Popular Science Monthly/Volume 7/July 1875/The Biography of a Bird
THE bird which is the subject of this sketch is familiar to all who walk in green pastures and beside still waters; for in such haunts do the Bank-Swallows congregate in merry companies, making up for their want of companionship with man, which is so characteristic of the other hirundines, by a large sociability among themselves. Conservator of ancient ways, it is almost the only swallow which has not attached itself to humanity as soon as it had opportunity, and changed from a savage to a civilized bird. Perhaps it, too, has tried it, long ago, and voluntarily returned to the fields; for our bank-swallow is a cosmopolite, and has watched the rise and fall of all the dynasties and nationalities that have grouped the centuries into eras, from Nineveh to San Francisco. It is at present an inhabitant of all Europe and eastward to China; of a large part of Africa, especially in winter; and throughout North America, the West Indies, Central America, and the northern Andean countries. On both continents its wanderings extend to the extreme north, where, in Alaska, it is one of the commonest summer visitors. So this modest little bird, smallest of his kind, is entitled to our respect as a traveler at least; and, to compare the habits and appearance of the representatives in different portions of the globe of so widely distributed a species, becomes a most interesting study.
Cotyle riparia, the bank-swallow, sand-martin, sand-swallow, river-swallow, l'hirondelle de rivage, or back-svala, is generally diffused over the Northern Hemisphere though very unequally, avoiding those spots unfavorable to them. In this distribution they seem to have been somewhat influenced by man, though owing him no other favors than the incidental help of railroad-cuttings and sand-pits which have increased the sites suitable for their nests and enabled them to spread inland.
It is one of the earliest birds to arrive in the spring, appearing in Old England during the last week in March, and in New England early in May, many passing on to the shores of the Arctic Ocean, where Richardson, at the mouth of the Mackenzie, and Dall, on the Yukon, found them breeding in immense numbers. In these high latitudes its summer is necessarily a brief one, and September finds them back again picking up their congeners for company on the southward journey.
Where these and other swallows spend the winter was a hotly debated question among ornithologists at the beginning of the present century; some affirming that they migrated with the sun, while others, believing it impossible that such small and delicate birds could endure the great fatigue and temperatures incident to such a migration, held that they regularly hibernated, during the cold weather, sinking into the mud at the bottom of ponds, like frogs, or curling up in deep, warm crannies, like bats, and remaining torpid until revived by the warmth of spring. Of this latter opinion was White, of Selborne, who alludes to it again and again, and Sir Thomas Forster wrote a "Monograph of British Swallows," apparently with no other object than to present the arguments for and against the theory of their annual submersion and torpidity. One of the difficulties which the submersionists put in the way of the migrationists was the frequent accidental and isolated appearance of the swallow before its usual time—a fact which has occasioned a proverb in almost every language. The French have, "Une hirondelle ne fait pas le printemps;" the Germans, "Eine Schwalbe macht kleinen Frühling;" the Dutch, "Een zwaluw maak geen zomer;" the Italians, "Una rodine non fa primavera;" the Swedes, "En svala gov ingen sommar;" which all mean. One swallow doth not make a summer. The story is well known of a thin brass plate having been fixed on a swallow with this inscription: "Prithee, swallow, whither goest thou in winter?" The bird returned next spring with the answer subjoined: "To Anthony, of Athens. Why dost thou inquire?"
Out of this controversy, evidence of their sudden autumnal adjournment to Africa accumulated in England. Wilson, in this country, showed that their advance could be traced in the spring from New Orleans to Lake Superior and back again, and their regular migration soon came to be acknowledged. Then attention was turned to the season, manner and limits of their migrations, and it was found that, taking advantage of favorable winds, immense flocks of swallows—and many other birds of passage as well—flying very high, passed each fall from the coast of England to the coast of Africa, and from Continental Europe across the Mediterranean direct, whence they spread southward almost to the Cape of Good Hope. No sooner had the spring fairly opened than they were suddenly back again, very much exhausted at first with their long-sustained effort, but speedily recuperated and "diligent in business." Our own migrants, as I have mentioned, winter in Central America and the West Indies, or still farther south.
Their flight is rapid, but unsteady, "with odd jerks and vacillations not unlike the motions of a butterfly," as White describes it; and continues: "Doubtless the flight of all hirundines is influenced by and adapted to the peculiar sort of insects which furnish their food. Hence it would be worth inquiry to examine what particular genus of insects affords the principal food of each respective species of swallow." They are constantly on the wing, skimming low over land and loch, pausing not even to drink or bathe, but simply dropping into some limpid lake as they sweep by to sip a taste of water, or cleanse their dirty coats. It seems strange, then, that birds who sustain the unremitting exertion of a flight scarcely less than 100 miles an hour in speed, during the whole of a long summer's day, should not be thought capable of the transition from England to Africa. However, at that time it was not well understood what long-continued flight small birds actually do make, as, for instance, from our coast to the Bahamas, or even across to Ireland, or from Egypt to Heligoland, 1,200 miles, which is passed over at a single flight by a certain tiny warbler, in every migration.
