FOOD OF WARBLERS 23 



in regard to this subject exists that some variation from this time 

 will doubtless be found. 



The young are cared for by both parents and leave the nest 

 when from eight to twelve days old, or on the completion of the nestling 

 plumage. In most cases but one brood is reared. 



FOOD OF WARBLERS 



BY EDWARD HOWE FORBUSH 



It is no exaggeration to say that for the preservation of the 

 forests, which supply the raw material for nearly all wood products, 

 man is largely indebted to birds. The service that birds perform 

 in protecting woodland trees against the inroads of injurious 

 insects is more nearly indispensable to him than any other bene- 

 faction that his feathered friends confer, for the money value of 

 woods, while great in the aggregate, is not ordinarily large enough 

 to repay the owners the expense of protecting the trees against 

 insect enemies, even were this possible. 



A single species of insect may be too much for man to cope 

 with when it infests his woodland. The wild animals and venom- 

 ous serpents of the woods he may exterminate ; but, in spite of all 

 his efforts, insects, dangerous to human life or destructive to 

 property, still infest the land. 



Dr. A. S. Packard enumerates over four hundred species of 

 insects that feed upon our oaks. All other forest trees have many 

 enemies of their own. Insects attack all parts of the tree, and in so 

 many insidious ways that man cannot hope to check them all. 

 Were the natural enemies of insects annihilated, every tree of the 

 woods would be threatened with destruction and we would be 

 powerless to prevent the impending calamity. We might save a 

 few orchards and shade trees ; we might find means to raise some 

 vegetables; but the protection of all the trees in all the woods 

 would be beyond our powers. 



It may be profitable to spray orchards with insecticides but 

 it does not pay to spray wood-lots ; to say nothing of the expense 

 of the manual labor that must be utilized in combating insects that 

 cannot be reached by ordinary insecticides. So we must leave 

 the protection of the woods to birds and other natural enemies of 

 injurious insects. 



Birds attain their greatest usefulness in woodlands, mainly 

 because the conditions prevailing there closely approach the nat- 



