A stocky body for carrying fat and minimizing heat loss in winter
Ability to grow dense insulating fur
Ability to accumulate excess fat when food is available and remain healthy doing so
Ability to reduce their metabolism (hibernate) in seasons of scarcity.
Ability to mate when food is scarce in late spring and early summer, delay implantation of the blastocyst until November, give birth in the den in mid-winter, and in many ways arrange their annual life cycle of behavior and physiology to maximize efficiency of feeding during the time of year when food is most available.
