But how the squirrels know that a masting event is going to occur is a mystery. The clue might be the buds that the trees produce 18 months before. In a masting year, most of the buds will become cones, not new branches. The squirrels may be able to tell visually that the buds will become cones or they may get chemical cues, in the form of plant hormones, when they eat some.
—Henry Fountain / NYT