day he wandered about until afternoon before he broke his
fast. He ate a mouthful of willow twigs and took a taste of water. He
walked leisurely down the mountain and towards sundown made himself a
nest at the foot of a cliff in the woods. Here he remained, apparently
sleeping, until late the next afternoon. Then, just before sundown, he
walked out a short distance, smelled of a number of things, licked the
snow a few times, and returned to his nest.
The fourth day he went early for water and ate more willow twigs. In the
afternoon he came upon a dead bird,--apparently a junco,--which he ate.
After another drink he lay down at the foot of a tree for the night. The
following morning he drank freely of water, surprised and devoured a
rabbit, and then lay down. He slept until noon the next day, then set
out foraging; he found a dead mouse and toward evening caught another
rabbit. The seventh day was much like the preceding one. During the
first week out the grizzly did not eat food enough to make him one
ordinary meal.
Hibernation is not well understood. The habit probably originated from
the scarcity of food. However, in Mexico grizzlies sometimes hibernate
even though the climate be mild and food plentiful. As these grizzlies
probably came from the cold north, the habit may have been fixed in the
species when it arrived. Hibernation appears to be helpful and not
harmful, and it may therefore continue for ages even though not
required. The rest which hibernation gives to mind and stomach, with the
entire organism relaxed, may both increase efficiency and lengthen life.
The polar bear has its own peculiar hibernating-habits. The food of this
bear is sea food. This is available even in the winter-time, on or
beneath the ice. The male polar bears do not hibernate; the females do
not except when about to give birth to young. The cubs at birth are
small and helpless, and require the mother's constant care and the
shelter of the den for some weeks after birth.
Mr. J. D. Figgins has written one of the best comments on hibernation
that I have read. I quote as follows:--
"The period of hibernation in any mammal not only varies in a given
species, but is largely influenced by the available supply of food
to which it is accustomed or that is necessary for its requirements.
"Examples of this character may be cited among several species of
mammals. It is the custom of the chipmunks, or 'ground squirrels,'
to hoard up at least a partial supply of food in the autumn for
consumption during the winter months; but this is rarely, if ever,
sufficient to keep these interesting little animals active for the
entire period. In most localities, there is no available food with
which to augment their scant store and they are never in evidence
from late October to April. In other locations where the fruit of
the Cratægus, or 'thorn apple,' is to be had, they may be seen
almost daily, although the ground may be covered with several feet
of snow and low temperatures prevail.
"Another example is the opossum. Ordinarily these animals are active
throughout the entire year, but towards the northern edge of their
range they frequently hibernate for considerable periods (thirty-one
days from personal observations).
"Certain of the small rodents can, and probably do, hoard sufficient
food for actual need during the winter months; but the problem is
in direct ratio to the size of the animal. Hence we find the marmot,
a much larger animal, making no provision, although his habitat is
confined to the higher altitudes and his period of hibernation is
extended over a greater length of time than many other species. His
food consists wholly of grass and other green plants, and it is
doubtful if he could subsist on dry food. Granting that he could,
the amount required would be prohibitive, otherwise he would make
some effort in that direction, as do the conies, a much smaller
animal.
"Being omnivorous and of great size, a bear could not secure or
preserve the necessary amount of food to carry him through five
months. Such food could not consist of any variety other than
vegetation, and he is not a 'hay' eater, and so, nature has provided
him a means of surviving the long period of fasting and probably,
without discomfort.
"It is well known that bears show a distinct preference for fruit
during the late summer and autumn months. Not because that is the
season for the various fruits, but through a need of their sugar
content and its fattening qualities. Composed largely of juices
which are quickly absorbed, the digestive process is very brief and
the discarded residue is discharged at once. This may give rise to
the belief that a purgative has been employed as a means of
cleansing the bowels and explains the presence of unbroken berries
in the excrement and the absence of offensive odors. As a means of
exploding the purgative theory we need only refer to bears in
captivity. Although the latter may be confined to cement floors and
have no access to any matter whatever, other than the food regularly
supplied, they frequently hibernate in a quite orderly manner.
"It must be conceded that bears are irregular in the period of
'holing up' and that they do so only when food has become too scarce
to sustain activities without a drain upon the store of fat they
have acquired; or during very severe weather. In the mean time there
has been a gradual reduction in food as the period of hibernation
approaches and a consequent lessened activity of the bowels. Nor is
there reason for surprise because of the absence of excrement in the
burrow and the presence of matter in the rectum when the bear
emerges in the spring.
"In captivity bears may, or may not, hibernate. As a rule they
'sleep' for more or less varying periods during severe weather. One
authority states the grizzly has been known to sleep from sixty to
seventy-five days and during that time it was not difficult to
awaken him. Black bears frequently pass the winter without evidence
of even drowsiness. Others awake at irregular intervals, and after
feeding lightly, return to their slumber."
The winter life of many animals is stern and strange. During the autumn
the beaver stores up a food-supply for use when the pond is closed over
with ice. The cony harvests hay for his winter food. Numbers of animals
hunt food each day in the snow. But the woodchuck and the bear
hibernate, that is, they fast and sleep in a den during the winter.