THE WOODPECKERS, KINGFISHERS, AND CUCKOOS. 189 



done by the spruce-destroying bark-beetle (Dendroctonus 

 piceaperda), but that its work was being largely checked by 

 woodpeckers, probably chiefly the Arctic Three-toed Wood- 

 pecker and the Banded Three-toed Woodpecker, as these 

 species come from the far North in winter and live in 

 northern New England in numbers. Dr. Hopkins writes : 

 " Woodpeckers are the most important enemies of the bark- 

 beetle, and appear to be of inestimable value to the spruce- 

 timber interests of the Northeast. Indeed, I feel confident that 

 in the many hundreds of infested trees examined, at least 

 one-half of the beetles and their young had been destroyed 

 by the birds, and in many cases it was evident that even a 

 greater proportion had perished from this cause alone. 



" Estimating one hundred beetles to the square foot of 

 bark in the average infested tree and an average of sixty 

 square feet of infested bark, it is possible for each tree to 

 yield an average of six thousand individuals, one hundred 

 trees six hundred thousand, and so on. It is therefore plain 

 that if one-half or two-thirds of this number are destroyed 

 by the birds and other enemies, the amount of timber the 

 remainder can kill will be lessened. This is all the more 

 apparent when it is remembered that it is only when the 

 beetles occur in great numbers that they can overcome the 

 resistance of the living trees." 



In California, however, Dr. Hopkins has found the wood- 

 peckers to be in some respects of doubtful utility in their 

 relations to forest insects. There certain clerid beetles and 

 other enemies of bark-borers are abundant, and are especially 

 exposed to the attacks of woodpeckers. The result is that 

 they are eaten to a large extent and so are prevented from 

 killing the bark-beetles. 



The Yellow-bellied Woodpecker, or true Sapsucker, either 

 in the typical or a varietal form, occurs throughout the United 

 States. Although seldom an abundant species, it is rather 

 common within its range. The structure of its tongue differs 



