Not a Nut
Like other nuts, an acorn is a seed, an embryonic tree-to-be wrapped in a hard shell. But only the lower end of an acorn's innards is occupied by a rudimentary root and stem; the rest is nutritive tissue loaded with protein, carbohydrates and fat. Its purpose is to sustain a sprouting seedling until the infant grows green leaves and can stock its own larder via photosynthesis. But far more often than not, a forest creature gobbles the nut and its stored nutrients first.
Upwards of 100 species of birds and animals include acorns in their diets. For many — including gray squirrels, blue jays, black bears, chipmunks, ruffed grouse and deer mice — nuts are the main food source, a critical element of day-to-day survival. For many more, acorns are a lifeline to spring and beyond. Without the benefit of the nuts' energy, those birds and animals will starve or fail to reproduce successfully.