This response was provided by Darryl Coates, Illinois Department of Natural Resources, District Wildlife Biologist.
The first step in handling a problem with wildlife is to identify the animal that is causing the problem. In my opinion, you could be blaming the wrong species. Birds like woodpeckers and sapsuckers may be looking for food and create rough drilled holes. Ground squirrels or tree squirrels may develop a taste for wood. Look for gnawing marks on the wood. However, if the hole(s) are perfectly round and fairly smooth, it is more than likely a wood boring insect like the Carpenter Bee. Take a picture of the damage and send it to your District Wildlife Biologist, Darryl Coates at Darryl.Coates@Illinois.gov or contact U of I CES in Bloomington to help you correctly identify the culprit. Thanks for writing.