The birds drill into the bark in order to release the sap from inside, hence their name. These interesting hole designs - that also can be rows of squares - do not damage the tree.
Hummingbirds are attracted to sapsucker holes not to consume sap, but to feed upon the insects that are also drawn to the sweet liquid. The insects provide a valuable source of protein for Ruby-throated Hummingbirds as they migrate northwards to their breeding grounds.
It's amazing that the efforts of one sapsucker can have such wide-reaching affects!
photo © adrian binns