Part 13

In the competition for place, the struggle for its existence, said with reason to be most deadly between such species as are most nearly allied, the operations are imperceptible, and the changes are so gradual, that the diminution and filial disappearance of one species is never attributed to a corresponding increase in another more favoured species over the same region. It is not as if the regnant species had invaded and seized on the province of another, but appears rather as if they had quietly entered on the possession of an inheritance that was theirs by right. Mighty as are the results worked out by such a process, it is only by a somewhat strained metaphor that it can be called a _struggle_. But even when the war is open and declared, as between a raptorial species and its victims, the former is manifestly driven by necessity. And in this case the species preyed on are endowed with peculiar sagacity to escape its persecutions; so that the war is not one of extermination, but, as in a border war, the invader is satisfied with carrying off the weak and unwary stragglers. Thus the open, declared enmity is in reality beneficial to a species; for it is sure to cut off all such individuals as might cause its degeneration. But we can conceive no necessity for such a fatal instinct as that of the Cuckoo and Cow-bird destructive to such myriads of lives in their beginning. And inasmuch as their preservation is inimical to the species on which they are parasitical, there must also here be a struggle. But what kind of struggle? Not as in other species, where one perishes in the combat that gives greater strength to the victor, but an anomalous struggle in which one of the combatants has made his adversary turn his weapons against himself, and so seems to have an infinite advantage. It is impossible for him to suffer defeat; and yet, to follow out the metaphor, he has so wormed about and interlaced himself with his opponent that as soon as he succeeds in overcoming him he also must inevitably perish. Such a result is perhaps impossible, as there are so many causes operating to check the undue increase of any one species: consequently the struggle, unequal as it appears, must continue for ever. Thus, in whatever way we view the parasitical habit, it appears cruel, treacherous, and vicious in the highest degree. But should we attempt to mentally create a perfect parasitical instinct (that is, one that would be thoroughly efficient with the least possible prejudice to or injustice towards another species; for the preservation of the species on which the parasite is dependent is necessary to its own) by combining in imagination all known parasitical habits, eliminating every offensive quality or circumstance, and attributing such others in their place as we should think fit, our conception would probably still fall short in simplicity, beauty, and completeness of the actual instinct of _M. rufoaxillaris_. Instead of laying its eggs promiscuously in every receptacle that offers, it selects the nest of a single species; so that its selective instinct is related to the adaptive resemblance in its eggs and young to those of the species on which it is parasitical. Such an adaptive resemblance could not of course exist if it laid its eggs in the nests of more than one species, and it is certainly a circumstance eminently favourable to preservation. Then, there not being any such incongruity and unfitness as we find in nests into which other parasites intrude, there is no reason here to regard the foster-parents' affection as blind and stupid; the similarity being close enough to baffle the keenest sagacity. Nor can the instinct here appear in the light of an outrage on the maternal affection; for the young _M. rufoaxillaris_ possesses no advantage over its foster-brothers. It is not endowed with greater strength and voracity to monopolize the attentions of the foster-parent or to eject the real offspring; but being in every particular precisely like them, it has only an equal chance of being preserved. To this wonderful parasitical instinct we may well apply Darwin's words, when speaking of the architecture of the hive-bee:--"Beyond this stage of perfection natural selection could not lead."

96. MOLOTHRUS BADIUS, Vieill.

(BAY-WINGED COW-BIRD.)

[Plate VI. Fig. 1.]

+Molothrus badius+, _Burm. La-Plata Reise_, ii. p. 495 (Paraná and Tucuman). _Scl. et Salv. Nomencl._ p. 37; _Hudson, P. Z. S._ 1874, p. 163 (Buenos Ayres); _Durnford, Ibis_, 1877, p. 174 (Buenos Ayres); _Scl. Cat. B._ xi. p. 338.

_Description._--Dull grey, beneath rather paler; wings chestnut; tips of primaries, inner portions of secondaries, and tail blackish; bill and feet black: total length 7·6 inches, wing 3·5, tail 3·0. _Female_ similar.

_Hab._ Argentina, Paraguay, and Bolivia.

In this species the sexes are alike; the plumage of the body is grey-drab colour, with a black spot between the eye and beak; tail dark, the quills cinnamon-colour; beak and legs black. Azara describing it under the name of _Tordo pardo roxiso_, says it is a rare bird, so that it has probably greatly increased since his time, as it is now quite common in the Plata district.

