16 BULLETIN 107, U. S. DEPARTMENT OF AGRICULTURE. 



little to fear from this bird, but the fact that in its egg-laying habits 

 it is parasitic, and frequently so on highly valuable species, has so 

 complicated matters that its exact relation to agriculture is not yet 

 thoroughly understood. In spring and summer the cowbird may be 

 found usually in numbers of from two to six associated with one or 

 more of its relatives in the vicinity of pastures or alfalfa fields. The 

 cowbird's exceptional record as a weevil destroyer does much toward 

 redeeming it for misdemeanors arising from its parasitism. Of the 

 15 birds collected only 1 had failed to feed on the insect. 



Three cowbirds taken in May had eaten the weevil to the extent of 

 over 60 per cent of their food. In one case it amounted to 95 per 

 cent and was present at an average of about 7 adults and 30 larvae 

 per bird. Dung beetles (Aphodius] formed the bulk of the remain- 

 ing animal food. Wheat, which was present in two stomachs, was 

 estimated to be a fourth of the monthly sustenance. 



Ten birds collected in June showed a continuation of the good work 

 started in the preceding month. The only bird failing to eat the 

 weevil was one which had taken three or four nymphs and one adult 

 of the small cicada (Platypedia putnami), which formed nearly the 

 entire stomach contents. The weevil, constituting 42.3 per cent of 

 the food, was taken at an average of 6 adults, 1.4 pupae, and 30.3 

 larvae per bird. The largest number recorded for the species was 

 80 larvae, 3 pupae, and 3 adults, forming 80 per cent of the food. Of 

 the remaining animal food Hemiptera was the most prominent item 

 (18.7 per cent), and was composed of about equal parts of cicadas 

 (Platypedia) and tree hoppers (Membracidae). The vegetable 

 food (27 per cent) was composed largely (18.3 per cent) of the seeds 

 of weeds, among which were filaree, wild mustard, brome grass, and 

 barnyard grass. 



Two cowbirds taken in July had fed on the weevil, adults of the 

 same year's brood in each case, to the amount of nearly 30 per cent 

 of the stomach contents. The remains of a much-digested lepidop- 

 teran comprised about half of the food of one, and a mass of seeds of 

 filaree, amaranth, smart weed, and sunflower formed about 80 per 

 cent of the contents of the other stomach. 



Summary. The food habits of the cowbird in Utah during spring 

 and summer appear to be above reproach. Grain forms but a small 

 portion of its diet, while the alfalfa weevil is by far the largest 

 ingredient of the animal portion. From the first of May to the 

 middle of July the weevil forms over half the animal food, and 

 much of the vegetable portion is composed of weed seeds. In recog- 

 nition of the cowbird's work as a weevil enemy, it would appear that 

 when every suppressive agency must be carefully conserved, the bird 

 should be allowed to continue its good work unmolested by sportsman 

 or small boy. 



