A tell-tale sign of Yellow-bellied Sapsucker activity is the presence of rows of 1/4–inch holes, often drilled in Sugar Maples and birch trees in order to gain access to their nutritious phloem sap. Once the sap begins to flow, sapsuckers insert their tongues into these holes. Here is where their name is misleading, as sapsuckers don’t actually suck the sap, they lap it up with the aid of tiny hair-like projections on the edge of their tongue, which hold the sap by capillary action (see insert). Each flick of the tongue brings more sap into the woodpecker’s mouth.
Because sap is so essential to a tree, wounds are quickly healed over to prevent loss of sap. Scientists still have not figured out how sapsuckers overcome a tree’s defenses and maintain a continuous flow of sap. One theory is that sapsucker saliva may contain a substance that acts as an anticoagulant, preventing sap from clogging up and sealing over the holes the bird creates.
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