THE FOOD OF BIRDS. 



BY S, A. FORBES. 



Excluding the inhabitants of the great seas, birds are 

 the most abundant of the Vertebrata, occupying in this 

 great subkingdom the same prominent position that in- 

 sects do among invertebrate animals. These two classes 

 thus constitute exceptions to the general rule that the 

 higher and more active animals of each group are the less 

 abundant, — a fact doubtless largely due to the immense 

 advantage given them by their power of flight. It is this 

 which, by making migration possible, enables birds to 

 choose their climates and their seasons, — thus avoiding, in a 

 great measure, one of the most destructive checks upon the 

 multiplication of animals. Their disproportionate number, 

 their universal distribution, the remarkable locomotive 

 power which enables them readily to escape unfavorable 

 conditions, and their immense activity and higher rate of 

 life, requiring for their maintenance an amount of food rela- 

 tively enormous, give to birds in their relation to the pur- 

 suits and interests of man a significance which only here 

 and there one seems ever fully to have realized. A few 

 figures will illustrate and enforce this proposition. 



The careful estimates of three ornithologists and expe- 

 rienced 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 these six months, 

 equally distributed throughout them and equally scattered 

 over the state, we should have three birds on every acre of 

 land. It is my own opinion that about 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 seven thousand two 

 hundred 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. 



