BIEDS IN" RELATION" TO THE ALFALFA WEEVIL. 25 



The vegetable food, amounting to 22.2 per cent, becomes important 

 in this month, as nearly two-thirds was of grain, mostly wheat, the 

 rest consisting of weeds and rubbish. 



By August most of these blackbirds had forsaken the alfalfa fields 

 and were paying attention to grain. Such animal food as they 

 needed was amply supplied in the season's crop of grasshoppers. 

 Two stomachs secured are too few for accurate deductions, but both 

 contained adult weevils, 25 and 12 respectively averaging 13 per cent 

 of the contents. Grasshoppers made up 38.5 per cent, while the 

 vegetable element, all of which was grain, amounted to 43.5 per cent. 



Field observation and analysis of material collected indicate that 

 the young of Brewer's blackbird hold a very high place among the 

 enemies of the weevil. While the stomach contents may not show so 

 high a percentage as in some other species, the size and voracious 

 nature of the bird means that a large quantity of food is consumed. 

 The other elements of its animal food also are highly in its favor. 



Adults. — In the season of 1912 Brewer's blackbirds did not become 

 abundant before the first of May. Only two adults were secured in 

 April, one of which had eaten a single weevil. The other, taken in 

 a cattle corral during a snow storm, had eaten nothing but grain. 



In May 45 stomachs were collected, some of which contained sur- 

 prisingly large numbers of these insects. Only four of the birds ex- 

 amined had failed to partake of this food, and its bulk amounted to 

 16.85 per cent of the stomach contents. The advancement in the life 

 cycle of the weevil in the season of 1911 over that of 1912 is readily 

 shown by this material. The 11 birds taken in the former year 

 averaged 6.64 adults and 50.09 larvae apiece, while those of 1912 had 

 taken no larvae whatever but had eaten 10.76 breeding adults apiece. 

 A female collected in May, 1911, had eaten 25 adults and 246 larvae, 

 comprising 89 per cent of the food. This same bird also had eaten 

 a grasshopper, a cricket, a caterpillar, and a clover-root curculio 

 {Sitones hispidulus). A male taken in the same month had con- 

 sumed no less than 10 adults and 200 larvae, equaling 97 per cent of 

 the food, while another had eaten 6 adults and 105 larvae. While the 

 material of 1912 did not reveal such large numbers, the work was 

 confined entirely to the destruction of breeding adults. The highest 

 number taken in May of the latter year was 50 adults. One bird had 

 eaten 33, while five others had taken over 20 individuals apiece. 



Caterpillars, with a percentage of 15.67, were the most important 

 of other animal foods. Hemiptera, the greater part of which was the 

 small cicada, Platypedia pwtnami, and carabid beetles, with the 

 genus Amara predominating, composed about 6^ per cent each. 

 Orthoptera, Hymenoptera, and Diptera about equally divided the 

 balance of the animal food. The vegetable contents, amounting to 

 34.11 per cent, was largely grain, much of which doubtless was waste. 



43778°— Bull. 107—14 4 



