Recently I have been receiving calls about trees that look like they have lines of holes in the bark and no evidence of insects that cause the problem... There is good reason for this as the damage was not caused by insects. It was caused by the Yellow Bellied Sapsucker. (see Photo of Damage)
This bird creates several holes in the tree and uses them to lick up sap as it bleeds from the wound. In most cases the wounds are shallow just breaking through into the sap layer of the tree and causes the sap to ooze out. Once the sap comes out the bird eats the nutritious material for nutrients.
In most cases this does not kill the tree as the tree quickly seals off the hole, therefore the large number of holes. In some cases if a Sapsucker takes favor of your tree it may weaken it and cause concern, but in most cases this is not the case. A larger concern is the opening of the bark and allowing insects and disease easier access into the tree.
The most common trees I see them favoring include: apple (especially crab), maples, mountain ash and willows. In some cases you can protect the tree by wrapping the trunk with hardware cloth or burlap to try and discourage them from feeding.
For additional information check out these websites:
Controlling Nuisance Woodpeckers (Missouri Extension)