Q. What keeps squirrels from gaining huge amounts of weight as they gorge on acorns and nuts each fall?

A. In fact, many squirrels do achieve huge weight gain ahead of the privations of winter.

Common gray squirrels may increase their weight by 25 percent in the harvest season. But not because they hibernate — they don’t.

Winter foraging is hard, and gray squirrels tend to spend the winter months mostly in their nests. But they must make forays every few days to seek squirreled-away food and other nourishment.

Among hibernating squirrels, much of the stored nourishment is needed to survive the cold season without foraging. A study of the Arctic ground squirrel found extreme weight gains during the active season: 42 percent among males and 63 percent among females. They slow their activity drastically before hibernating in order to maintain peak mass.

While some do emerge from winter lighter, a significant share of their fat stores may remain.

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