Naturalists are much divided in their opinion concerning the periodical appearance and disappearance of swallows.—Some assert, that they remove from climate to climate, at those particular seasons when winged insects, their natural food, fail in one country and are plentiful in another, where they likewise find a temperature of air better suited to their constitution. In support of this opinion, we have the testimony of Sir Charles Wager, and of Mr. Adamson, who, in the account of his voyage, informs us, that, about fifty leagues from the coast of Senegal, four swallows settled upon the ship, on the 6th day of October; that these birds were taken; and that he knew them to be the true swallow of Europe, which he conjectures were then returning to the coast of Africa.
But Mr. Daines Barrington, in a curious essay on this subject, has adduced many arguments and facts, to prove that no birds, however strong and swift in their flight, can possibly fly over such large tracts of ocean as has been commonly supposed. He is of opinion, therefore, that the swallows mentioned by Mr. Adamson, instead of being on their passage from Europe, were only fluttering from the Cape de Verde islands to the continent of Africa; a much nearer flight, but to which they seemed to be unequal, as they were obliged, from fatigue, to alight upon the ship, and fall into the hands of the sailors. And Mr. Kalm, another advocate for the torpidity of swallows during the winter, having remarked, however, that he himself had met with them nine hundred and twenty miles from any land; Mr. Barrington endeavours to explain these, and similar facts, by supposing that birds discovered in such situations, instead of attempting to cross large branches of the ocean, have been forcibly driven from some coast by storms, and that they would naturally perch upon the first vessel they could see.
In a word, Mr. Barrington is further of opinion, with some other naturalists, that the swallows do not leave this island at the end of autumn, but that they lie in a torpid state, till the beginning of summer, in the banks of rivers, in the hollows of decayed trees, the recesses of old buildings, the holes of sand-banks, and in similar situations. Among other facts, Mr. Barrington communicated one to Mr. Pennant, that “numbers of swallows have been found in old dry walls, and in sand-hills, near the seat of the late Lord Belhaven, in East Lothian; not once only, but from year to year; and that, when they were exposed to the warmth of a fire, they revived.”
These, and other facts of the same kind, are allowed to be incontrovertible; and Mr. Pennant, in particular, infers from them, that “we must divide our belief relative to these two so different opinions, and conclude, that one part of the swallow tribe migrate, and that others have their winter quarters near home.”
But there are still more wonderful facts related. Mr. Kalm remarks, that “swallows appear in the Jerseys about the beginning of April; that, on their first arrival, they are wet, because they have just emerged from the sea or lakes, at the bottom of which they had remained, in a torpid state, during the whole winter.” Other naturalists have asserted, that swallows pass the winter immersed under the ice, at the bottom of lakes, or beneath the waters of the sea. Olaus Magnus, archbishop of Upsal, seems to have been the first who adopted this opinion. He informs us, that “swallows are found in great clusters at the bottoms of the northern lakes, with mouth to mouth, wing to wing, foot to foot, and that in autumn they creep down the reeds to their subaqueous retreats.” In other instances, Mr. Pennant remarks, the good archbishop did not want credulity. But the submersion of the swallows under water does not rest upon his testimony alone. Klein asserts the same; and gives the following account of the manner of their retiring, which he had from some countrymen:
“They asserted, that the swallows sometimes assembled in numbers on a reed, till it broke, and sunk them to the bottom; that their immersion was preceded by a kind of dirge, which lasted more than a quarter of an hour; that others united, laid hold of a straw with their bills, and plunged down in society; that others, by clinging together with their feet, formed a large mass, and in this manner committed themselves to the deep.” Bishop Pontoppidan asserts, that clusters of swallows, in their torpid winter state, have sometimes been found by fishermen, among reeds and bushes in lakes; and he charges Mr. Edwards with having, in his Natural History of Birds, groundlessly contradicted this incontestable truth. And Mr. Heerkens, a celebrated Dutch naturalist, in a poem on the birds of Friesland, speaks in positive terms of the torpid state, and submersion, of the swallows:
“Ere winter his somnif’rous power exerts,
Six dreary months the swallow-tribes are seen
In various haunts conceal’d; in rocks, and caves,
And structures rude, by cold benumb’d, asleep;
Bill within bill inserted, clust’ring thick:
Or solitary some, of mate bereft.
But, wonderful to tell! some lie immers’d,
Inanimate, beneath the frigid waves,
As if a species of the finny kinds.”
Mr. Heerkens, after reciting many instances, and producing in his notes many authorities, of swallows having been found in a torpid state, proceeds, in his poem, to describe, very minutely, their ascent out of the water. The drowsy birds appear on the shore, as if unconscious still of life. Some inhale the soft breeze, like one of the finny tribe exiled from its stream. Some begin to adjust their dishevelled wings.—Others, almost revived, essay, with busy bill, to assist their aged companions. All, at length, restored to the unrestrained use of their wings, range, in numerous flights, the aërial way.
Two reasons have, been adduced to prove this supposed submersion of swallows impossible. “In the first place, (says Mr. Smellie,) no land animal can exist so long without some degree of respiration. The otter, the seal, and water fowls of all kinds, when confined under the ice, or entangled in nets, soon perish; yet it is well known, that animals of this kind can remain much longer under water than those who are destitute of that peculiar structure of the heart, which is necessary for any considerable residence beneath that penetrating element.”
Mr. John Hunter, in a letter to Mr. Pennant, informs us, “that he had dissected many swallows, but found nothing in them different from other birds, as to the organs of respiration; that all those animals which he had dissected, of the class that sleep during the winter, such as lizards, frogs, &c. had a very different conformation as to those organs; that all those animals, he believes, do breathe in their torpid state, and, as far as his experience reaches, he knows they do; and that, therefore, he esteems it a very wild opinion, that terrestrial animals can remain any long time under water without drowning.” Another argument against their submersion arises from the specific gravity of the animals themselves. Of all birds, the swallow tribes are perhaps the lightest. Their plumage, and the comparative smallness of their weight, indicates that Nature destined them to be almost perpetually on the wing, in quest of food. From this specific lightness, the submersion of swallows, and their continuing for months underwater, amount to a physical impossibility. Even water fowls, when they wish to dive, are obliged to rise and plunge with considerable exertion, in order to overcome the resistance of the water. Klein’s idea of swallows employing reeds and straws as means of submersion, is rather ludicrous; for these light substances, instead of being proper instruments for assisting them to reach the bottom, would infallibly contribute to support them on the surface, and prevent the very object of their intention. Besides, admitting the possibility of their reaching the bottom of lakes and seas, and supposing they could exist for several months without respiration, what would be the consequence? The whole would soon be devoured by otters, seals, and fishes, of various kinds. Nature is always anxious for the preservation of its species. But if the swallow tribes were destined to remain torpid during the winter months, at the bottom of lakes and seas, she would act in opposition to her own intentions; for, in a season or two, the whole genus would be annihilated.