The duck-billed platypus weighs between 2 and 5 pounds, and males are generally larger than females. Platypuses lose fat seasonally after the winter, making them lighter in the spring than in the fall. The average weight for adult males and females, regardless of season, is 3.35 pounds.
Their seasonal weight loss is an adaptation to cold weather. Although platypuses do not formally hibernate, they may enter a state known as "torpor" in the colder months. During torpor, the animals become completely inactive and their body temperatures drop. Platypuses may remain in this state for up to six days, living off of stored body fat.