KEEPING WARM 
Bullaty Lomeo 
In northern Minnesota, black bears 
have from mid-April to mid-September 
to gain enough weight to carry them 
through the winter. While hibernating, 
the bears lose an average of 15 to 30 
percent of their body weight; lactating 
females lose as much as 40 percent. 
The mothers that lose the most weight 
are the ones with the heaviest litters. 
Most bears I observed left their dens 
in mid-April although mothers with un- 
dersized cubs sometimes delayed until 
early May. In years of light snow and 
early melt, some bears left as early as 
March 27. In northeastern Minnesota, 
however, the bears rarely, if ever, came 
out and wandered around on mild win- 
ter days. Spmehow the bears were not 
fooled by springlike conditions before 
March 27. In one case, during March a 
fourteen-year-old female had a problem 
with meltwater running into her den and 
soaking the nest that she and her two- 
month-old cubs were sleeping on. She 
left the den briefly and bit branches off 
several spruce saplings, bringing them 
back inside to pile onto the nest and 
raise the family above water. 
For several years Wilson, Konz, and I 
observed the activities of four family 
groups day and night as they emerged 
from their dens in April. They were 
active only by day, and their activities 
were much the same in all cases. The 
mothers began foraging within 150 
yards of their dens, leaving their four- to 
eight-pound cubs in the dens or playing 
around the entrances. The cubs re- 
treated into the dens at any strange 
sound, and their mothers returned every 
ten minutes or less to check on them. 
The mothers tore apart logs in search of 
beetles, grubs, and other invertebrates 
high in protein, climbed aspen trees to 
eat catkins, ate willow buds and grass, 
drank meltwater, and in one case con- 
sumed a deer carcass we had placed 
near the den. (Winter-killed carcasses 
are usually not available to bears in 
spring because they are cleaned up by 
wolves, ravens, eagles, and other scaven- 
gers before the bears emerge.) 
The mothers also spent a lot of time 
resting in or near their dens. When out- 
side, the cubs were very active, climbing 
small trees, stumps, or their mothers’ 
backs. Mothers nursed their cubs lying 
down or sitting up. One mother some- 
times sat leaning back against a support, 
cradling two of her cubs to her chest and 
licking the tops of their heads as they 
nursed. After a few days, the mothers 
moved their families to patches of snow- 
free ground at the bases of large trees. 
The ground was still frozen and the 
surface was wet with meltwater. As all 
bears do in early spring, the mothers 
constructed beds to rest on. With trees 
available for the cubs to escape into, the 
mothers would leave their cubs for an 
hour or more. 
With all the study of hibernating 
bears, a basic question remains: How do 
bears know when to go into or leave their 
dens? Certainly the bears live by some 
kind of internal clock, but what sets this 
clock — day length or some other cue — 
is unknown. Time of denning and emer- 
gence seems to vary to some extent with 
food supply, weather, and genetics, but 
how these and other possible factors 
interrelate is still a puzzle. For the Win- 
nebago Indians the answer was simple: 
the black bear is a clever and intelligent 
animal. □ 
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