I20 TR.VNSACTIONS OF THE ILLINOIS 



on. And perhaps I am about as near right as those philosophers who are 

 so anxious to find nothing there. 



An electric or galvanic stream may be extended to an indefinite 

 distance by means of contiguous links. Let us imagine the life of a 

 species to be a single stream of vital force proceeding from the great 

 battery in the hands of Him who sits in the heavens, running through a 

 chain of links which it forms as it proceeds, to cease whenever its con- 

 nection with its source is cut, and we shall at least have a noble concep- 

 tion of life, whether considered scientific or not. 



At the close of the reading the Professor was heartily cheered by the 

 Society and the audience. 



REPORT UPON ORNITHOLOGY. 



Prof, S. A. Forbes, of the Slate Normal University, reported from 

 the Committee on Ornithology as follows : 



THE FOOD OF BIRDS. 



BY S. A. FORBES, DIRECTOR ILL. STATE LAB. OF NAT. HIST. 

 THE THRUSH FAMILY [TurcUdcB). 



In presenting to you another report on the subject which it has now 

 been made my official duty to investigate, I do it with an increased sense 

 of the magnitude and difficulty of the research, and also as an incentive, 

 with a more positive conviction of its importance. 



I wish first to dispose of the question by which one pursuing such 

 work is most commonly confronted, viz.: How is it going to pay? 



The careful estimates of three ornithologists and experienced 

 collectors give, as an average of the whole bird-life of Illinois, three birds 

 per acre during the six summer months. That is to say, if all the birds of 

 the year, except the swimmers, were concentrated in the six months, 

 equally distributed throughout them and equally scattered over the State, 

 we would have three birds on every acre of land. It is my own opinion 

 that at least two-thirds of the food of birds consists of insects, and that 

 this insect-food will average, at the lowest reasonable estimate, twenty 

 insects or insects' eggs per day for each individual of these two-thirds, 

 giving a total for the year of 7,200 per acre, or two hundred and fifty 

 billions for the State — a number which, placed one to each square inch 

 of surface, would cover an area of forty thousand acres. 



Careful estimates of the average number of insects per square yard 

 in this State give us at farthest ten thousand per acre for our whole area. 

 On this basis, if the operations of the birds were to be suspended, the 

 rate of increase of these insect hosts would be accelerated about seventy 

 per cent., and their numbers, instead of remaining year by year at the 

 present average figure, would be increased over two-thirds each year. 

 Any one familiar with geometrical ratios will understand the inevitable 

 result : In the second year we should find these pests nearly three times 



