What's the relationship between woodpeckers and trees? Does the bird's drilling hurt or help the tree?
We have fourteen woodpecker species in Canada. Some common species in our area are downy and hairy, and the largest, pileated woodpeckers (Picoides pubescens, Picoides villosus, and Dryocopus pileatus), as well as yellow-bellied sapsuckers (Sphyrapicus varius) and northern flickers (Colaptes auratus).
First
of all, most woodpeckers nest in already dead cavities of trees, or in
standing dead wood. (Some species actually prefer man-made birdhouses!)
Insect-eating species, like our most common downy woodpecker, will feed
in bark crevices. The woodpeckers who bore holes to feed are harvesting
from a tree that already has an insect presence. This is just nature
doing its thing.
If it's spring and you hear "drumming" on parts of your house, don't worry--it's most likely a territorial male sending out signals in the nesting season. He's not actually boring holes in your house. (Though, there are instances where peckers will damage a home while foraging or nesting, so look for the holes as evidence of a real problem)
Sapsuckers are a different story. As the name suggests, they drill holes in patterns to harvest sap from the tree. They have a strong preference for white birch, which has a high sugar content. Though sapsuckers will return to the same tree and holes to feed, the systematic drilling of patterned holes can eventually girdle a tree--although, research has shown that sapsuckers can detect "stress" in a tree, and actually prefer trees that are already in decline. (Stressed trees produce more sap as a defense mechanism, so it makes sense that the sapsuckers prefer this.) They are migratory so they only hang around our area in the summer.
A word to homeowners with fruit trees: though they prefer birch, sapsuckers also like to drill fruit trees. You can deter sapsuckers by wrapping vulnerable tree trunks, but if you notice the systematic drilling pattern of a sapsucker on only one tree, you might as well leave it. If deterred, the sapsucker might simply choose a nearby tree to begin drilling again. When it comes down to it, woodpeckers are following the natural order, and seem to choose sustainable lifestyles (i.e., nesting in dead wood, and feeding from already stressed trees). Enjoy the birds!
