4 The Regulative Action of Birds upon Insect Oscillations. 



of those species which, for any reason, became superabundant for a 

 time ? 



For the purpose of answering these questions, two separate 

 lines of investigation are necessary. For the first two we require 

 a knowledge of the food habits of the various species of birds 

 under ordinary circumstances, when the conditions of life are of 

 average character, and especially when no species of insects are 

 unusually and excessively abundant. On the other hand, for an 

 answer to the third question we must look to the food habits of the 

 birds under extraordinary circumstances, where the opposite 

 condition of affairs prevails. We must learn to what extent birds 

 depart from their usual practices when confronted by an uprising 

 of some insect species. If they concentrate for its suppression, 

 they must assist more or less effectively to reduce to order the 

 disturbed balance of life; but if they remain indifferent to this 

 condition of things, their influence is nil. 



The present paper is a contribution to a discussion of the last 

 of the above questions. As a striking and conclusive example of 

 an extraordinary condition of insect life, and of the food of birds 

 in the presence of a disturbed balance of nature, I selected an 

 orchard which had been for some years badly infested by canker- 

 worms, shot a considerable number of birds therein for two suc- 

 cessive years, representing nearly all the kinds seen in the orchard, 

 made full notes of the relative abundance of the species, exam- 

 ined carefully the contents of all the stomachs obtained, with 

 reference not only to the presence of canker-worms but of all 

 other insects as well, and tabulated the results as the basis of this 

 paper. Besides preparing as full an account of the food of these 

 birds as practicable, I have brought the summaries on these tables 

 into comparison with those derived from birds of the same species 

 shot in ordinary situations during the same month. These com- 

 parisons have been confined to a few of the kinds obtained in 

 the orchard, for the reason that most were not found there in suf- 

 ficient number to give a fair idea of the average food of the 

 species. The collections were made in an orchard of forty-five 

 acres of bearing apple-trees ( belonging to Mr. J. W. Robison ) 

 in Tazewell County, 111., which had been infested by canker-worms 

 for about six years. As a result of their depredations, a consider- 

 able part of the orchard had the appearance, from a little distance, 



