ECONOMIC VALUE 01 BIRDS TO THE STATE. 7 



upon the existence of the other. Birds are not only essential to the welfare of the 

 tree, but the tree is necessary to the life of the bird. Consequently, there has been 

 established what is termed " a balance of life " wherein there is the most delicate 

 adjustment between the tree, the insect, the bird and the sum total of the condi- 

 tions which go to make up their environment. The more trees, the greater the 

 number of insects, and, hence, an increase not only in food supply for the birds, 

 but an increase in the number of nesting-sites. 



Destroy the trees and the insect finds new food in the crops of the farmer, but 

 the birds, although food is still abundant, lose their home when the tree falls, and, 

 lacking the nesting-sites and protection from their enemies once found in its 

 spreading branches, they soon perish. 



What we may call artificial forest conditions are to be found in parks, squares, 

 village streets, and in our gardens. Here forest trees may find a suitable soil, but 

 birds are often less abundant in such localities than in the forest, and consequently 

 the trees growing in them are notably less health)- than forest trees. It is in these 

 semi-domesticated trees that a scourge of injurious insects most often occurs, occa- 

 sionally to be followed by a marked increase of their bird enemies, which are 

 attracted by the unusual abundance of food. Such an instance is recorded in Bird- 

 Lore for October, 1899, by Caroline G. Soule, who writes: 



" Last year, at Brandon, Vermont, the tent-caterpillars were so abundant as to 

 be a serious injury and annoyance. They lay in close rows, making wide bands on 

 the tree trunks. They spun down from the upper branches and fell upon the 

 unfortunate passers-by. They crawled through the grass in such numbers that it 

 seemed to move in a mass as one looked down upon it. Under these circumstances, 

 birds might be expected to do strange things — and they did. 



"The pair of Downy Woodpeckers which lived near us were frequently seen on 

 the ground picking up the crawling tent-caterpillars. They seemed to prefer taking 

 them from the ground to taking them from the trees, though there were more on 

 the tree-trunks than on the ground even. And the Woodpeckers seemed to have 

 no difficulty in moving on the ground, though they moved more slowly than when 

 dodging around a tree. 



" Two mountain-ash trees on the place were infested by borers, though only 

 slightly and only near the ground, and at the foot of one of these trees the Downy 

 Woodpeckers made many a stand, while they probed the borer-holes with their 

 bills. 



" The Cuckoos came boldly into the village and fed and fed, flying about quite 

 openly. The Nuthatches flew to a band of caterpillars on a tree-trunk, and were so 