The Bay-wings usually go in small flocks, numbering from ten to thirty individuals, and are not migratory, but in winter they travel about a great deal from place to place without extending their journeys more than a few miles in any direction. They are fond of coming about houses, and are frequently seen pecking at the fresh meat hanging out of doors; and, like other birds of the same tribe, feed chiefly on the ground. They spend a great portion of their time on trees, are familiar with man and inactive, and in their motions singularly slow and deliberate. Their language is varied. Curiosity or alarm is expressed by trilling notes, and before quitting a tree all the birds of a flock ceremoniously invite each other to fly with long clear notes, powerful enough to be heard a quarter of a mile away.

They also sing a great deal in all seasons, the song being composed of soft, clear, rather sweet notes, variously modulated, uttered in a leisurely manner, and seeming to express a composed frame of mind, all the birds in a flock singing in concert. During the cold season the flock always finds some sheltered sunny spot on the north side of a woodpile or hedge, where they spend several hours every day, sitting still and singing in their usual quiet, soft style.

Their extreme sociability affects their breeding-habits, for sometimes the flock does not break up in spring, and several females lay in one nest together; but whether the birds are paired or practice a promiscuous intercourse, I have not been able to discover. They have a great partiality for the large domed nests made by the _Anumbius acuticaudatus_, called Leñatero in the vernacular. One summer a flock of about ten Bay-wings took possession of a Leñatero's nest on one of my trees, and after a few days I took fourteen eggs from it. Though the birds hopped, chirping round me, manifesting great solicitude, the eggs were quite cold, and had I left them many more would have been laid, no doubt; but as they were piled up three or four deep in the nest they could never have been hatched.

As a rule, however, the flock breaks up into pairs; and then a neat, well-made nest is built in the fork of a branch, lined with horsehair; or, oftener still, a Leñatero's nest is seized, the Bay-wings fighting with great spirit to get possession, and in it, or on it, their own nest is made. Like their relations, the Common Cow-bird, they seem strongly attracted by domed nests, and yet shrink from laying in the dark interior; as a rule when they have captured a Leñatero's nest they break a hole in the side and so admit the light and form an easy entrance. One summer a pair of Bay-wings attacked a Leñatero's nest on one of my trees; the fighting was kept up for three or four days, and then at the foot of the tree I found five young Leñateros, fully fledged, which had been pecked to death and thrown out of the nest.

The eggs of the Bay-wing are five in number, nearly round, and densely marked with dusky reddish brown.

Once I observed two young Bay-wings following a Yellow-breast (_Pseudoleistes virescens_) with their usual peculiar hunger-cry, and while I watched them they were fed several times by their foster-parents. Naturally I concluded that the Bay-winged Cow-bird is sometimes parasitical on other species, but I never saw anything afterwards to confirm me in that belief, and I believe now that I was mistaken, and that the young Bay-wings were not _real_ Bay-wings, but the young of _Molothrus rufoaxillaris_.

97. AGELÆUS THILIUS (Mol.).

(YELLOW-SHOULDERED MARSH-BIRD.)

+Agelæus thilius+, _Burm. La-Plata Reise_, ii. p. 492 (Mendoza, S. Juan, Catamarca); _Scl. et Salv. Nomencl._ p. 37; _Durnford, Ibis_, 1876, p. 159 (Buenos Ayres), 1877, p. 33 (Chupat), p. 174 (Buenos Ayres), et 1878, p. 394 (Chupat); _White, P. Z. S._ 1882, p. 602 (Buenos Ayres); _Döring, Exp. al Rio Negro, Zool._ p. 40 (Colorado); _Barrows, Bull. Nutt. Orn. Cl._ viii. p. 134 (Entrerios); _Scl. Cat. B._ xi. p. 343.

_Description._--Black; lesser upper and under wing-coverts yellow; bill and feet black: whole length 5·5 inches, wing 3·6, tail 2·7. _Female_: above pale brown striated with black; distinct superciliaries white; beneath paler, cineraceous white with black striations; smaller, and bill shorter.

_Hab._ S. Peru, Chili, Paraguay, and Argentina.

This bird is abundant everywhere on the pampas, and does not migrate, but inhabits marshy situations in summer, building its nest amongst the rushes, and in winter ranges over the country. The male is entirely of an intense black, except the shoulders, which are pure yellow; the female is dull grey with fuscous markings, and, as was long ago remarked by Azara, the grey-plumaged are very much more numerous than the black individuals. The young birds are like the females, and possibly do not acquire the full black plumage until the second year, which would account for the great number of grey birds.

These birds are extremely sociable, being seen in flocks all the year round, even during the breeding-season; in winter a great many males separate themselves from the females, and are found associating together in flocks of from thirty to forty individuals.

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.

