Instead, the birds use their short brushlike tongues to drink the sap that oozes into the holes. They also eat the outer wood layers. As one row of holes becomes dry, another row is drilled, and so on. Rows of holes may extend for some distance up the trunk and heavier branches of the tree. Injury is usually most pronounced in the spring and early summer when sap pressure is greatest.
Damage varies considerably, depending on the persistence of attack.
Lightly attacked trees usually make a complete recovery. On the other hand, branches girdled with several rows of holes are often permanently damaged, and smaller trees or tops of trees may be killed by severe attack in several successive years. Harmful insects and disease organisms may enter the tree by way of these holes, resulting in secondary damage. The characteristic holes made by sapsuckers and the subsequent staining or discoloration of the wood can be recognized many years after the attack. Wrapping the damaged areas on individual trees with strips of burlap or other protective material and leaving it in place from April to late summer when the birds are most active is also effective.