What is a Woodpecker?:
Many woodpeckers are tree bark feeding birds with unique clinging feet, long tongues and specialized beaks designed to help with communicating the possession of territory to rivals and locating and accessing insects. This is done mostly by tapping and pecking noisily on tree trunks with their beaks. The woodpecker's long tongue, in many cases as long as the woodpecker itself, can be darted forward to capture insects from the inner and outer bark.
How a Woodpecker Feeds:
A woodpecker searches surfaces of tree trunks and branches for wood boring beetles, carpenter ants, and other insects. The pecking style used for feeding is very different than territorial drumming which is done mainly in the Spring.
Only a few pecks are made and then the bird explores the resulting hole with its specialized bill and tongue. This behavior continues until an insect is found or the bird is satisfied that one is not there. Then the woodpecker may hop a few inches away and peck at another place. The damage from this feeding activity often occurs in horizontal lines.
Woodpeckers Seek Tree Cavities and Rot:
In most cases, a woodpecker prefers dead wood rather than sound wood to dig for food or excavate nest cavities. Since most trees contain some dead wood, the woodpeckers' activity doesn't necessarily mean the tree is being harmed by the bird.
Sapsuckers Vs. Woodpeckers:
Not all Woodpeckers seek insects for food. A sapsucker is a woodpecker that prefers sap but will eat insects attracted to the sap. The United States Forest Service suggests that the American yellow-bellied sapsucker will attack and kill trees and seriously degrade wood. The sapsucker is a serious tree pest, it is migratory and effects trees through out North America. The USFS study concludes that a sapsucker will kill red maple nearly 40 percent of the time it attacks where as it only kills hemlock at the rate of 1 percent.
Insect eating woodpeckers are less of a problem than sap eating woodpeckers. They tend to only feed and nest in dead wood and are generally considered harmless to a tree.
Sapsuckers, on the other hand, attack living wood and often return to the tree to increase the size of the holes for fresh sap. Repeated attacks can girdle and kill branches or the entire tree. Insects, porcupines, or squirrels may be attracted to the oozing sap and cause additional injury. Wood decay or stain fungi and bacteria may enter through the feeding wounds.
How to Discourage a Feeding Sapsucker:
To discourage sapsuckers from feeding on your tree, wrap hardware cloth or burlap around the area of attack. You can also smear on a sticky repellent such as Tanglefoot Bird Repellent. Tree Guard Deer Repellent is also said to discourage feeding when sprayed on the tapped area. Remember that they may choose another nearby tree for future tapping. It may be better to sacrifice the tapped and already damaged tree in favor of the loss of another tree due to future tapping damage.