That's very typical sapsucker damage. Birch is on their favorites list. They drill small round holes through the bark and into the vascular system of the tree. As the sap collects in the hole, the bird uses its specialized tongue to lap it up as well as any little ants or other insects that come to partake.

You can protect the tree by wrapping hardware cloth, window screen, burlap, or other breathable material loosely around the trunk to discourage the feeding. Don't nail those materials to the tree.

A small amount of damage won't do much damage, but if sapsuckers find a favorite tree, their aggressive feeding can actually cause problems.