FAMILY ICTKR1DAE 



349 



2 or 3 m above the Rio Mamorri. Very frequently a tree containing a 

 wasp colony is chosen; Cecropias that host stinging ants are sometimes 

 used. At the Barro Colorado colony there were 8 males and 15 females; 

 as in the oropendolas, the females build the nest and raise the young 

 independently. 



The eggs of C. c. vitellinus have not been described, but those of the 

 nominate race in Venezuela are "white with a faint bluish wash, marked 

 with specks, spots and blotches of chestnut over vinaceous brown" 

 (Cherrie, op. cit., p. 205) ; in Venezuela the clutch consists of two eggs. 

 The incubation period is 16 days (Smith, Nature, vol. 219, 1968, p. 

 692) . The first eggs at Skutch's colony hatched on May 12; 3 days later 

 over half the nests had young. The colony, however, was pillaged by a 

 snake (Spilotes pullatus), which destroyed the contents of all but 2 

 nests. Less severe nuisances endured by the colony were the parasitic 

 Giant Cowbird (Scaphidura oryzivora) , although Skutch never saw 

 one actually entering a nest, and the -Piratic Flycatcher (Legatus leu- 

 cophaius), which harassed the caciques but never took over one of their 

 nests. 



CACICUS UROPYGIALIS (Lafresnaye) : Scarlet-rumped Cacique, 

 Charro de Rabadilla Escarlata 



Cassicus uropygialis Lafresnaye, 1843, Rev. Zool. [Paris], 6, p. 290. ("Bogota," 

 Colombia.) 



Medium size; all black with scarlet rump. 



Description. — Length 200-235 mm. Adult (sexes alike), all black, 

 with scarlet rump and lower back. 



Juvenile, like adult, but red rump duller, brownish orange. 



These are forest birds, found in pairs or groups of half a dozen or 

 more, that range mainly through the higher branches. Skutch, who has 

 observed them in Costa Rica (Pub. Nutt. Orn. Club no. 10, 1972, pp. 

 173-181 ) noted that there they were often loosely associated with other 

 treetop birds, including oropendolas, Black-faced Grosbeaks (Caryo- 

 thraustes poliogaster) , Purple-throated Fruitcrows (Querula purpur- 

 ata) , and White-fronted Nunbirds (Monasa morphoeus) . Much of 

 their movement is behind leaf cover, so that often it is not easy to dis- 

 tinguish them from related species of caciques. The light-colored bill 

 is usually prominent, but aside from this they appear plain black, as the 

 red of the lower back is ordinarily covered by the wings. They often 

 whistle musically as they move about, and display considerable curio- 

 sity. At any unusual circumstance they may come with flitting wings 

 and jerking tails to call and scold vociferously near at hand. They feed 



