Cowbird. 145 



bank beyond; but at length darkness reigned over the 

 scene. 



Like their regular associates, the cowbirds manifest their 

 gregarious nature early after the breeding season by form- 

 ing into flocks, the numbers varying from twenty to fifty 

 or sixty. The old birds have then gone through their 

 summer moult, and the glossy black of the males has been 

 changed into the duller colors worn by the females and 

 the young of the year. At this time of the year the cow- 

 birds may be seen in the great flocks of blackbirds of 

 various species assembling here and there, congregating 

 where food is most abundant and easy to be procured. 

 They leave this locality comparatively early, the flocks 

 beginning to form ]ate in June, though the larger flocks 

 are observed in July and early August. Their move- 

 ments to the Southern States (where they spend the win- 

 ter), and their manners while sojourning there, are very 

 similar to those of the other associated species. 



Eobert Eidgway gives their habitat as temperate North 

 America (except Pacific Coast), north to about the sixty- 

 eighth parallel. They breed chiefly north of the thirty- 

 fifth parallel, and w^inter mainly south of the same par- 

 allel, down to the southern borders of the United States. 



It has been generally inferred that the impositions of 

 the cowbird are especially harmful in restricting the num- 

 bers of insectivorous and song birds, but it does not nec- 

 essarily follow that the balance of nature is disturbed by 

 the peculiar habits of this species. Late investigations of 

 the food habits of the cowbird indicate that the species is 

 largely bene'ficial, for Prof. Beal's report read before the 

 Biological Society, D. C, showed the food of the cowbird 

 to consist of " animal and vegetable matter in the pro- 

 portion of about twenty-eight per cent, of the former to 

 seventy-two per cent, of the latter. Spiders and harmful 

 insects compose almost exclusively the animal food, while 

 weed seeds, waste grain, and a few miscellaneous articles 

 make up the vegetable food." It is not improbable that 

 the so-called insectivorous birds displaced by the cowbird 

 are thus kept in check by this natural agent, and their 

 mission performed by the usurper in directions as helpful 

 10 



