When shooting birds to preserve I used to keep an anxious eye on the movements of the Chimangos flying about, for I have had some fine specimens carried off or mutilated by these omnipresent robbers. One winter day I came across a fine Myiotheretes rufiventris, a pretty and graceful Tyrant-bird, rather larger than the Common Thrush, with a chocolate and silver-grey plumage. It was rare in that place, and, anxious to secure it, I fired a very long shot, for it was extremely shy. It rose up high in the air and flew off apparently unconcerned. What, then, was my surprise to see a Chimango start off in pursuit of it! Springing on to my horse, I followed, and before going half a mile noticed the Tyrant-bird beginning to show signs of distress. After avoiding several blows aimed by the Chimango, it flew down and plunged into a cardoon bush. There I captured it, and when skinning it to preserve found that one small shot had lodged in the fleshy portion of the breast. It was a very slight wound, yet the Chimango with its trained sight had noticed something wrong with the bird from the moment it flew off, apparently in its usual free buoyant manner.
On another occasion I was defrauded of a more valuable specimen than the Tyrant-bird. It was on the east coast of Patagonia, when one morning, while seated on an elevation, watching the waves dashing themselves on the shore, I perceived a shining white object tossing about at some distance from land. Successive waves brought it nearer, till at last it was caught up and flung far out on to the shingle, fifty yards from where I sat; and instantly, before the cloud of spray had vanished, a Chimango dashed down upon it. I jumped up and ran down as fast as I could, and found my white object to be a Penguin, apparently just killed by some accident out at sea, and in splendid plumage; but, alas! in that moment the vile Chimango had stripped off and devoured the skin from its head, so that as a specimen it was hopelessly ruined.
As a rule, strong healthy birds despise the Chimango; they feed in his company; his sudden appearance causes no alarm, and they do not take the trouble to persecute him; but when they have eggs or young he is not to be trusted. He is not easily turned from a nest he has once discovered. I have seen him carry off a young Tyrant-bird (Milvulus tyrannus), in the face of such an attack from the parent birds that one would have imagined not even an Eagle could have weathered such a tempest. Curiously enough, like one of the boldest of our small Hawks (Tinnunculus cinnamominus), they sometimes attack birds so much too strong and big for them that they must know the assault will produce more annoyance than harm. I was once watching a flock of Coots feeding on a grassy bank, when a passing Chimango paused in its flight, and, after hovering over them a few moments, dashed down upon them with such impetuosity that several birds were thrown to the ground by the quick successive blows of its wings. There they lay on their backs, kicking, apparently too much terrified to get up, while the Chimango deliberately eyed them for some moments, then quietly flew away, leaving them to dash into the water and cool their fright. Attacks like these are possibly made in a sportive spirit, for the Milvago is a playful bird, and, as with many other species, bird and mammal, its play always takes the form of attack.
Its inefficient weapons compel it to be more timid than the Hawk, but there are many exceptions, and in every locality individual birds are found distinguished by their temerity. Almost any shepherd can say that his flock is subject to the persecutions of at least one pair of lamb-killing birds of this species. They prowl about the flock, and watch till a small lamb is found sleeping at some distance from its dam, rush upon it, and, clinging to its head, eat away its nose and tongue. The shepherd is then obliged to kill the lamb; but I have seen many lambs that have been permitted to survive the mutilation, and which have grown to strong, healthy sheep, though with greatly disfigured faces. One more instance I will give of the boldness of a bird of which Azara, greatly mistaken, says that it might possibly have courage enough to attack a mouse, though he doubts it. Close to my house, when I was a boy, a pair of these birds had their nest near a narrow path leading through a thicket of giant thistles, and every time I traversed this path the male bird, which, contrary to the rule with birds of prey, is larger and bolder than the female, would rise high above me, then dashing down, strike my horse a violent blow on the forehead with its wings. This action it would repeat till I was out of the path. I thought it very strange the bird never struck my head; but I presently discovered that it had an excellent reason for what it did. The gauchos ride by preference on horses never properly tamed, and one neighbour informed me that he was obliged every day to make a circuit of half a mile round the thistles, as the horses he rode became quite unmanageable in the path, they had been so terrified with the attacks of this Chimango.
Where the intelligence of the bird appears to be really at fault is in its habit of attacking a sore-backed horse, tempted thereto by the sight of a raw spot, and apparently not understanding that the flesh it wishes to devour is an inseparable part of the whole animal. Darwin has noticed this curious blunder of the bird; and I have often seen a chafed saddle-horse wildly scouring the plain closely pursued by a hungry Chimango determined to dine on a portion of him.
In the hot season, when marshes and lagoons are drying up, the Chimango is seen associating with Ibises and other waders, standing knee-deep in the water and watching for tadpoles, frogs, and other aquatic prey. He also wades after a very different kind of food. At the bottom of pools, collected on clayey soil after a summer shower, an edible fungus grows of a dull greenish colour and resembling gelatine. He has found out that this fungus is good for food, though I never saw any other creature eating it. In cultivated districts he follows the plough in company with the black-headed gulls, Molothri, Guira cuckoos, and tyrant-birds, and clumsily gleans amongst the fresh-turned mould for worms and larvæ. He also attends the pigs when they are rooting on the plain to share any succulent treasure-trove turned up by their snouts; for he is not a bird that allows dignity to stand between him and his dinner. In the autumn, on damp, sultry days, the red ants, that make small conical mounds on the pampas, are everywhere seen swarming. Rising high in the air they form a little cloud or column, and hang suspended for hours over the same spot. On such days the Milvagos fare sumptuously on little insects, and under each cloud of winged ants several of them are to be seen in company with a few Flycatchers, or other diminutive species, briskly running about to pick up the falling manna, their enjoyment undisturbed by any sense of incongruity.
Before everything, however, the Chimango is a vulture, and is to be found at every solitary rancho sharing with dogs and poultry the offal and waste meat thrown out on the dust-heap; or, after the flock has gone to pasture, tearing at the eyes and tongue of a dead lamb in the sheepfold. When the hide has been stripped from a dead horse or cow on the plains, the Chimango is always first on the scene. While feeding on a carcass it incessantly utters a soliloquy of the most lamentable notes, as if protesting against the hard necessity of having to put up with such carrion fare—long, querulous cries, resembling the piteous whines of a shivering puppy chained up in a bleak backyard and all its wants neglected, but infinitely more doleful in character. The gauchos have a saying comparing a man who grumbles at good fortune to the Chimango crying on a carcass; an extremely expressive saying to those who have listened to the distressful wailings of the bird over its meat. In winter a carcass attracts a great concourse of the Black-backed Gulls; for with the cold weather these vultures of the sea abandon their breeding-places on the Atlantic shores to wander in search of food over the vast inland pampas. The dead beast is quickly surrounded by a host of them, and the poor Chimango crowded out. One at least, however, is usually to be seen perched on the carcass tearing at the flesh, and at intervals with outstretched neck and ruffled up plumage uttering a succession of its strange wailing cries, reminding one of a public orator mounted on a rostrum and addressing harrowing appeals to a crowd of attentive listeners. When the carcass has been finally abandoned by foxes, armadillos, gulls, and caracaras, the Chimango still clings sorrowfully to it, eking out a miserable existence by tearing at a fringe of gristle and whetting his hungry beak on the bones.
Though an inordinate lover of carrion, a wise instinct has taught it that this aliment is unsuited to the tender stomachs of its fledglings; these it feeds almost exclusively on the young of small birds. In November the Chimangos are seen incessantly beating over the cardoon bushes, after the manner of Hen-harriers; for at this season in the cardoons breeds the Synallaxis hudsoni. This bird, sometimes called Téru-réru del campo by the natives, is excessively shy and mouse-like in its habits, seldom showing itself, and by means of strong legs and a long, slender, wedge-like body is able too glide swiftly as a snake through and under the grass. In summer one hears its long melancholy trilling call-note from a cardoon bush, but if approached it drops to the ground and vanishes. Under the densest part of the cardoon bush it scoops out a little circular hollow in the soil, and constructs over it a dome of woven grass and thorns, leaving only a very small aperture: it lines the floor with dry horse-dung, and lays five buff-coloured eggs. So admirably is the nest concealed that I have searched every day for it through a whole breeding-season without being rewarded with a single find. Yet they are easily found by the Chimango. In the course of a single day I have examined five or six broods of young Chimangos, and by pressing a finger in their distended crops, made them disgorge their food, and found in every instance that they had been fed on nothing but the young of the Téru-réru. I was simply amazed at this wholesale destruction of the young of a species so secret in its nesting-habits; for no eye, even of a Hawk, can pierce through the leafage of a cardoon bush, ending near the surface in an accumulated mass of the dead and decaying portions of the plant. The explanation of the Chimango’s success is to be found in the loquacious habit of the fledglings it preys on, a habit common in the young of Dendrocolaptine species. The intervals between the visits of the parent birds with food they spend in conversing together in their high-pitched tones. If a person approaches the solid fabric of the Ovenbird (Furnarius rufus), when there are young in it, he will hear shrill laughter-like notes and little choruses, like those uttered by the old birds, only feebler; but in the case of that species no harm can result from the loquacity of the young, since the castle they inhabit is impregnable. Hovering over the cardoons, the Chimango listens for the stridulous laughter of the fledglings, and when he hears it the thorny covering is quickly pierced and the dome broken into.
Facts like this bring before us with startling vividness the struggle for existence, showing what great issues in the life of a species may depend on matters so trivial, seemingly, that to the uninformed mind they appear like the merest dust in the balance, which is not regarded. And how tremendous and pitiless is that searching law of the survival of the fittest in its operations when we see a species like this Synallaxis, in the fashioning and perfecting of which nature seems to have exhausted all her art, so exquisitely is it adapted in its structure, coloration, and habits to the one great object of concealment, yet apparently doomed to destruction through this one petty oversight—the irrepressible garrulity of the fledglings in their nest! It is, however, no oversight at all; since the law of natural selection is not prophetic in its action, and only preserves such variations as are beneficial in existing circumstances, without anticipating changes in the conditions. The settlement of the country has, no doubt, caused a great increase of Chimangos, and in some indirect way probably has served to quicken their intelligence; thus a change in the conditions which have moulded this Synallaxis brings a danger to it from an unexpected quarter. The situation of the nest exposes it, one would imagine, to attacks from snakes and small mammals, from bird-killing spiders, beetles, and crickets, yet these subtle ground foes have missed it, while the baby-laughter of the little ones in their cradle has called down an unlooked-for destroyer from above. It might be answered that this must be a very numerous species, otherwise the Chimango could not have acquired the habit of finding the nests; that when they become rarer the pursuit will be given over, after which the balance will readjust itself. But in numbers there is safety, especially for a feeble hunted species, unable from its peculiar structure to vary its manner of life. To such, the remark made by Darwin, that “rarity is the precursor to extinction,” applies with peculiar force.