AGEL.EUS THILIUS. 97 



interior ; as a rule when they have captured a Lenatero's nest they 

 break a hole in the side and so admit the light and form an easy 

 entrance. One summer a pair of Bay-wings attacked a Lenatero's 

 nest on one of my trees ; the fighting was kept up for three or four 

 days, and then at the foot of the tree I found five young Lenateros, 

 fully fledged, which had been pecked to death and thrown out of the 

 nest. 



The eggs of the Bay-wing are five in number, nearly round, and 

 densely marked with dusky reddish brown. 



Once I observed two young Bay-wings following a Yellow-breast 

 (Pseudoleistes virescens) with their usual peculiar hunger-cry, and 

 while I watched them they were fed several times by their foster- 

 parents. Naturally I concluded that the Bay-winged Cow-bird is 

 sometimes parasitical on other species, but I never saw anything after- 

 wards to confirm me in that belief, and I believe now that I was 

 mistaken, and that the young Bay-wings were not real Bay-wings, 

 but the young of Molothrus rufoaxillaris. 



97. AGEL.EUS THILIUS (Mol.). 

 (YELLOW-SHOULDERED MARSH-BIRD.) 



Agelaeus thilius, Burm. La-Plata Reise, ii. p. 492 (Mendoza, S. Juan, Cata- 

 marca) ; Scl. et Salv. Nomencl. p. 37 j Durnford, Ibis, 1876, p. 159 (Buenos 

 Ayrcs), 1877, p. 33 (Chupat), p. 174 (Buenos Ayres), et 1878, p. 394 

 (Chupat) ; White, P. Z. S. 1882, p. 602 (Buenos Ayres) ; Doring, Exp. al 

 Rio Negro, Zool. p. 40 (Colorado) ; Barrows, Bull. Nutt. Orn. Cl. viii. 

 p. 134 (Entrerios) j Scl. Cat. B. xi. p. 343. 



Description. Black ; lesser upper and under wing-coverts yellow ; bill and 

 feet black : whole length 5'5 inches, wing 3' 6, tail 2'7. Female : above pale 

 brown striated with black ; distinct superciliaries white ; beneath paler, cine- 

 raceous white with black striations ; smaller, and bill shorter. 



Hab. S. Peru, Chili, Paraguay, and Argentina. 



This bird is abundant everywhere on the pampas, and does no 

 migrate, but inhabits marshy situations in summer, building its nest 

 amongst the rushes, and in winter ranges over the country. The male 

 is entirely of an intense black, except the shoulders, which are pure 

 yellow ; the female is dull grey with fuscous markings, and, as was 

 long ago remarked by Azara, the grey-plumaged are very much more 

 numerous than the black individuals. The young birds are like the 

 females, and possibly do not acquire the full black plumage until the 

 second year, which would account for the great number of grey birds. 



These birds are extremely sociable, being seen in flocks all the year 

 VOL, i. H 



