FAMILY VIREONIDAE 



221 



During the courtship season I have several times observed males 

 posed with head and neck erect, crest raised, and tail stiffly spread. 

 Chasing is also frequent among males. Skutch (Pacific Coast Avif., 

 no. 34, vol. 2, 1960, p. 22) describes a female Yellow-green Vireo tend- 

 ing her nest while courted by an immature male that perched at the edge 

 of the nest, swayed back and forth, and sang. In 1970 Morton found 

 pairs on the Pacific slope of the Canal Zone beginning to nest in mid- 

 January; they fledged young before any birds had even returned to 

 the Caribbean coast, only 54 km away. On the Pacific Coast the last 

 adults with dependent fledged young were seen on July 14. 



The nest is a typical vireo construction. I found one at La Palma, 

 Los Santos, on March 27, 1948, that was hung in a little fork 5 m from 

 the ground. The outside was covered with lichen and spider webs. 

 Skutch (op. ext., p. 15) lists "small papery leaves of bamboo or grass, 

 fibrous roots of epiphytes plucked from slender branches, and much 

 cobweb" as the ingredients. The nest is built entirely by the female. 



The clutch is usually three eggs. Major General G. Ralph Meyer 

 found a nest on May 15, 1941, on the Gamboa Road near the Naval 

 Station in the Canal Zone; the measurements of all eggs were 21x15 

 mm. Peters (op. ext., p. 579) describes eggs of this species from Costa 

 Rica as "white, speckled chiefly at the larger end with spots varying in 

 color from a dark chestnut to an orange rufous, the chestnut pre- 

 dominating." 



Skutch (op. cit.) observed that incubation is performed entirely by 

 the female and requires 13 or 14 days. At hatching the nestlings have 

 a few scattered tufts of very short down and their eyes are tightly 

 closed. They are fed a diet of insects by both parents. By their fourth 

 day pin feathers have begun to push through, but the birds' eyes are 

 still shut. On their eighth day of life the nestlings are feathered ex- 

 cept on the head, and their eyes— brown rather than red — are fully 

 open. At 1 1 days the young are well feathered and move restlessly in 

 the nest, which they will leave within the next 3 days. 



VIREO ALTILOQUUS (Vieillot): Black-whiskered Vireo, Vireo Barbinegro 



Rather small; crown dull gray; rest of upper surface dull olive- 

 green; superciliary whitish; dusky moustachial stripe; undersurface 

 white; undertail coverts pale yellow. 



Description. — Length 126-145 mm. Adult (sexes alike), crown 

 brownish, usually without any dusky border; rest of upper surface 

 dull olive-green; wing coverts, primaries, and secondaries dusky, with 



