Since in both sexes these feathers have the same form, it is clear that both can produce the same humming noise; but as the feathers of the hen are generally less than those of the cock-bird, the noise made by them is not so deep as in the other case.
Besides the significance which these tail-feathers have as a kind of musical instrument, their form may give a weighty character in the determination of a species standing very near one another, which have been looked upon as varieties.
This interesting discovery was first announced by M. Meves in an account of the birds observed by himself during a visit to the Island of Gottland, in the summer of the year 1856, which narrative was published at Stockholm in the following winter. In the succeeding summer, M. Meves showed his experiments to Mr. Wolley, whose services to Ornithology we have already noticed. The mysterious noise of the wilderness was reproduced in a little room in the middle of Stockholm: first, the deep bleat, now shown to proceed from the male Snipe, and then the fainter bleat of the female, both most strikingly true to nature, neither producible with any other feathers than the outer ones of the tail.
Mr. Wolley inquired of Mr. Meves how, issuing forth from the town on a summer ramble, he came to discover what had puzzled the wits and strained the eyes of so many observers. He freely explained how, in a number of "Naumannia," an accidental misprint of the word representing tail-feathers instead of wing-feathers,—a mistake which another author ridiculed—first led him to think on the subject. He subsequently examined in the Museum at Stockholm the tail-feathers of various species of Snipe, remarked their structure, and reasoned upon it. Then he blew upon them, and fixed them on levers that he might wave them with greater force through the air; and at the same time he made more careful observation than he had hitherto done in the living birds. In short, in him the obscure hint was thrown upon fruitful ground, whilst in a hundred other minds it had failed to come to light.
Dr. Walsh saw at Constantinople a Woodpecker, about the size of a Thrush, which was very active in devouring flies, and tapped woodwork with his bill with a noise as loud as that of a hammer, to disturb the insects concealed therein, so as to seize upon them when they appeared.
Among remarkable bird services should not be forgotten those of the Trochilos to the Crocodile. "When the Crocodile," says Herodotus, "feeds in the Nile, the inside of his mouth is always covered with bdella (a term which the translators have rendered by that of leech). All birds, except one, fly from the Crocodile; but this one bird, the Trochilos, on the contrary, flies towards him with the greatest eagerness, and renders him a very great service; for every time that the Crocodile comes to the land to sleep, and when he lies stretched out with his jaws open, the Trochilos enters and establishes himself in his mouth, and frees him from the bdella which he finds there. The Crocodile is grateful, and never does any harm to the little bird who performs for him this office."
This passage was long looked upon as a pleasant story, and nothing more; until M. Geoffroy St. Hilaire, during his long residence in Egypt, ascertained the story of Herodotus to be correct in substance, but inexact in details. It is perfectly true that a little bird does exist, which flies incessantly from place to place, searching everywhere, even in the Crocodile's mouth, for the insects which form the principal part of its nourishment. This bird is seen everywhere on the banks of the Nile, and M. Geoffroy has proved it to be of a species already described by Hasselquist, and very like the small winged Plover. If the Trochilos be in reality the little Plover, the bdella cannot be leeches, (which do not exist in the running waters of the Nile) but the small insects known as gnats in Europe. Myriads of these insects dance upon the Nile: they attack the Crocodile upon the inner surface of his palate, and sting the orifice of the glands, which are numerous in the Crocodile's mouth. Then the little Plover, who follows him everywhere, delivers him from these troublesome enemies; and that without any danger to himself, for the Crocodile is always careful, when he is going to shut his mouth, to make some motion which warns the little bird to fly away. At St. Domingo there is a Crocodile which very nearly resembles that of Egypt. This Crocodile is attacked by gnats, from which he would have no means of delivering himself (his tongue, like that of the Crocodile, being fixed) if a bird of a particular species did not give him the same assistance that the Crocodile of the Nile receives from the little Plover. These facts explain the passage in Herodotus, and demonstrate that the animal, there called bdella, is not a leech, but a flying insect similar to our gnat.
Exemplifications of instinct, intelligence, and reason in Birds are by no means rare, but this distinction must be made: instinctive actions are dependent on the nerves, intelligence on the brain; but that which constitutes peculiar qualities of the mind in man has no material organ. The Rev. Mr. Statham has referred to the theory of the facial angle as indicative of the amount of sagacity observable in the animal race, but has expressed his opinion that the theory is utterly at fault in the case of Birds; many of these having a very acute facial angle being considerably more intelligent than others having scarcely any facial angle at all. Size also seems to present another anomaly between the two races of Beasts and Birds; for while the Elephant and the Horse are among the most distinguished of quadrupeds for sagacity and instinct, the larger Birds seem scarcely comparable to the smaller ones in the possession of these attributes. The writer instances this by comparing the Ostrich and the Goose with the Wren, the Robin, the Canary, the Pigeon, and the Crow; and amusingly alludes to the holding of parliaments or convocations of birds of the last species, while the Ostrich is characterised in Scripture as the type of folly.
The author then refers to the poisoning of two young Blackbirds by the parent birds, when they found that they could neither liberate them nor permanently share their captivity. The two fledglings had been taken from a Blackbirds' nest in Surrey-square, and had been placed in a room looking over a garden, in a wicker cage. For some time the old birds attended to their wants, visited them regularly, and fed them with appropriate food; but, at last, getting wearied of the task, or despairing of effecting their liberation, they appear to have poisoned them. They were both found suddenly dead one morning, shortly after having been seen in good health; and on opening their bodies a small leaf, supposed to be that of Solanum Nigrum, was found in the stomach of each. The old birds immediately deserted the spot, as though aware of the nefarious deed befitting their name.
As an exemplification of instinct Dr. Horner states that Rooks built on the Infirmary trees at Hull, but never over the street. One year, however, a young couple ventured to build here: for eight mornings in succession the old Rooks proceeded to destroy the nest, when at last the young ones chose a more fitting place.