Their flight is singularly graceful; and during migration the flocks are seen to follow each other in rapid succession, each flock being usually composed of from fifty to a hundred individuals, sometimes of a much larger number. It is most interesting to watch them at such times, now soaring high in the air, displaying the deep chestnut hue of their breasts, then descending with a graceful curve towards the earth, as if to exhibit the dark metallic green and purple reflexions of their upper plumage. The flock is meanwhile continually changing its form or disposition, as if at the signal of a leader. One moment it spreads out in a long straight line; suddenly the birds scatter in disorder, or throw themselves together like a cloud of Starlings; as suddenly they again reform to continue their journey in the figure of a phalanx, half-moon, or triangle. The fanciful notion can scarcely fail to suggest itself to the spectator that the birds go through these unnecessary evolutions intelligently in order to attain a greater proficiency in them by practice, or, perhaps, merely to make a display of their aerial accomplishments. The Glossy Ibis has another remarkable habit when on the wing. At times the flock appears as if suddenly seized with frenzy or panic, every bird rushing wildly away from its fellows, and descending with a violent zigzag flight; in a few moments the mad fit leaves them, they rise again, reassemble in the air, and resume their journey. 328. THERISTICUS CAUDATUS (Bodd.). (BLACK-FACED IBIS.) +Theristicus melanops+, _Darwin, Zool. Beagle_, iii. p. 128 (Patagonia). +Geronticus melanopis+, _Scl. P. Z. S._ 1871, p. 261. +Theristicus melanopis+, _Scl. et Salv. Nomencl._ p. 127; _Durnford, Ibis_, 1877, p. 190 (Buenos Ayres), et 1878, p. 400 (Patagonia); _Barrows, Auk_, 1884, p. 272 (Azul). +Theristicus caudatus+, _Elliot, P. Z. S._ 1877, p. 498. +Ibis albicollis+, _Burm. La-Plata Reise_, ii. p. 510 (Paraná, Mendoza, Tucuman). _Description._--Sides of throat, and lores bare, skin black; top of head and lower part of neck in front reddish chestnut; neck white, a narrow line of feathers running up the centre of the throat to the chin; back and wings greyish brown, with green reflexions, feathers edged with light brown or whitish; tertials and outer webs of secondaries for two thirds of their length white, remainder dark green; primaries dark green; rump and upper tail-coverts light bronzy green; tail dark bronze-green; underparts brownish black, with green reflexions: whole length 33·0 inches, wing 16·25, tail 9·75, bill along culmen 7·0, tarsus 3·5. _Female_ similar. _Hab._ Antarctic South America.