YELLOW-THROATED VIREO 287 



where it is now a rare bird." And more recently Bagg and Eliot ( 1937) 

 write : "In the early years of this century, the shade trees it so loved 

 were persistently sprayed with poison for the elm beetle, gypsy moth, 

 etc. Many Vireo-nests were ruined and many Yellow-breasts died from 

 eating poisoned larvas. The bird became uncommon and has remained 

 local." It is hard to believe, and impossible to prove, that the birds, 

 once so common here, have all perished from eating poisoned larvae; 

 it seems likely that some have been forced to look elsewhere for their 

 accustomed food, which they fail to find in tlieir former foraging 

 grounds ; however, there are plenty of unsprayed trees, teeming with 

 caterpillars and beetles, in all of our towns; but tlie vireos do not seem 

 to have found them. There is some other reason, which we do not 

 understand, that has caused the loss of this beautiful vireo. 



Dr. Friedmann (1929) had reports of some 50 cases, from a number 

 of different States, in which the yellow-throated vireo had been 

 imposed upon by cowbirds, and says that the vireo occasionally buries 

 the cowbird's eggs in the lining of the nest, if it has no eggs of its own 

 at the time. Edward K. Ford writes to me from Michigan : "I am 

 reasonably certain that nests started after the first week in June were 

 those of birds whose first attempt was unsuccessful, and that failure in 

 the first instance was due to the cowbird. Of five successful nests, the 

 last feeding of the young in the nest was observed May 31, June 8, July 

 15, July 23, and August 10, respectively. It w^ill be noted that in three 

 cases success was attained after the end of the cowbird's laying cycle 

 which, here, seems to be about July 1. The two low nests mentioned 

 above were parasitized. One of these was deserted after two cowbird's 

 eggs had been removed; the other after the intrusion of two cowbird's 

 eggs and the ejection of one of the eggs of the vireo." 



Harold S. Peters (1936) mentions two external parasites, a louse, 

 Myrsidea incerta (Kellogg), and a mite, Megninia tyr^elli (Haller), 

 that have been found on this vireo. 



Fall. — During the fall migration yellow-throated vireos wander 

 about quite extensively and are likely to be seen almost anywhere that 

 there are trees and in many places where they were not to be found 

 during the breeding season. They sing more or less in September 

 and are then more in evidence than the silent migrants. Their migra- 

 tion is evidently leisurely, for though most of them leave New Eng- 

 land in September or earlier, Mr. Skutch tells me that he has not seen 

 them in Costa Rica before October 20. Mr. Forbush (1929) says: 

 "Wlien the single brood has been raised the parents take them to the 

 berry pastures and they pass the molting season amid the fruiting 

 thickets and are ready for their long southward journey by Sep- 

 tember, if not before." 



Winter. — Mr. Skutch writes to me : "The yellow-throated vireo win- 

 ters throughout the length of Central America, from Guatemala to 



