BIRDS IN RELATION TO THE ALFALFA WEEVIL. 17 



YELLOW-HEADED BLACKBIRD. 



( Xanthocephalus xanthocephalus. ) 



The yellow-headed blackbird, or soldier bird, as he is more fre- 

 quently called in the West, is the last of the three blackbirds to arrive 

 in large numbers, although a few individuals are said to remain 

 throughout the winter in favorable localities. 



Nestling and juvenile birds. As weevil enemies young yellow- 

 heads do not rank as high as the nestlings of the other blackbirds. 

 The insect amounted to 4.27 per cent of the stomach contents and 

 occurred in 40 of 68 birds collected in June. Larvae were preferred 

 to adults, being taken on an average of 4.13 per bird, as compared 

 with 0.74 for the latter. One nestling 4 or 5 days old had destroyed 

 48 larvae, and a brood of three had eaten, respectively, 42, 25, and 40. 



The work of a colony of about 15 or 20 yellow-heads upon an 

 alfalfa field of three or four acres came under the writer's observa- 

 tion. The breeding marsh was fully half a mile from the source of 

 food supply, and the flight of the parent birds to and from their 

 nests was observed for about a half hour, during which the adults 

 made visits to the fields at the rate of about one every minute. 



Other animal food of the young, strongly indicative of the aquatic 

 environment in which the bird lives, was dragonflies and their 

 nymphs, which formed 43.86 per cent of the stomach contents, and 

 occurred in all but 10 of the 68 stomachs. Some stomachs contained 

 fragments of adult Odonata, which testifies to the ability of these 

 birds to capture insects generally supposed to be effectively protected 

 by their powers of flight. Caterpillars formed about a fourth 

 (24.08 per cent) of the food. Ground beetles (5.7 per cent) , spiders 

 (5.54), grasshoppers (4.09), snails (3.76), and Hymenoptera (2.1) 

 were the principal other ingredients of the animal food. The vege- 

 table portion (2.13) was mainly rubbish. 



Two juvenile birds collected in July had eaten the weevil, one of 

 which had taken 2 adults and 30 larvae. 



Adults. During April and May only two adult yellow -heads were 

 collected each month, a too limited number to allow definite conclu- 

 sions, but it shows that the birds were already preying upon the 

 insect. One collected on the 23d of April had eaten a single adult, 

 while the bulk of the stomach contents consisted of caterpillars. This 

 latter element also composed 97 per cent of the food of the other 

 April bird. The two birds taken in May had fed upon the insect, 

 having eaten three and seven adults, respectively, which averaged 

 10 per cent of their food. 



Of 21 stomachs collected in June only 4 failed to contain the 

 weevil. The insect formed 43.48 per cent of the yellow-head's food 

 and was taken at an average of more than 6 adults and 47 larvae per 

 43778 Bull. 10714 3 



