The Food of Birds. 
145 
eight parts for thirty-nine and eighty-six birds respective- 
ly, and the catbird and wood thrush give seventy parts 
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, probably 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 differ 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. Lepicloptera, Diptera and Coleoptera are eaten 
in about equal ratios, the first forming thirteen, the sec- 
ond 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 Orthop- 
tera at four per cent. Five per cent, of the food was 
recognized as cutworms. More briefly, thirty parts of 
the food consist of injurious insects, including the larvae 
of Bibio, and eight parts of beneficial species, while twen- 
ty-six parts consist of edible fruits ; or we may say that 
injurious insects compose 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. 
