Why do animals such as a hedgehog
hibernate during the cold winter
months?

To reduce heat loss

Explanation:

During cold weather, small animals like hedgehog survive by hibernating. During hibernation, the hedgehog go into a deep sleep and the metabolic rate falls to the minimum required for maintaining the vital activities of the cells. The body temperature is maintained at a lower level typically at about 18 c. These reduces heat loss.

well, i believe that the answer is 2. : 3