330 BULLETIN 19 7, UNITED STATES NATIONAL MUSEUM 



nests by continuing to bring fresh cobweb throughout the course of 

 incubation, vireos apparently never tal^e this precaution. 



The nestlings are clothed with feathers by their tenth day. At the 

 age of from 12 to 14 days, when they can still scarcely fly, they forsake 

 their swinging cradle. They then rather closely resemble their parents 

 in plumage, the chief difference being the absence, in the fledglings, 

 of the darker margins of the gray crown. Their eyes are brown instead 

 of red. 



Food. — In the absence of careful analyses, such as have been made 

 for North American birds, it is only possible to state in general tenns 

 the food of the yellow-green vireo. Probably the bulk is made up of 

 insects, spiders, and larvae, which they hunt among the foliage and 

 on the more slender branches, where they are constantly flitting 

 about, pausing now and again to peer to this side and that. But they 

 eat also many berries, such as those of the Loranthaceae, and various 

 arillate seeds. 



Behavior. — "Wliile I watched the nest attended by the female alone, 

 a second vireo once arrived following close behind her. After de- 

 livering the food she had brought, she flew off ; and then the stranger 

 alighted upon the rim of the nest, looked in, uttered a few low notes, 

 then hurried away in pursuit of her. Soon she returned, gave an 

 insect to one of the nestlings, and settled in the nest to keep them 

 warm. Then the other vireo, who had followed her to the nest, 

 alighted on the supporting branch close beside it and turned to face 

 her. From the color of his eyes, brighter red than those of the female, 

 I took this bird to be a male. Although full grown, the conspicuous 

 yellow corners of his mouth, and his imperfect plumage, revealed liis 

 immaturity. On his perch almost within reach of the nest, he swayed 

 from side to side, voicing the while low, weak notes, and opening wide 

 his mouth, as if begging for food. Then he began to deliver typical 

 vireo song notes, clear but disjointed. The mother seemed to dis- 

 approve and opened her mouth threateningly toward him; but he 

 continued his queer performance for several minutes, until she 

 plucked a seed from the cluster beside the nest and flew away with 

 it, with the young male in close pursuit. 



Voice. — Like the red-eyed vireo, the yellow-green vireo is among 

 the most tireless and persistent of songsters. His song so closely re- 

 sembles that of his relative that without hearing the two within a 

 shorter interval of time than is usually possible it is difficult to say 

 how they differ. Sturgis (1928) states that the yellow-green vireo's 

 song "differs more in tone than character from that of V . olivacea 

 of the United States * * * The brief phrases of which it con- 

 sists, are slighter, sharper pitched and less musical than those of its 

 northern relative." She evidently refers, not to the Central American 



