bored by Yellow-Bellied Sapsucker birds。
https://www.google.com/search?q=holes+on+tree+bark&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiLgbmKvt3bAhUG3VMKHRHNBHcQ_AUICigB&biw=1605&bih=787#imgrc=fmLdf17ltTdJzM:
https://www.google.com/search?q=holes+on+tree+bark&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiLgbmKvt3bAhUG3VMKHRHNBHcQ_AUICigB&biw=1605&bih=787#imgrc=fmLdf17ltTdJzM: