While flying this species continually utters sharp twitterings and grinding and squealing notes of various lengths.
[29.] TACHYCINETA LEUCORRHOA (Vieill.).
(WHITE-RUMPED SWALLOW.)
Hirundo leucorrhoa, Hudson, P. Z. S. 1872, pp. 606, 845 (Buenos Ayres); Scl. et Salv. Nomencl. p. 14; Durnford, Ibis, 1877, p. 32 (Chupat), 1878, p. 392 (Central Patagonia); White, P. Z. S. 1882, p. 596 (Corrientes); Barrows, Bull. Nutt. Orn. Cl. viii. p. 89 (Concepcion). Cotyle leucorrhoea, Burm. La-Plata Reise, ii. p. 478 (Paraná). Tachycineta leucorrhous, Sharpe, Cat. B. x. p. 114.
Description.—Above glossy dark green; rump white; quills black, washed with green; upper tail-coverts dark green; tail-feathers black with greenish gloss; base of forehead white, extending a little backward over the lores; cheeks and whole under surface white; flanks and sides washed with smoky brown; axillaries and under tail-coverts pale smoky brown; bill and feet black: total length 5·5 inches, wing 4·45, tail 2·0. Female similar.
Hab. Brazil, Paraguay, and Argentina.
This is the most abundant and best known of our Swallows; a pretty bird in its glossy coat of deep green, and rump and under surface snowy white; exceedingly restless in its disposition, quick and graceful in its motions; social, quarrelsome, garrulous, with a not unmusical song, beginning with long, soft, tremulous notes, followed by others shorter and more hurried, and sinking to a murmur. They are the last of all our migrants to leave us in autumn, and invariably reappear in small numbers about the houses on every warm day in winter. Probably many individuals in Buenos Ayres remain through the winter in sheltered situations, to scatter over the surrounding country whenever there comes a warm bright day. I once saw three together, skimming over the plains, on one of the coldest days I ever experienced on the pampas, the thermometer having stood at 29° Fahr. that morning.
Further south their migration is more strict; and on the Rio Negro, in Patagonia, from March to August I did not meet with a single individual. In Buenos Ayres the autumnal migration of the Hirundines begins about the middle of February, and from that date vast numbers of this Swallow are seen travelling north, and, in some seasons, they continue passing for over a month. One autumn, in April, several days after the Swallows had all disappeared, flocks of the Common Swallow began again to appear flying north, and for ten days afterwards they continued to pass in large numbers. They would stoop to dip themselves in a pool where I observed them, and then alight on the reeds and bushes to rest, and appeared quite tired with their journey, rising reluctantly when approached, and some allowing me to stand almost within arm’s length of them without stirring. I had never before observed any later or supplementary migration like this; for, as a rule, the causes which in some years delay the departure of birds seems to affect them all alike. Possibly these late birds come from some remote district, where exceptionally cold weather had retarded breeding-operations.
The White-rumped Swallow sometimes lays in a tree, in the large nest, previously abandoned, of the Leñatero (Anumbius acuticaudatus). Its favourite site is, however, a hole in a wall, sheltered by the overhanging tiles or thatch; for though it does not go much into towns, as Azara has remarked, it is very domestic, and there is not a house on the pampas, however humble it be, but some of these birds are about it, sportively skimming above the roof, or curiously peering under the eaves, and incessantly uttering their gurgling happy notes.
For a period of a month to six weeks before building begins they seem to be holding an incessant dispute, reminding one in their scolding tones of a colony of contentious English House-Sparrows, only the Swallow has a softer, more varied voice, and frequently, even when hotly quarrelling, he pauses to warble out his pretty little song, with its sound like running water. However many eligible chinks and holes there may be, the contention is always just as great amongst them, and is doubtless referable to opposing claims to the best places. The excited twittering, the incessant striving of two birds to alight on the same square inch of wall, the perpetual chases they lead each other round and round the house, always ending exactly where they began, tell of clashing interests and of great unreasonableness on the part of some amongst them. By-and-by the quarrel assumes a more serious aspect; friends and neighbours have apparently intervened in vain; all the arguments of which Swallows are capable have been exhausted, and, a compromise of claims being more impossible than ever, fighting begins. Most vindictively do the little things clutch each other and fall to the earth twenty times an hour, where they often remain struggling for a long time, heedless of the screams of alarm their fellows set up above them; for often, while they thus lie on the ground punishing each other, they fall an easy prey to some wily pussy who has made herself acquainted with their habits.