Mysterious Holes in Trees

I recently received an email with a photo of a pine tree attached.  The message was simple: "Would you happen to know what this is on a pine tree?"  When I looked at the photo, I instantly recognized the small holes that were drilled into the tree in a distinct pattern as damage from a yellow-bellied sapsucker.

Sapsuckers are members of the woodpecker family and are migratory birds. In Pennsylvania, they are common when they arrive in the spring but usually spend the summer months further North. During the fall of the year, they return to Pennsylvania on their way south. It is somewhat rare to find a resident sapsucker in the winter in Pennsylvania.

Sapsuckers feed by drilling holes through the bark to the cambium layer. This causes sap to begin to flow from the wound and they will then feed on that sap. The birds may visit the tree several times each day to feed and return for several days. In addition to the sap, sapsuckers will also feed on small insects that are attracted to the sap. The holes that are drilled through the bark are in a very orderly pattern consisting of parallel rows that are evenly spaced apart.  Sapsuckers may drill up to thirty holes each day and trees may have multiple bands of holes from consecutive years of feeding on the same tree. 

In the mid-1960s there was a study done by the USDA Forest Service to document the extent of the damage caused by sapsuckers and which tree species were preferred by the bird. The observations were mostly in Maine but there were also locations in New York and Northern Pennsylvania. The forest type that was studied was primarily Northern Hardwoods. The study found that the number of tree species that sapsuckers feed on is numerous and it can vary by the time of year and even how much rain falls during the time the birds are present.

In this study, there were twenty-eight different tree species that sapsuckers had been observed feeding on, but other studies showed as many as one hundred seventy-four. The top three tree species were paper birch, red maple, and Eastern hemlock. The study found that hemlock, spruce, and aspen were used early in the spring but by late spring the feeding became more prevalent on red maples. During summer, the birch trees were the preferred species. It was noted that during dry summers, feeding tended to shift away from the birch and other hardwoods, back to the hemlocks until it began to rain again, presumably due to moisture stress in the hardwoods.

Typically, sapsuckers do not kill mature, healthy trees however some mortality has been observed. It is often smaller trees or branches that succumb to excessive sapsucker feeding. Because the birds spend a relatively short time in Pennsylvania, mortality is low. The feeding activity can affect the quality of the wood that comes from the trees when they are harvested and sawn into lumber. The way a tree heals a wound is to grow new wood over the top of the wound.  As the tree grows, the defect gets more "good" wood over top of it and eventually the defects will end up in the quality zone of the log where the lumber is sawn from. In lumber, this is called bird peck. In addition to bird peck being a defect in lumber, the holes the sapsuckers drill can sometimes become discolored and affect the quality of the wood as well. 

There are not many options for controlling sapsucker damage. They are protected by state and federal law, so it is illegal to harm or kill them.  If there are a few trees of particular concern, an option is to wrap the stem of the tree in a heavy cloth covering or burlap while the birds are migrating through in the spring and fall but be sure to remove it once they have moved on to prevent other types of injury to the tree.  Another option is to hand an owl or hawk decoy in nearby trees to scare them off.