(YELLOW-SHOULDERED MARSH-BIRD.)
+Agelæus thilius+, _Burm. La-Plata Reise_, ii. p. 492 (Mendoza, S.
Juan, Catamarca); _Scl. et Salv. Nomencl._ p. 37; _Durnford,
Ibis_, 1876, p. 159 (Buenos Ayres), 1877, p. 33 (Chupat), p. 174
(Buenos Ayres), et 1878, p. 394 (Chupat); _White, P. Z. S._ 1882,
p. 602 (Buenos Ayres); _Döring, Exp. al Rio Negro, Zool._ p. 40
(Colorado); _Barrows, Bull. Nutt. Orn. Cl._ viii. p. 134
(Entrerios); _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, cineraceous 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 not 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
round, even during the breeding-season; in winter a great many males
separate themselves from the females, and are found associating together
in flocks of from thirty to forty individuals.
They feed on the ground, keeping to the moist borders of marshes during
summer; they avoid woods, but occasionally alight on trees, where they
all sing in concert. The song, when an individual is heard singing
alone, is, though limited in its range, very sweet, some of the notes
being remarkable for their purity and expression. The bird sits on a
rush or stalk while singing, and makes a long pause after every note or
two, as if to make the most of its limited repertory. There is in the
song one rich full note, which, to my mind, is unequalled for plaintive
sweetness, and I am therefore surprised that Azara says only of this
species that it sings passably well--'_canta razonablemente_.'
The nest is neatly made of dry grasses, and attached to the rushes
growing in the water. The eggs are four, pointed, and spotted at the
larger end with dull brown and black on a white ground.