The Food of Birds. 145 



for eighty-five birds and eighty-three parts for ninety-two 

 birds. It is not until we reach the last two migrants that 

 we find any exception to these results ; and of these, as 

 already said, probal^ly too few have been examined, even 

 yet, to justify settled conclusions. 



Finally, we must consider the family as a unit, must 

 discuss the actual effect of the thrushes as a group upon 

 the plants and animals of the state. A determination of 

 this interesting question involves three elements; the av- 

 erage character of the food of each species as shown by 

 the preceding calculations, the comparative abundance of 

 the species, and the length of its stay in Illinois. I find 

 the estimates of the second of these elements, as made by 

 various collectors, to ditier rather widely; and on this ac- 

 count only an approximate conclusion can be reached. 

 Using the figures most satisfactory to myself, I present 

 the following as a tolerably fair statement of the general 

 food of the family : Sixty-one per cent, of the food con- 

 sists of insects, one per cent, of spiders, two per cent, of 

 Myriapods, and thirty-two per cent, of fruits, eleven per 

 cent, being blackberries, eight per cent, cherries, one per 

 cent, currants and five per cent, grapes. The fragments of 

 grain eaten by the brown thrush will amount to four per 

 cent, of the food of the family, and ants compose eight per 

 cent. Lepido'ptera, Diptera and Ooleoptera are eaten in 

 about equal ratios, the first forming thirteen, the second 

 eleven and the third twelve per cent, of the entire food. 

 Carabidae amount to five per cent., June-beetles to four 

 per cent., wireworms to two per cent, and snout-beetles to 

 two per cent. Hemiptera stand at three per cent., about 

 two-thirds of them predaceous, and Orthoptera at four per 

 cent. Five per cent, of the food was recognized as cut- 

 worms. More briefly, thirty parts of the food consist of 

 injurious insects, including the larva of Bibio, and eight 

 parts of beneficial species, while twenty-six parts consist 

 of edible fruits ; or we may say that injurious insects com- 

 pose about one-third, the edible fruits about one-fourth 

 and the beneficial insects about one-twelfth of the food of 

 the family, the remaining elements being of neutral value. 



