Oct. 15,1925 
The Hibernation of Ground Squirrels 
763 
On this date she was entirely in hibernation, but showed signs of 
wakening. She was observed almost daily from November 12, 1911, 
to March 13, 1912. Her subsequent behavior is as follows: 
She was awake and warm on November 12, 13, 23; December 7; 
February 23, 24; March 6, 7, 8, and 12. The hibernation period 
ended March 12. 
Her weights were as follows: 
Grams 
Nov. 18_466 
Dec. 2_450 
Dec. 9_441 
Dec. 16_ 441 
Dec. 30_425 
Jan. 6_ 420 
Jan. 13_420 
Grams 
Jan. 20_ 413 
Jan. 27_409 
Feb. 4_408 
Feb. ]7_399 
Feb. 25_ 385 
Mar. 2_387 
Mar. 9_370 
This squirrel was awake on five different occasions during the 
winter. She lost 90 grams in weight between November 18, 1911, 
and March 9, 1912. She was deprived of all food from November 
10 to March 13. 
INTERMITTENT AWAKENING FROM HIBERNATION 
As was shown by female 8, squirrels were wakening at intervals 
during the winter. Very careful daily observations relative to their 
condition revealed this fact. Males 8, 9; female 7, and Citellus 
townsendij male 5, all showed the same characteristic of interrupted 
hibernation. 
That they can pass in and out of the hibernation state rather easily 
is shown by Citellus townsendi No. 3, which, on November 8, was 
awake, November 9, in hibernation, and November 10 awake again. 
It was noted while making the daily observations that the squirrels 
would show signs of life and become somewhat warm occasionally 
without actually awakening. 
OBSERVATIONS ON AN AWAKENING SQUIRREL 
These animals are very lifeless in appearance and form when in the 
condition of hibernation. The eyes are very sunken and tightly 
closed. The mouth and lips are formless as in death. No sign of 
life remains, save a possible slow movement over the flanks, during 
which period the hairs of the region are slowly caused to bristle in 
erection. One in profound hibernation was removed to a warm 
room, and as she began slowly to show signs of life the following 
observations were made of her: 
At 3.20—Rhythmical thoracic respiration movements were notice¬ 
able. Mouth was opened slightly. 
At 3.32—Squirrel began to rub paws over her nose. Eyelids began 
to twitch. Body began to straighten out, and the front legs began 
to work in a writhing motion, from side to side, over the chest, the 
paws being held together about the middle of the belly. 
At 3.40.—This action was speeded up. The motion was fairly 
regular, suggesting the beating of the heart (the alternate contraction 
of auricle and ventricle). 
At 3.50.—Change took place. Up to this time very little or no 
movement of the hind legs and the hinder part of the body, but now 
the hind legs began to move. At this time, owing to the lateness 
of the day and failing photographic light, the squirrel was warmed 
by artificial heat. 
