220 BIRDS OF THE REPUBLIC OF PANAMA PART 4 



flavoviridis and included part of the Mexican mainland in the breeding 

 range of forreri. When I was in the Pearl Islands in 1944 the bird was 

 common and I secured a series of 21 skins to check on the question of 

 the supposed form insulanus, described by Bangs (Proc. New Eng- 

 land Zool. Club, vol. 3, 1902, p. 73) from El Rey Island and later con- 

 sidered to be the bird of the Panama mainland also. There is variation 

 in depth of color among these, some being decidedly darker, but this 

 seems to be entirely individual, for which reason insulanus was synony- 

 mized with flavoviridis (Wetmore, Smiths. Misc. Coll., vol. 106, no. 1, 

 1946, p. 54). Migrant individuals of forreri may be recognized by 

 their much larger size, as for example a specimen from Socorre, Rio 

 Sinu, Cordoba, Colombia, taken by Carriker on April 25, 1949 

 (USNM no. 412462). No specimens of this race have yet been iden- 

 tified from Panama, however. 



Morton (op. ext., p. 101) examined the stomach contents of 98 

 Yellow-green Vireos taken in Panama and found that 89 percent of the 

 birds specialized in either fruit or insects, with their stomachs contain- 

 ing 90 percent of one or the other; about half specialized in each, while 

 the remaining 11 percent had stomachs containing equal portions of 

 fruit and insects. Those specializing in insects had a far lower volume 

 of food matter in their stomachs. The birds that filled up on fruit may 

 be ones that learned the location of fruiting trees and visited them re- 

 peatedly, even when the trees were outside of their breeding territory. 

 The plants from which Morton found the vireos taking fruit included, 

 in order of decreasing occurrence in stomachs: Miconia sp., Pitheco- 

 loblum rufescens, Didymopanax morototoni, Pittoniotus tricantha, 

 Guazuma uhnifolia, Lasiacis sorghoidea. Two collected by Strauch 

 (Bull. Brit. Orn. Club, 1977, p. 64) weighed 16.6 and 17.7 g. 



The arrival of the Yellow-green Vireo after its absence in South 

 America is easy to detect, since it is a persistent singer, even through 

 the hottest parts of the day. In tone and method of utterance the notes 

 are like those of the Red-eyed Vireo, but somewhat more leisurely and 

 slightly harsher in sound. Sometimes the phrases are shorter and the 

 pauses in between longer than a Red-eyed Vireo's, and I have also 

 heard the song so harsh that it sounded almost like a House Sparrow's. 

 Morton (op. cit., p. 98) found that after pairing, males sang less per- 

 sistently but gave rapid, songlike phrases when moving toward fe- 

 males, who responded with a harsh chatter. In June and July singing 

 increases somewhat, although often males were in molt and not associ- 

 ating with females. They also give a harsh, nasal nywey (Eisenmann, 

 in Htt. ) . 



