1911 Encyclopædia Britannica/Hoactzin
HOACTZIN, or Hoatzin, a bird of tropical South America, thought by Buffon to be that indicated by Hernandez or Fernandez under these names, the Opisthocomus hoazin or O. cristatus of modern ornithologists—a very curious and remarkable form, which has long exercised the ingenuity of classifiers. Placed by Buffon among his “Hoccos” (Curassows), and then by P. L. S. Müller and J. F. Gmelin in the Linnaean genus Phasianus, some of its many peculiarities were recognized by J. K. W. Illiger in 1811 as sufficient to establish it as a distinct genus, Opisthocomus; but various positions were assigned to it by subsequent systematic authors. L’Herminier was the first to give any account of its anatomy (Comptes rendus, 1837, v. 433), and from his time our knowledge of it has been successively increased by Johannes Müller (Ber. Akad. Wissensch. Berlin, 1841, p. 177), Deville (Rev. et mag. de zoologie, 1852, p. 217), Gervais (Castelnau, Expéd. Amérique du Sud, zoologie, anatomie, p. 66), Huxley (Proc. Zool. Society, 1868, p. 304), Perrin (Trans. Zool. Society, ix. p. 353), and A. H. Garrod (Proc. Zool. Society, 1879, p. 109). After a minute description of the skeleton of Opisthocomus, with the especial object of determining its affinities, Huxley declared that it “resembles the ordinary gallinaceous birds and pigeons more than it does any others, and that when it diverges from them it is either sui generis or approaches the Musophagidae.” He accordingly regarded it as the type and sole member of a group, named by him Heteromorphae, which sprang from the great Carinate stem later than the Tinamomorphae, Turnicomorphae, or Charadriomorphae, but before the Peristeromorphae, Pteroclomorphae or Alectoromorphae. This conclusion is substantially the same as that at which A. H. Garrod subsequently arrived after closely examining and dissecting specimens preserved in spirit; but the latter has gone further and endeavoured to trace more particularly the descent of this peculiar form and some others, remarking that the ancestor of Opisthocomus must have left the parent stem very shortly before the true Gallinae first appeared, and at about the same time as the independent pedigree of the Cuculidae and Musophagidae commenced—these two groups being, he believed, very closely related, and Opisthocomus serving to fill the gap between them.
The first thing that strikes the observer of its skeleton is the extraordinary structure of the sternal apparatus, which is wholly unlike that of any other bird known. The keel is only developed on the posterior part of the sternum—the fore part being, as it were, cut away, while the short furcula at its symphysis meets the manubrium, with which it is firmly consolidated by means of a prolonged and straight hypocleidium, and anteriorly ossifies with the coracoids. This unique arrangement seems to be correlated with the enormously capacious crop, which rests upon the furcula and fore part of the sternum, and is also received in a cavity formed on the surface of each of the great pectoral muscles. Furthermore this crop is extremely muscular, so as more to resemble a gizzard, and consists of two portions divided by a partial constriction, after a fashion of which no other example is known among birds. The true gizzard is greatly reduced.
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The hoactzin appears to be about the size of a small pheasant, but is really a much smaller bird. The beak is strong, curiously denticulated along the margin of the maxilla near the base, and is beset by diverging bristles. The eyes, placed in the middle of a patch of bare skin, are furnished with bristly lashes, resembling those of horn-bills and some few other birds. The head bears a long pendant crest of loose yellowish feathers. The body is olive-coloured, varied with white above, and beneath is of a dull bay. The wings are short and rounded. The tail is long and tipped with yellow. The legs are rather short, the feet stout, the tarsi reticulated, and the toes scutellated; the claws long and slightly curved. According to all who have observed the habits of this bird, it lives in bands on the lower trees and bushes bordering the streams and lagoons, feeding on leaves and various wild fruits, especially, says H. W. Bates (Naturalist on the River Amazons, i. 120), those of a species of Psidium, and it is also credited with eating those of an arum (Caladium arborescens), which grows plentifully in its haunts. “Its voice is a harsh, grating hiss,” continues the same traveller, and “it makes the noise when alarmed, all the individuals sibilating as they fly heavily away from tree to tree, when disturbed by passing canoes.” It exhales a very strong odour—wherefore it is known in British Guiana as the “stink-bird”—compared by Bates to “musk combined with wet hides,” and by Deville to that of a cow-house. The species is said to be polygamous; the nest is built on trees, of sticks placed above one another, and softer materials atop. Therein the hen lays her eggs to the number of three or four, of a dull-yellowish white, somewhat profusely marked with reddish blotches and spots, so as to resemble those of some of the Rallidae (Proc. Zool. Society, 1867, pl. xv. fig. 7. p. 164). The young are covered only with very scanty hair, like down, and have well-developed claws on the first and second fingers of the wing, which they use in clambering about the twigs in a quadrupedal manner; if placed in the water they swim and dive well, although the adults seem to be not at all aquatic. (A. N.)