24 FOOD OF WARBLERS 



ural, and organic nature has a chance to adjust her balances with- 

 out much human interference. 



Warblers are among the most useful birds of the woods, for to 

 them mainly is given the care of the foliage. Trees cannot live 

 without leaves. Lepidopterous larvae, commonly called caterpillars, 

 are among the greatest of leaf-destroyers. They form a great 

 part of the food of Warblers and are fed very largely to their 

 young. 



As the spring waxes warm and merges into summer, the open- 

 ing buds and growing leaves are attacked by a succession of cater- 

 pillars of different species, which, were they not checked by birds, 

 would soon strip all trees of their foliage and keep them stripped 

 throughout the season. Trees breathe through their leaves and, 

 lacking them for a considerable period, they must die. Coniferous 

 trees are killed by a single defoliation. Deciduous trees last 

 longer but the end is sure. 



Warblers save the leaves by constantly pursuing and killing 

 caterpillars. While living in the woods year after year I have been 

 greatly impressed by the vast annual uprising of these pests and 

 the strong repressive influence exerted by the Warblers upon 

 their increase. Each brood of hundreds of caterpillars that hatches 

 from the hidden egg-cluster is soon so reduced in number that very 

 few live to maturity and, even though the survivors may riddle 

 many leaves, the trees remain practically uninjured and the woods 

 maintain their luxuriant summer verdure. 



Thus the presence of Warblers in woodlands goes far towards 

 preserving the trees for their owner. Even should the caterpillars 

 stop short of killing the defoliated trees, the lumberman would 

 still owe to the birds such profit as accrues from woodlands, for 

 without their aid the trees would be so reduced in growth that they 

 would yield no profit. While a tree is stripped of its leaves it 

 makes no wood growth. The wood-ring for that year is smaller 

 than usual, and the annual profit on the tree is proportionately 

 decreased. 



Warblers never receive credit for the good they do, because 

 the insects that they eat are mainly of small size, and the majority 

 of larger species eaten by them are taken in infancy and before 

 they have had a chance to work noticeable injury. Warblers 

 destroy many of the young larvae of such great and destructive 

 insects as the Cecropia and Polyphemus moths while these insects 

 are still too small to attract attention. These larvae which were so 



