American Forestry 



VOL. XXI 



JUNE, 1915 



No. 6 



BIRD ENEMIES OF FOREST INSECTS 



ByW. L. McAtee 



Biological Survey, U. S. Department of Agriculture 



BIRDS may be called health 

 officers for our trees. Wher- 

 ever unhealthy conditions pre- 

 vail as a result of insect attacks, 

 birds are sure to discover them and to do 

 something toward improving the situa- 

 tion. As surgeons examine human 

 bodies for evidences of disease and re- 

 move the cause, so birds tirelessly scan 

 the trees from top to base, detecting 

 insects and devouring them. As there 

 are specialists among the surgeons, 

 some paying particular attention to 

 one part of the body and others to 

 another, so with the birds in their 

 relations to trees. 



The ground feeding birds as the wild 

 turkey, grouse, che winks, wrens, and 

 thrushes, search the leaf strewn forest 

 floor and devour many insects injurious 

 to the trees. The woodpeckers clamber 

 about over the trunks and larger 

 branches, detect their prey beneath the 

 bark and dig it out. The creepers and 

 nuthatches frequent the same parts of 

 trees, closely inspecting crevices in the 

 bark, which may yield some insect 

 tidbits. The titmice, chickadees, and 

 kinglets choose for their hunting 

 grounds, the smaller branches, twigs 

 and buds, where may be found the 

 small insects and their eggs of which 

 these little birds are so fond. The 

 cuckoos, orioles, vireos and warblers 

 closely examine the leaves, and prey 

 upon the larvae and sucking insects so 

 abundant there. The humming-birds, 

 with some assistance from other small 

 species, prey upon insects frequenting 

 flowers. Moreover, the birds which 

 feed upon or about trees are not the 

 only ones that benefit them by devour- 

 ing their insect foes. When these 



insects take to flight, they are likely 

 to be snapped up by the flycatchers, 

 and when, as frequently happens, they 

 form large migratory swarms, they are 

 preyed upon voraciously by the night- 

 hawks, swifts, and swallows. 



A large number of birds participate 

 in the destruction of forest insects, and 

 it is fortunate that this is the case, for 

 the insect foes of trees are legion. 

 More than 500 different kinds of insects 

 are known to live upon a single species 

 of tree, and the number of individuals 

 of these pests that are sometimes 

 present is practically infinite. Bark 

 infesting insects are among the most 

 destructive enemies of the forest; they 

 have been known to kill almost every 

 tree of certain species over hundreds of 

 square miles. Wood borers hasten the 

 decay and disintegration of trees and 

 are especially injurious to shade trees; 

 leaf -feeding insects frequently strip trees 

 or make them appear as if scorched by 

 fire, and, in some cases, have threatened 

 to destroy all of the trees upon which 

 they feed over vast areas. The total 

 damage to trees by insect pests is 

 enormous, and several years ago was 

 estimated to exceed $110,000,000 

 annually. Not only is the damage 

 extremely large, but the difficulties of 

 directly combating insect pests in forests 

 are so great that man is able to do 

 comparatively little. The services of 

 natural enemies of the destructive 

 insects should therefore be highly appre- 

 ciated. If they serve to reduce the 

 damage by only a small percentage, 

 the gain to the country is a very large 

 sum. Among these enemies, birds are 

 conspicuous. Their services are well 

 known and have long been acknowl- 



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