350 ANNUAL REPORT SMITHSONIAN INSTITUTION, 193 



In view of the fact that the subtropical and hence, presumably, 

 more recently evolved oropendolas ^ have a yellow band or marks at 

 the base of the maxilla, it is noteworthy that two young Zarhynolms 

 taken from fallen nests on Barro Colorado, June 26, 1925, and April 

 1, 1927, respectively, and a young female with half-gi'own tail taken 

 in eastern Panama, May 27, all have well-marked yellow, supraloral 

 marks. 



Chiefly for the purpose of affording a basis for comparison of the 

 sexes I append a brief description of Zarhynchus. 



Male. — Head, neck all around, throat and upper breast seal-brown ; upper back 

 and wings glossy black ; lower back and rump and upper tail-coverts chestnut ; 

 tail bright yellow, the two central feathers and outer webs of the outer pair 

 black ; sides seal-brown shading through the flanks and ventral region to chest- 

 nut lower tail-coverts. Feathers at the base of the frontal shield elongate, those 

 in the center of the occiput reaching an average length of 50 mm. and with a 

 basal width of about 2 mm. ; two outer primaries incised or narrowed near their 

 ends ; bill large, heavy, and sharply pointed, the maxiUa expanded over the en- 

 tire forehead as a broad, rounded elevated shield. Length (skin), 350; wing, 

 215; tail, 130; culmen, 68; greatest width of frontal shield, 21 mm. 



Female. — Differs from the male chiefly in her smaller size. The black of the 

 body is less extensive and less glossy but this difference is too slight to be notice- 

 able in life. The bill is much smaller, its frontal development less pronounced, 

 the frontal crest shorter and of fewer feathers ; and the primaries are only 

 slightly incised. In flight, the radiation of the ends of the primaries is less pro- 

 nounced and this character, the absence of sound when flying, and smaller size 

 are the characters which in life distinguish the female from the male. Length 

 (skin), 268; wing, 153; tail, 102; culmen, 51; greatest width of frontal shield, 

 16 mm. 



SEASONAL MOVEMENTS 



In a broad sense Zarhynchus wagleri is a resident, nonmigratory 

 species. Studied locally and intensively, on Barro Colorado, at 

 least, it is nonresident and migratory. It appears at its breeding 

 station with remarkable regularity and at the conclusion of the nest- 

 ing season leaves it. While breeding, all its wants are supplied in 

 the forest near its home; at this time it probably rarely goes more 

 than 400 yards from its nest tree. The extent of its wanderings at 

 other times of the year is unknown, but its appearance within the 

 nesting territory during the nonbreeding season is purely casual. 



While Zarhynchus breeds during the dry season, the date when it 

 begins to nest is not closely dependent on the cessation of rain. There 

 has been much variation in the date on which the wet season may be 

 said to have ended and the dry begun on Barro Colorado during the 

 three years the oropendolas have been under observation, as the ap- 

 pended data from the laboratory rain-gage show. 



As for temperature, it varies so little during the year that it prob- 

 ably plays no part in determining the season when birds nest. 



' Ostinopa alfredi, O. atrocaataneus, O, aincipitaiis. 



