WOODPECKERS IN RELATION TO TREES AND WOOD 
PRODUCTS. 
INTRODUCTION. 
Woodpeckers are peculiarly dependent upon trees, winch furnish 
them food, shelter, and cradles for their young. Xo birds are more 
highly specialized nor more perfectly adapted to a particular mode 
of life than are most woodpeckers to arboreal existence. Moreover, 
as trees are important to woodpeckers, so are these birds important 
to trees. Woodpeckers benefit trees by consuming many of the most 
destructive forest pests, insects largely inaccessible to other birds. 
In securing these insects, however, which constitute the bulk of their 
food, and in making nests and shelter cavities, woodpeckers have 
another significant economic relation to trees, for they remove bark 
and wood from both dead and living trees. In the case of dead trees 
little or no harm is done. When, however, they make excavations in 
living trees, the birds destroy more or less of the cambium layer, 
from which proceeds the growth of both wood and bark. Slight 
injuries to the cambium result in distorted growth, but the destruction 
of large areas may cause death. Since trees are exceedingly valuable 
to man, the habits of birds whose relations to trees are so vital are 
of much economic importance. 
It is the purpose of this bulletin to examine the evidence for and 
against woodpeckers and to determine their status according to the 
effect of their habits upon trees and wood products. Injuries by 
woodpeckers are treated under two heads: (1) Damage by wood- 
peckers in general; (2) injuries due almost exclusively to the three 
species properly known as sapsuckers. 
DAMAGE BY WOODPECKERS IN GENERAL. 
This topic may be divided into two sections: Damage to trees, 
and damage to wooden, posts and structures. 
DAMAGE TO TREES. 
Primarily the work of woodpeckers on the living parts of trees is 
injurious. The important cambium layer is injured every time a 
nest is excavated or an insect dug out. To what extent the various 
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