This appears to be the work of Sapsuckers (birds). They are very active in spring, pecking regular patterns of holes. They are making the sap flow and then repeatedly return to feed on the sap. The sap also attracts insects and the sapsuckers feed on those insects too. Here is more information about sapsuckers and woodpeckers to help you diagnose what you have going on and options.
http://extension.oregonstate.edu/question-of-the-week/who-making-my-trees-holy
http://cru.cahe.wsu.edu/CEPublications/FS057E/FS057E.pdf  
For further advice on this, I recommend working with the Clackamas Master Gardeners at <personal data hidden><personal data hidden>
 Best wishes,