72 DEPARTMENT OF AGRICULTURE. [Pub. Doc. 



in diameter were not usually found to have been worked upon. However 

 destructive this drilling would seem to be, it does not seriously affect the 

 vitality of the trees; the pits are but 4 to 5 mm. deep, penetrating only 

 the outer layers of the bark, which after a time scale off. We would judge 

 that all evidence of this woodpecker's work is thus removed in natural 

 process within about three years. The heartwood (sapwood?) seems to 

 be not damaged at all, as is the case with most true Sapsucker work. 

 Our inference is that the Willow Woodpecker feeds on the inner layers of 

 bark, which the bird exposes through the perforations above described. 



