WOODPECKERS 



319 



rows. On this particular trunk, the pits occurred over a vertical distance 

 of 41 inches (105 cm.), so that there were about 2100 pits in all on this 

 one tree. Limbs less than 4 inches (10 cm.) in diameter usually had not 

 been worked upon. However destructive this drilling may seem to be, it 

 does not seriously affect the vitality of the trees ; the pits are but 4 to 5 mm. 

 deep, penetrating only those outer layers of the bark which after a time 

 scale off. We should judge that all evidence of this woodpecker's work 

 is thus removed through natural process within about three years. The 

 heartwood of the tree therefore seems not to be damaged at all by the wood- 

 pecker 's work ; it is damaged, however, by the work of the true sapsucker. 









Fig. 41. Drillings by Willow Woodpecker in outer layers of bark of apple tree in 

 Yosemite Valley. Photographed November 8, 1915; about ^^ natural size. 



Our inference from these facts is that the Willow Woodpecker feeds 

 on the inner layers of bark, which the bird exposes through the per- 

 forations described above. We watched a bird at work; moreover, bits 

 of inner bark-fibers were found adhering to the bristles around the bill of 

 a bird shot. 



NuTTALL Woodpecker. Dryobates nuttalli (Gambel) 



Field characters. — Size small for a woodpecker, little over half that of Modoc 

 Woodpecker. Whole back, wings, sides of body, and outer tail feathers barred or 

 spotted with black and white; throat and breast white, unmarked; head black, with a 

 white stripe above and another below eye; back of head red in adult males. Juvenile 

 birds of both sexes have more or less red on crown of head. Flight course in short 

 swoops or undulations, with intermittent wing strokes. Voice: A loud, high-pitched trill. 



