322 BULLETIN 19 7, UNITED STATES NATIONAL MUSEUM 



the birds that nest in this great isthmus are permanent residents. 

 Few kinds indeed can be confidently classified as summer residents, 

 breeding in Central America and passing the nonbreeding season far- 

 ther south. But in the five republics north of Panama (Central Amer- 

 ica in the political rather than the geographical sense) , four species 

 appear to belong in this category. Of these, the yellow-green vireo's 

 claim to this status rests upon the largest mass of evidence. The 

 other three are flycatchers: the sulphur-bellied flycatcher {Myiody- 

 nastes luteiventris) , the noble flycatcher {Mylodynastes inaculatus 

 noMlis), and the striped flycatcher {Legatus alUcollis). It is note- 

 worthy that two of these four birds extend their migrations far north 

 of Central America. Possibly, were bird watchers not so exceedingly 

 few in this area of marvelously varied bird life, other breedhig species 

 would be discovered to have similar migratory habits; possibly, too, 

 more widespread observations would show that some of the four listed 

 do not withdraw as completely as we now believe. Where there are 

 so few students to lend confirmatory evidence, one must make general 

 statements with extreme caution. 



In Central America the yellow-green vireo is a bird of the Pacific 

 lowlands and lower elevations of the interior. In both Costa Eica and 

 Guatemala it is, during the nesting season, widespread and familiar 

 on the Pacific slope and in the central highlands, up to about 5,000 

 feet above sea level. Thence it extends down the Caribbean slope 

 through the cleared agricultural lands, but on this side of the isthmus 

 is very rare below the 1,500-foot contour. During my first three years 

 in Central America, spent largely in the Caribbean lowlands of Pan- 

 ama, Honduras, and Guatemala, I did not form the acquaintance 

 of this vireo ; but when I began to study the birds of the central high- 

 lands and the Pacific slope, I soon became familiar with it. This 

 distribution suggests that, in Costa Eica at least, it was originally 

 a species of the lighter, more open forests of the northern Pacific low- 

 lands, and began to cross the lower passes in the central Cordillera, 

 and invade the Atlantic slope, as heavy primeval forests were replaced 

 by pastures and cultivated fields with scattered trees. 



In its mode of life, as in appearance and voice, the yellow-green 

 vireo is the Central American counterpart of its close relation, the 

 red-eyed vireo of North America. It has the same bright red eye, 

 the same deliberate, untiring song, the same habit of hunting rest- 

 lessly amid the foliage where it is difficult to see, builds its nest accord- 

 ing to the same pattern. It avoids the heavy rain forests, rarely if 

 ever venturing into their sunless depths, and is at home in light second- 

 growth woodland, in orchards, hedgerows, and roadside trees. Shady 

 pastures are a favorite haunt of the bird ; and the coffee plantations, 

 with their glossy-leafed bushes standing in orderly ranks beneath the 

 evenly spaced shade trees, offer conditions greatly to its liking. But 