Concerning the plumage of this species Mr. Barrows writes:--"Late in March, 1881, we found this species in large flocks on the Pigué, and it was a beautiful sight to see a hundred or more fluttering about among the snowy plumes of the pampas grass, and displaying their rich black and yellow dress. Unlike most other birds obtained at that time, their plumage seemed nearly as bright and fresh as in summer."

99. AGELÆUS RUFICAPILLUS, Vieill.

(RED-HEADED MARSH-BIRD.)

+Agelæus ruficapillus+, _Scl. Cat. B._ xi. p. 347. +Xanthosomus ruficapillus+, _Scl. et Salv. P. Z. S._ 1869, p. 159 (Buenos Ayres); _iid. Nomencl._ p. 37; _White, P. Z. S._ 1882, p. 602 (Salta, Catamarca). +Chrysomus frontalis+, _Burm. La-Plata Reise_, ii. p 492 (Paraná).

_Description._--Glossy blue-black; crown of head and middle of throat dark chestnut; bill and legs black: whole length 7·5 inches, wing 3·7, tail 2·9.

_Hab._ Argentina and Paraguay.

The sexes are alike in this species: the crown of the head is rufous, and with this exception the whole plumage a rich glossy blue-black. The beauty of the bird and its delicate, plaintive voice would no doubt make it a favourite with man if he saw more of it, only it lives and breeds in marshes, and does not come near his habitations. The Red-heads are gregarious and migratory. The flock can scarcely be said to break up in the breeding-season, as the birds all make their nests near together in the reeds. The nest is placed about one or two feet above the water, is about six inches in depth, and made of leaves and aquatic grasses woven together. The eggs are four, pointed, with a white or pale bluish ground, and spotted with black at the larger end.

The song of the Red-head is quite unique in character. It begins with a low, hollow-sounding note, then the voice changes to a clear, sorrowful tone, rising in a rapid succession of short notes, and falling again in longer ones.

After the breeding-season the birds fly about in flocks of two or three hundred individuals, and sing in concert on the trees.

Their chirp has a peculiar metallic sound, and can be imitated by tapping on the edge of a copper bell with the finger-nail.

100. LEISTES SUPERCILIARIS, Bp.

(RED-BREASTED MARSH-BIRD.)

+Leistes superciliaris+, _Hudson, P. Z. S._ 1870, p. 333 (Buenos Ayres); _Scl. et Salv. Nomencl._ p. 38; _Durnford, Ibis_, 1877, p. 175 (Buenos Ayres); _White, P. Z. S._ 1882, p. 602 (Salta); _Barrows, Bull. Nutt. Orn. Cl._ viii. p. 136 (Entrerios); _Scl. Cat. B._ xi. p. 349. +Trupialis guianensis+, _Burm. La-Plata Reise_, ii. p. 490 (Banda Oriental).

_Description._--Brownish black; superciliaries pale brown; bend of the wing and body beneath from the chin to the middle of the belly bright scarlet; bill and legs black; length 7·0 inches, wing 4·0, tail 2·5. _Female_ pale brown, above variegated with black, below stained with red on the breast; flanks and lower belly striated with black; tail cinereous brown, with black cross bars.

_Hab._ Argentina, Paraguay, and E. Brazil.

The most interesting point concerning this species is the very great difference in habits, as well as appearance, existing between the sexes. In form it resembles the Starling of Europe, but is a trifle smaller and has a shorter tail. The male is black, the upper parts faintly mottled with yellowish grey; there is a straw-coloured stripe over the eye; the throat and breast bright crimson. The female is a smaller bird, and in colour dull fulvous grey, mottled with fuscous; the red tint on the breast scarcely perceptible.

These birds are migratory, and appear everywhere in the eastern part of the Argentine country early in October, arriving singly, after which each male takes up a position in a field or open space abounding with coarse grass and herbage, where he spends most of the time perched on the summit of a tall stalk or weed, his glowing crimson bosom showing at a distance like some splendid flower above the herbage. At intervals of two or three minutes he soars vertically up to a height of twenty or twenty-five yards to utter his song, composed of a single long, powerful, and rather musical note, ending with an attempt at a flourish, during which the bird flutters and turns about in the air; then, as if discouraged at his failure, he drops down, emitting harsh guttural chirps, to resume his stand. Meanwhile, the female is invisible, keeping closely concealed under the long grass. But at length, attracted perhaps by the bright bosom and aerial music of the male, she occasionally exhibits herself for a few moments, starting up with a wild, zigzag flight, like a Snipe flushed from its marsh, and, darting this way and that, presently drops into the grass once more. The moment she appears above the grass the male gives chase, and they vanish from sight together. Thus, while in colour, habits, language, and even in its manner of soaring up like a rocket to let off its curious melody, the male is the most conspicuous of small birds, the female, acted on in an opposite direction by natural selection, has been, so to speak, effaced. While flying, they do not look like birds of the same species: the male moves with wings rapidly fluttered, like a Starling, but with a slower, more laborious flight, and without deviating; the female, in her eccentric movements in the air, reminds one of a large moth driven from its hiding-place, and flying about confused with the glare of noon.

