FAMILY V1RE0NIDAE 



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men taken September 27, 1927, at Changuinola in the Chiriqui Lagoon 

 region of Bocas del Toro. Loftin (in litt.) reports that in 1962 Yellow- 

 green Vireos were taken rather regularly between September 7 and 

 October 30 in the mist nets operated by the Gorgas Memorial Labora- 

 tory at Almirante, Bocas del Toro; presumably, these were migrants 

 from farther north. 



The Yellow-green Vireo is the only oscine that breeds in Central 

 America and is definitely known to migrate to South America, where it 

 spends a few months in the upper Amazon Basin. Its breeding range 

 extends north to Mexico and southern Texas; undoubtedly the birds 

 mentioned above from the Caribbean slope and also some from higher 

 elevations on the Pacific slope are transients. Yellow-green Vireos 

 usually have passed through or withdrawn from Panama by late Oc- 

 tober, although in 1963 Loftin netted 1 at Ancon, in the Canal Zone, as 

 late as November 17. Although there is some variation from year to 

 year, usually by late December (December 20, 1970, at Fort Kobbe, 

 Canal Zone [Morton, Auk. 1977, p. 99]) the first birds return to the Pa- 

 cific Coast; in mid- January birds returning there are at their peak. 

 Farther inland the peak is slightly later, and on the Caribbean slope it 

 does not occur until mid-March. (In 1962 I observed a considerable 

 flight at El Potrero, Code, as late as March 8, when I saw as many as a 

 dozen birds gathered in one berry-bearing tree at the same time) . Mor- 

 ton (op. cit) suggests that the breeding season is timed to coincide with 

 an abundance of fruit, which is available sooner on the dry Pacific Coast 

 than it is farther inland or on the Caribbean slope. The withdrawal to 

 South America is at a time when fruit is more abundant there than 

 during the late rainy season in Panama. 



H. Loftin's banding data indicate that, despite migration, adults re- 

 turn to the area where banded: 2 banded at Curundu, Pacific slope in 

 the Canal Zone on March 6 and 9, 1963, were recaptured on February 

 9 and 11, 1964, and the former again on April 2, 1966; 1 banded at San 

 Francisco, Veraguas, on April 26, 1965, was recaptured May 5, 1969. 



The taxonomy of the Yellow-green Vireo is disputed. Blake ( Check- 

 list Birds World, vol. 14, 1968, p. 123) treats flavoviridis as a race of 

 Vireo olivaceus, as well as the South American V . chivi complex, al- 

 though they differ in wing- formula and in color and there is no evidence 

 of intergradation. Peters (Auk, 1931, p. 575-587) considered V. flavo- 

 viridis as a full species, with the races insulanus breeding in Panama, 

 nominate flavoviridis on the mainland north of Panama, and forreri 

 breeding in the Tres Marias Islands off the west coast of Mexico, 

 whereas Blake identifies some of the breeding birds of Panama as 