The bank-swallow is not a musical bird—a faint, squeaking chirrup being all its voice can accomplish. Nor is it a handsome bird, simply sooty-brown above, white beneath, with a brown breast. To its grace of motion, and charming home-life, we attribute that in it which attracts us so much.
Although probably the least numerous of all the swallows, they do not seem so, because of the great companies which are to be seen together wherever they are to be found at all; and because, leading a more sequestered life, they are not usually brought into direct comparison with house-martins and chimney-swifts. Eminently social in their habits, they congregate not only at the time of migration (then, indeed, least of all), and in the construction of their homes, but sometimes alight in great flocks on the reeds by the river-side and on the beach, where Sir William Jardine saw them "partly resting and washing, and partly feeding on a small fly, which was very abundant." Yet you will occasionally notice stray individuals associating with other swallows.
The secret of the local distribution of the bank-swallows lies in the presence or absence of vertical exposures of soil suitable for them to penetrate for the burrows, at the inner end of which the nest is placed. Firm sand, with no admixture of pebbles, is preferred, and in such an exposure, be it sea-shore, river-bank, sand-pit, or railway-cutting, the face will be fairly honey-combed with burrows, so that we can readily believe that Mr. Dall counted over 700 holes in one bluff in Alaska. These are usually very close together, and the wonder is how the birds can distinguish their own doors. If mistakes do occur, I imagine they are very polite about it, for I know of no more peaceable bird than they. The mode in which this perforation, requiring an amount of labor rare among birds, is performed, is well described by Mr. Rennie, in his "Architecture of Birds:"
Sometimes the nest is carried to a far greater depth than two or three feet, as in a case observed by Mr. Fowler, in Beverly, Massachusetts, where, in order to get free of a stony soil where pebbles might be dislodged and crush the eggs, the tunnel was carried in nine feet, while neighboring birds in better soil only went a third as far. In one place the burrows will be close to the top of the bluff, in another near the bottom, according as fancy dictates, or the birds have reason to fear this or that enemy. English writers agree that occasionally their bank-swallows do not dig holes, but lay in the crannies of old walls, and in hollows of trees. This is never done, that I am aware of, in the United States; but in California a closely allied species, the rough-winged swallow, "sometimes resorts to natural clefts in the banks or adobe buildings, and occasionally to knot-holes." On the great Plains, however, our Cotyle burrows in the slight embankments thrown up for a railway-bed, in lieu of a better place,
"How long does it take the bird to dig his cavern under ordinary circumstances?" is a question which it would seem hard to answer, considering the cryptic character of his work. Mr. W. H. Dall says four days suffice to excavate the nest. Mr. Morris, a close observer of British birds, says, per contra, that a fortnight is required, and that the bird removes twenty ounces of sand a day. Male and female alternate in the labor of digging, and in the duties of incubation.
When the female is sitting, you may thrust your arm in and grasp her, and, notwithstanding the noise and violence attending the enlargement of the aperture of her nest-hole, she will sit resolutely on, and allow herself to be taken in the hand with scarcely a struggle or sign of resistance—even of life, sometimes. The young are fed with the large insects which the parents catch, particularly those sub-aquatic . sorts which hover near the surface of still water; and White mentions instances where young swallows were fed with dragon-flies nearly as long as themselves. The young do not leave the nest until they are about ready to take full care of themselves. Finally, they are pushed off by the parents to make way for the second brood, and, inexperienced in the use of their wings, many fall a prey to crows and small hawks that lie in wait ready to pounce upon the first poor little fellow that launches upon the untried air. Those that manage to run the gantlet of the hawks, collect in small companies by themselves and have a good time hunting by day, and roosting at night among the river-reeds, until the autumn migration. "At this time Salerne observes," says Latham, "that the young are very fat, and in flavor scarcely inferior to the ortolan." Sometimes the parents forsake their progeny in the nest, and seem generally to care less for them than is usual among swallows.
But not the young alone are exposed to enemies. It would seem as though the situation of the nest precluded invasion, yet if they are near the haunts of the house-sparrow they are sure to be dispossessed of their homes by that buccaneer. Snakes, too, can sometimes reach their holes; weasels, like that one Mr. Hewitson tells us of, are often sharp enough to make their entrée from above: school-boys regard the pink-white eggs a fine prize; and, last and worst of all, the bank-swallows are many times utterly worried out of their galleries by fleas and young horse-flies, which swarm and increase in their nests until the bird finds endurance no longer a virtue, and digs a new latebra.