This little bird is rarely met with in the desert pampas, but throughout the settled portion of the Buenos-Ayrean province it is one of the most common species of the _Tyrannidæ_. It arrives from the north in September, and is very regular in its migrations, although apparently a very feeble flier. It frequents open grounds abounding in thistles, tall weeds, or bushes, and is consequently most abundant about houses. It is extremely active, and occasionally darts after a passing insect and captures it on the wing, especially soft insects, like moths and butterflies, to which it is most partial. It subsists principally, however, on small caterpillars and spiders, for which it searches diligently among the leaves, after the manner of the Wren. Although belonging to the songless division of the Passeres, this small Tyrant-bird possesses a formal song, which the male utters with great frequency, the only other member of the Tyrant-family that I am acquainted with which really sings being the Scarlet Tyrant (_Pyrocephalus rubescens_). The music of the Reed-Tyrant is weak but curious; it is composed of five brief percussive notes, distinctly metallic in sound, which may be imitated by gently and slowly striking _fa la mi sol fa_ on the highest keys of the piano. To utter this quaint little song the bird perches itself on the summit of a weed or bush, where it solicits attention with a little chipping prelude, and then jerks its head vigorously with each note, delivering its few drops of sound with all the assurance of a master in the art of melody. In October it builds a deep elaborate nest of fine dry grass, thistle-down, webs, feathers, and other soft materials, usually in the fork of a weed or thistle three or four feet from the ground. It lays four cream-coloured eggs, the colour deepening to grey at the larger end. 142. HABRURA PECTORALIS (Vieill.). (THIN-TAILED TYRANT.) +Pachyrhamphus minimus+, _Gould, Zool. Voy. Beagle_, iii. p. 61, pl. xv. (Monte Video). +Habrura minima+, _Scl. et Salv. Nomencl._ p. 40; _Cab. Journ. f. Orn._ 1878, p. 197 (Cordova); _Scl. P. Z. S._ 1879, p. 460 (Cordova). _Description._--Above sandy brown, with a dark-greyish tinge on the head, which is subcrested and has the vertical feathers white at their bases; lores and eye-region whitish; wings and tail blackish, edged with sandy brown, which forms in some specimens well-marked wing-bands; beneath pale sandy ochraceous, more rufous on the flanks; throat more or less freckled with black; bill and feet dark brown: whole length 4·0 inches, wing 1·9, tail 1·7. _Female_ similar, but without the black markings on the throat. _Hab._ Northern La Plata, Uruguay, Paraguay, Brazil, and British Guiana. Examples of this species were obtained by Dr. Döring near Cordova. 143. CULICIVORA STENURA (Temm.). (NARROW-TAILED TYRANT.) +Culicivora stenura+, _White, P. Z. S._ 1882, p. 605 (Misiones).