Holes drilled by a Red Breasted Sap Sucker

A sapsucker’s tongue is adapted with stiff hairs for collecting the sap. Red-Breasted Sapsuckers visit the same tree multiple times, drilling holes in neat horizontal rows. A bird will leave and come back later, when the sap has started flowing from the holes. Repeated visits over an extended period of time can actually kill the tree.[3] The insects attracted to the sap are also consumed, and not only by sapsuckers. Rufous Hummingbirds, for example, have been observed to follow the movements of sapsuckers and take advantage of this food source.

drilling of sapsuckers is related to the underlying physiology of the tree.

Sapsuckers obtain theirs [sap] by repeated wounding. This leads to an increased flow of nutrients, an effort of the tree to repair the injury that nutrients will accumulate above a girdle, as indicated by a layer of thickened wood.