The Food of Bircls. 151 



In order to determine the number of specimens which it 

 is necessar}^ to examine in each month, to reach reliable 

 averages of benefit and injury, 1 divided my notes on 

 twenty of the specimens for March, into two groups of ten 

 each, so selected that all the localities and all i)arts of the 

 month were equally represented in each group; and then 

 averaged each ten separately and compared the averages. 

 In the first group beneficial insects composed twenty-nine 

 per cent, of the food, and injurious insects fifty-nine per 

 cent. ; in the second group beneficial insects composed 

 twenty-seven per cent, of the food and injurious insects 

 sixty-one per cent. The close correspondence of these av- 

 erages shows that, on this question, ten specimens woukl 

 have given as accurate information as twenty, and indi- 

 cates that ten birds a month will usually afford a fair basis 

 for an opinion. 



April. 



The food for April, as shown by the thirteen specimens 

 of that month (from Normal, Evanston, Waukegan, and 

 Elizabeth, in 1876 and 1880), was remarkable for the num- 

 ber of Aphodii (dung-beetles) it included; twenty-one 

 per cent, of the food of the month was Aphod'uis Ingulna- 

 tus, nine per cent. A. Hmetarlus., and one per cent, unde- 

 termined Aphodii. This peculiarity is accounted for, in 

 harmony with what has l)een said above respecting the 

 feeding habits of the bluebird, by the fact that this is the 

 month when the Aphodii fiy most actively in the latitude 

 of northern Illinois. Carabidft? now stand at eight per 

 cent., including 6'«/'«^w«^«/^/^^/'/5,Pterosticlius,Evarthrus, 

 and other Pterostichi, Platynus, Chlcenius tomentosus^ 

 Anisodactylus rustieus^ Atnphasla infersfilialis, and Har- 

 palus; four percent, of Hemiptera includes Coriscus and 

 Hynienarcys nervosa., while spiders rise to nine per cent. 

 Caterpillars are twenty-one per cent, (seventeen ijer cent. 

 Noctuids), June-beetles (Phyllophaga) two per cent., Cur- 

 culionid^ one per cent., and grasshoppers (Tettigidea sp. 

 and Tettix ornata) eight per cent. ; a total of thirty-two 

 per cent, of injurious insects against twenty-one per cent, 

 of predaceous species. Among the neutral elements we 



