When survival is challenged by the cold, animals react by employing both behavioral and physiological solutions. Depending on the magni tude of the cold stress and the nature of the adjustment, simple avoidance or sophisticated capacity or resistance compensations may be used. Thus, migration, shelter seeking, metabolic and insulative compen sation, torpor, and freezing avoidance and tolerance are successful tac tics used by diverse groups of animals. To understand and appreciate the benefits of these tactics, it is necessary to examine not only the well being of the whole animal but also...