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. 98. AGELÆUS FLAVUS (Gm.). (YELLOW-HEADED MARSH-BIRD.) +Xanthosomus flavus+, _Scl. et Salv. P. Z. S._ 1869, p. 632 (Buenos Ayres); _iid. Nomencl._ p. 37; _Durnford, Ibis_, 1878, p. 59 (Buenos Ayres); _Döring, Exp. al Rio Negro, Zool._ p. 41 (Carhué); _Barrows, Bull. Nutt. Orn. Cl._ viii. p. 134 (Entrerios). +Agelæus flavus+, _Scl. Cat. B._ xi. p. 346. _Description._--Black; head and rump, bend of the wing, and body beneath bright yellow; bill and feet black: whole length 6·7 inches, wing 4·2, tail 3·2. _Female_: above brown, slightly striated; eyebrows, rump, and body beneath yellowish; bill and feet brown. _Hab._ Paraguay, Uruguay, and Argentina. Azara called this bird _Cabeza amarilla_, or Yellow-head. It is found throughout the eastern provinces of the Argentine country, ranging south to about the thirty-sixth degree of latitude, and is also common in the Banda Oriental. The dull-plumaged birds are always very much more numerous than the bright-coloured males, though Azara strangely asserts that the sexes are alike. In Buenos Ayres, where it is called "Naranjo" by the country people in allusion to its orange tints, it is very well known on account of its yellow plumage, which looks so wonderfully brilliant in the sunshine, and its partiality for cultivated districts, where it follows the plough to pick up worms, and frequents the orchard to sing, associating with the common Cow-bird and Yellow-breast. It remains all the year, and is very sociable, going in flocks of from twenty to fifty individuals, which when they settle on the trees all sing in concert, pouring out their few peculiar notes with great power and emphasis. Even in the breeding-season these companies do not always break up, and frequently several pairs have nests near together. The nest is usually built in a cardoon thistle, two or three feet above the ground, and is made of dry grass. The eggs are four, pointed, white or with a bluish tinge, and speckled irregularly with deep brown, the spots being closer and sometimes confluent at the broad end.