Mammals can also generate little bursts of heat by shivering, and shivering costs the bird, however, by depleting energy stores. Given these facts, how can mammals generate heat among the following options:
- layers of fat
 - Ice cubes
 - wishing
 - Depleting energy stores
 - death
 - with their fur
 - raising their temperature
 - by keeping them warm


 

    Depleting energy stores     