YELLOW-GREEN VIREO 333 



latest date for the departure of the nestlings is June 23. Thereafter 

 the males rapidly become silent. Farther north, where the climate is 

 drier, they continue to nest through July. Thus I found a nest near 

 Alajuela, Costa Rica (at 3,500 feet elevation), with nestlings on July 

 7; near Colomba, on the Pacific slope of Guatemala at 3,000 feet, one 

 with eggs on July 18, and another with nestlings on the 26th. Here 

 the males sang much during July. I have no evidence as to a second 

 brood, and I doubt very much that in El General the birds raise more 

 than one in a season. 



In September the yellow-green vireos depart for the south. They 

 are now silent; and their withdrawal is an inconspicuous event, in 

 sharp contrast to their song-proclaimed arrival in February. Were it 

 not for the fact that the bird watcher is at this season scanning the 

 treetops for the advent of warblers and other migrants from the 

 north, he would hardly become aware of their departure. My latest 

 dates for this vireo are September 27, 1935 (San IMiguel de Desampar- 

 ados, Costa Eica, 4,500 feet), and September 14, 1936 (El General, 

 3,000 feet). When my thoughts were again directed to the bird by 

 the request to prepare this account, at the end of Septeinber 1942, 1 

 began to search for those that earlier in the year had nested in the 

 trees in front of the house, but in vain, for all had silently departed. 

 Griscom states that in Guatemala they have not been found after 

 October 1. 



[Author's note : Mr. Skutch has asked me to look up the references 

 that I have to certain publications that were not available to him when 

 he wrote the foregoing account. Some of these are rather interesting 

 but, with one exception, there is nothing in them that will add much 

 of sufficient importance to what he has written to warrant quoting 

 from them here. James Lee Peters (1931) has published a compre- 

 hensive paper on the status, distribution, and liabits of this species 

 and its subspecies, to which the reader is referred for details. But 

 the following items should be included here : 



Plumages. — "Juvenile. — No specimens in fresh juvenile plumage 

 seen, but judging from partly moulted juvenals the bird has a plum- 

 age like that of F. oUvaceus, but the lateral underparts with a much 

 more extensive and deeper yellowish wash. 



"Immature. — Acquired by a complete post- juvenile moult involving 

 all tracts except the primaries, secondaries, greater wing coverts and 

 tail. In Guatemala this plumage is complete by the beginning of the 

 third week in August. 



"Adult winter.— Not distinguishable from immature plumage; ac- 

 quired by a complete post-nuptial moult beginning about the middle 

 of July and complete before the first of September. 



