CONTROL OF INSECT PESTS McATEE 419 



including the vegetable as well as the animal kingdom. Probably 

 half of the total food of birds in general is of vegetable origin. 

 Again, all sorts of animals from protozoans to mammals are eaten, 

 and insects do not contribute more than their due proportion. In 

 short, we must bear in mind that birds feel no obligation to help us, 

 nor do they, as we might wish, feed exclusively upon insects. These 

 limiting factors understood, we shall be the more able to appreciate 

 the activities of birds at their true worth. 



Despite the adaptive radiation in food habits which birds exhibit, 

 and which leads to more or less specialization in various groups, 

 few kinds are so absolutely bound to peculiar feeding methods that 

 they can not forsake them temporarily when some food becomes 

 available in unusual abundance. For a simply stated illustration 

 of this phenomenon the writer draws on Dr. Isaac P. Trimble, the 

 pioneer economic entomologist of New Jersey, who, in his Treatise 

 on the Insect Enemies of Fruit and Fruit Trees, published in 18G5, 

 wrote : 



On the 5th of May, 1864, I shot seven different birds; they had all been 

 feeding freely on small beetles, and some of them on nothing else. There was 

 a great flight of these small beetles that day; the atmosphere was teeming 

 with them. A few days later, the air was filled with ephemera flies, and the 

 same species of birds were then feeding upon these (p. 113). 



A more elaborate example of the same tendency on the part of 

 birds is Prof. Samuel Aughey's findings during his studies of bird 

 enemies of the Rocky Mountain locust in the sixties and seventies. 

 Tempted by the abundance and accessibility of these insects, birds 

 of every kind flocked to the feast. Land birds and water birds, tree 

 frequenters and plains dwellers, whether normally fish, flesh, seed, 

 or fruit eaters — all, from the diminutive humming bird to the 

 largest hawks, came to feed upon grasshoppers. 



Not only is a further striking instance of this phenomenon re- 

 corded by Dr. S. A. Forbes as a result of his study of birds in relation 

 to cankerworms in Illinois, but the conclusions to be drawn are stated 

 so clearly as to be well worth quoting. Dr. Forbes says : 



Birds of the most varied character and habits, migrant and resident, of all 

 sizes, from the tiny wrea to the bluejay, birds of the forest, garden and meadow, 

 those of arboreal and those of terrestrial habit, were certainly either attracted 

 or detained here by the bountiful supply of insect food, and were feeding freely 

 upon the species most abundant. That 35 per cent of the food of all the birds 

 congregated in this orchard should have consisted of a single species of iasect, 

 is a fact so extraordinary that its meaning can not be mistaken. Whatever 

 power the birds of this vicinity possessed as checks upon destructive irruptions 

 of insect life was being largely exerted here to restore the broken balaiKie 

 of organic nature.^ 



^ Forbes, S. A. : The Regulative Action of Birds upon Insect Oscillations, Bull. 111. ►Stale 

 Laboratory of Natural History, Vol. I, No. 6, May, 1883, pp. 20-21. 