The nest is made of dry grass on the ground, so cunningly concealed that it is most difficult to find. The eggs are four, white, spotted with reddish brown. When they have young, I have never been able to detect the female flying about in search of food.

All through the summer these birds are solitary, but when migrating in the autumn, though many are seen travelling singly, and appear very conspicuous as they fly laboriously in a straight line, at an altitude of about twenty yards from the surface, others are seen making their journey in small flocks or parties composed of six to a dozen individuals. These are the males. The females travel separately, in twos or threes or singly, flying nearer to the earth, with frequent pauses, when the wings cease beating, and intervals of gliding, also darting occasionally to one side, as if the bird had suddenly taken fright.

101. AMBLYRHAMPHUS HOLOSERICEUS (Scop.).

(SCARLET-HEADED MARSH-BIRD.)

+Amblyrhamphus holosericeus+, _Hudson, P. Z. S._ 1870, p. 114 (Buenos Ayres); _Scl. et Salv. Nomencl._ p. 37; _Durnford, Ibis_, 1877, p. 174 (Buenos Ayres); _Gibson, Ibis_, 1880, p. 18 (Buenos Ayres); _White, P. Z. S._ 1882, p. 602 (Buenos Ayres); _Barrows, Bull. Nutt. Orn. Cl._ viii. p. 135 (Entrerios); _Scl. Cat. B._ xi. p. 351. +Amblyrhamphus ruber+, _Burm. La-Plata Reise_, ii. p. 491 (Entrerios, Santa Fé, Paraná).

_Description._--Black; whole head and neck all round, and upper breast and thighs scarlet; bill and feet black: total length 9·5 inches, wing 4·5, tail 4·0. _Female_ similar. _Young_ uniform black.

_Hab._ Paraguay, Uruguay, and Argentina.

Azara named this species _Tordo negro cabeza roxa_; it is also called _Boyero_ (ox-herd) by country people, from its note resembling the long whistle of a drover; and sometimes _Chisel-bill_, from the peculiar conformation of the beak, which is long, straight, and has a broad fine point like a chisel. In both sexes the plumage of the head and neck is scarlet, of an exceedingly brilliant tint, all other parts intense black. These birds are lively, active, and sociable, going in flocks of from half-a-dozen to thirty individuals; they remain all the year, and inhabit the marshes, from which they seldom wander very far, but seek their insect food in the soft decaying rushes. They are common on the swampy shores of the Plata, and when seen at a distance, perched in their usual manner on the summits of the tall rushes, their flame-coloured heads shine with a strange glory above the sere sombre vegetation of the marshes. The long whistling note above mentioned is their only song, but it varies considerably, and often sounds as mellow and sweet as the whistle of the European Blackbird.

The nest is an ingenious structure of dry grasses, fastened to the upright stems of an aquatic plant, three or four feet above the water. The eggs are four, in size and form like those of the English Song-Thrush, spotted somewhat sparsely with black on a light blue ground.

The young birds are entirely black at first, and afterwards assume on the head and neck a pale terra-cotta red, which gradually deepens to vivid scarlet.

102. PSEUDOLEISTES VIRESCENS (Vieill.).

(YELLOW-BREASTED MARSH-BIRD.)

+Pseudoleistes virescens+, _Hudson, P. Z. S._ 1870, p. 549, et 1874, p. 156 (Buenos Ayres); _Scl. et Salv. Nomencl._ p. 37; _Durnford, Ibis_, 1877, p. 175, et 1878, p. 59 (Buenos Ayres); _Gibson, Ibis_, 1880, p. 31 (Buenos Ayres); _White, P. Z. S._ 1882, p. 602 (Buenos Ayres); _Barrows, Bull. Nutt. Orn. Cl._ viii. p. 135 (Entrerios); _Scl. Cat. B._ xi. p. 352. +Leistes anticus+, _Burm. La-Plata Reise_, ii. p. 491 (Paraná).

_Description._--Above and below dark olive-brown; lesser upper wing-coverts, under wing-coverts, and middle of the abdomen yellow; bill black; feet dark brown: total length 9·5 inches, wing 4·6, tail 3·8. _Female_ similar.

_Hab._ S. Brazil, Paraguay, Uruguay, and Argentina.