24 CIVIC BIOLOGY 



doing for the common good. From an earlier chapter we have 

 learned of the enormous tax which insects impose. The chief 

 economic service of birds consists in the destruction of insect 

 pests, and our national bill of insect damage, $1,049,500,000, 

 may be roughly taken as a measure of our deficiency in bird life. 



Reed estimates that with 5 birds to the acre and 100 

 insects daily per bird, the birds of Massachusetts require for" 

 food each day during five months of the year, 2,560,000,000 

 insects; or, allowing 120,000 insects per bushel, 21,000 bushels. 

 The work of winter birds and migrants, he thinks, amounts to 

 nearly half this number for the colder months, in destruction 

 of hibernating insects and eggs, larvae and pupae. A chickadee 

 has been known to eat from 500 to 4000 eggs in a single day. 



For Nebraska, Professor Lawrence Brunner's estimate is as 

 follows : 



Taking as a basis for our estimations the figures given in my leaflet 

 entitled A Plea for the Protection of Our Birds, we would have about 

 75,000,000 birds, or approximately 35,000,000 to 40,000,000 pairs that 

 nest here (Nebraska). Should each pair of this large number rear four 

 young, there would be required a sufficient food supply for from 140,- 

 000,000 to 160,000,000 young birds. If, as we suggested in that paper, 

 a single bird requires on an average 25 insects per day, the enormous 

 number of 4,000,000,000 insects, or 35,000 bushels of 120,000 insects, 

 would be required each day to feed the young birds alone. But young 

 birds need much more food than do old ones, and we should at least 

 double this quantity for the young birds. Then to this must be added 

 that required by the parent birds themselves while taking care of the 

 young, making a grand total of 86,000 bushels, or 107 carloads of 20 

 tons each, provided we allow 50 pounds as the weight of a bushel. 



Feeding tests and the actual observation of birds from 

 daylight to dark have given us our most valuable data with 

 reference to the destruction of insects by birds. 



A female wood pewee from 4.30 A.M. to 6.52 P.M. was seen to catch 

 568 insects. A brooding bird of the same species from 4.46 A.M. to 6 P.M. 

 caught 208. The first was feeding her nest ; the second merely catch- 

 ing for herself. 



