KEEPING WARM 
bears lose weight. Grass, which bears 
eat in great quantities in the spring, is 
not easily digestible. Black bears in my 
study area begin to fatten up for winter 
in June, with the ripening of carbohy- 
drate-rich berries. The bears’ weight 
gains in summer depend mainly on the 
availability of good crops of blueberries, 
cherries, wild sarsaparilla berries, and 
hazelnuts. When these and other digest- 
ible foods disappear in September, en- 
ergy conservation becomes the rule until 
the following May or June. 
One exception to this rule concerns 
bears that are miles outside their usual 
home ranges when food becomes scarce 
in the fall. They have to expend consid- 
erable energy returning home for win- 
ter. A 450-pound, eleven-year-old male 
that was 1 19 miles from home on Octo- 
# 
ber 1 5 made the trip back in nine nights, 
going straight to a den. A second way in 
which black bears expend, rather than 
conserve, energy in the fall is by prepar- 
ing a different den each year. Why they 
do this — often with the den of the previ- 
ous year still intact — is anybody’s guess. 
In one case, a fifteen-year-old pregnant 
female with access to two rock caves she 
had used in previous winters chose in- 
