FAMILY ICTERIDAE 



343 



a familiar sight. Like other oropendolas, this is a highly vocal bird. 

 Eisenmanri (Smiths. Misc. Coll., vol. 117, no. 5, 1952, p. 53) lists some 

 of its calls as a "liquid croak, grwackoo, grwackoo, grwak, grwak; 

 often grwackoo alone; also a series of gurgling notes like the sound of 

 dripping water, plup, plup, plup, plup-looupoo; also plup alone." Eisen- 

 mann also reports watching a male giving a liquid song, oo-loo-ooh, tloo, 

 coo-oo, tloo-coo-oo, in late April. Chapman (Bull. Amer. Mus. Nat. 

 Hist., vol. 48, art. 3, 1928, pp. 132-133) lists several other calls. Males 

 also produce a variety of noises with their wings in flight that are part 

 of courtship displays. 



The Chestnut-headed Oropendola feeds high in trees. It often moves 

 in groups to and from the nesting colony, and during the nonbreeding 

 season moves through the forest in noisy flocks. One collected by E. A. 

 Goldman at Cana, Darien, on June 19, 1912, contained acridid frag- 

 ments 38%, elytra of an otiorhynchid 2%, about 550 seeds and 2 other 

 indeterminate 60%. The large mass of seeds was apparently from 

 berries. Leek (Auk, 1974, p. 163) has observed this species feeding on 

 the nectar of the large white flowers of the balsa tree (Ochroma limon- 

 ensis). Two males collected by Strauch (Bull. Brit. Orn. Club, 1977, 

 p. 64) weighed 213.4 and 239.4 g; 2 females weighed 134.2 and 141.3 g. 



At Barro Colorado Island, Canal Zone, where Chapman (op. cit. pp. 

 123-166) investigated the nesting habits of this species in great detail, 

 birds return to a previously used nest tree in late December for brief 

 inspections, and females begin constructing new nests in early Janu- 

 ary. In 1964, at Tacarcuna Village in Darien 1 found a colony on March 

 8 to which pairs came occasionally to inspect and peer into old nests, 

 usually visiting several in turn. By March 12 they came in groups of 

 12 or 15 and there was activity in the nest tree all day, although still 

 no new construction. At Barro Colorado most breeding activity ended 

 by the beginning of the rainy season in May, although a few nests were 

 active into July. The nest tree is always chosen for its situation beyond 

 the reach of most predators. In Darien I found a group of nests swing- 

 ing in a tree over the Rio Imamado and another at Jaque on a tree 

 whose trunk had a large wasps' nest. Usually a colony contains 25 to 

 50 active oropendola nests. The nests rarely survive from year to year 

 in usable condition, so new ones are built each season. They are placed 

 on the outermost twigs that are about the diameter of a pencil in width; 

 most nests are on the leeward side of the tree, to avoid damage from 

 the trade winds that blow during this season. The nests seem to be 

 placed as near to one another as possible. 



Male oropendolas go through a noisy and aggressive courtship peri- 



