THE RUSTY BLACKBIED. 



49 



insects is destroyed and very few useful ones are taken. As rusty 

 blackbirds do not inhabit farms, their economic relations can not be 

 said to be very important; but while not preying directly upon nox- 

 ious insects or weeds which interfere with the cultivation of crops, 

 it is yet possible that they incidentally do considerable good by eating 

 insects. Although their foraging is done mostly in pastures and 

 swamps, yet the insects which they devour count just so much from 

 the sum total, and in the long run the destruction of noxious species 

 is, perhaps, nearly as great a good to the farmer as though they were 

 taken directly from his cultivated fields. 



Grasshoppers and many scarabseid beetles are nuisances, and their 

 destruction is a benefit to agriculture, no matter where they may be 

 found. The same may be said of caterpillars and many other insects, 

 which, though now feeding on useless plants of the marsh or thicket, 

 are liable at any time, through an unusual increase in numbers or a 

 change in environment, to turn their attention to some crop and 

 become a veritable pest. On the other hand, aquatic beetles and small 

 crustaceans, which form a considerable percentage of the diet of the 

 rusty grackles, are to a great extent carnivorous in their habits, and 

 it is difficult to see in what way they can ever become of any great 

 economic importance. 



The following table shows the percentages of the principal elements 

 of the food for each month: 



Food of the rmty blackbird. 



fN UMBER OF STOMACHS EXAMINED: January, 1; February, 6; March, 17; April, 49; May, 7; June, none 

 collected; July, none collected; August, 4; September, 5; October, 25; November, 15; December, 3; 

 total, 132. J 



Predaceous beetles 



May-beetle family 



Other beetles , 



Caterpillars 



Grasshoppers 



Other insects 



Spiders and myriapods . . 



Other animal food 



Total animal food . 



4.0 

 0.2 

 2.5.8 

 0.9 

 1.5 



20.0 

 4.1 

 1.3 



44.3 

 26.0 

 23.0 



2.2 

 3.2 

 1.6 

 2.3 

 44.2 

 4.5 

 2.7 

 5.1 



72.2 



63.0 



65.8 



VEGETABLE. 



Com 



Other grain 



Weed seed 



Other vegetable food 



Total vegetable food 



87.0 

 12.0 

 1.0 



Per- 

 cent. 

 1.7 

 2.0 

 10.1 

 2.5 

 12.0 

 13.7 

 4.0 

 7.0 



53.0 



17.6 

 6.8 

 6.0 



16.6 



3074— No. 13- 



