SWIFTS are extraordinary birds; there are no others like unto them; they are the most mysterious of the many mysterious products of natural selection; their athletic feats transcend the descriptive powers of the English language. What adjective is there of suitable application to a bird that speeds through the air without an appreciable effort at the rate of a hundred miles an hour, that traverses a thousand miles every day of its existence ?
These wonderful birds are everywhere common, yet much of their life history requires elucidation.
Probably not one man in fifty is able to distinguish between a swallow and a swift. Some think that "swift" and "swallow" are synonymous terms, while others believe that a swift is a kind of black swallow. As a matter of fact, the swift differs more widely from the swallow than the crow does from the canary. There is, it is true, a very strong professional likeness between the swift and the swallow, but this likeness is purely superficial; it is merely the resemblance engendered by similar modes of obtaining a livelihood. Both swallows and swifts feed exclusively on minute insects which they catch upon the wing, hence both have a large gape, light, slender bodies, and long, powerful wings. But speedy though it be, the swallow is not in the same class with the swift as a flyer. When both birds are in the hand nothing is easier than to tell a swift from a swallow or a martin. The latter have the ordinary passerine foot, which consists of three forwardly directed toes and a backwardly directed one. This foot enables a bird to perch, so that one frequently sees swallows seated on telegraph wires. But one never sees a swift on a perch, because all its four toes point forward. It cannot even walk. It spends its life in the air. It eats and drinks on the wing, it does everything, except sleeping and incubating, in the air.
But it is not often that one has a swallow or swift in the hand; it is difficult to get near enough to them to put salt on the tail, so that it is necessary to have some means of distinguishing them when sailing through the air. There is a very marked difference in the manner in which these birds use their wings. This is inimitably described by Mr. E. H. Aitken: "As a swallow darts along, its wings almost close against its sides at every stroke, and it looks like a pair of scissors opening and shutting. Now a swift never closes its wings in this way. It whips the air rapidly with the points of them, but they are always extended and evenly curved from tip to tip like a bow, the slim body of the bird being the arrow." As a swift speeds through the air it looks something like an anchor, with a short shaft and enormous flukes. If this be borne in mind, it is scarcely possible to mistake a swift for a swallow. Swifts are abundant in Calcutta, but one is not likely to come across a swallow there except when the moon happens to be blue.
The two swifts commonly seen in Calcutta are the Indian swift (Cypselus affinis) and the palm swift (C. batassiensis).
The latter need not detain us long. It is a small and weak edition of the former. It builds a cup-shaped nest on the under side of the great fan-like leaves of the toddy palm.
The Indian swift is, in size and appearance, much like the swift which visits England every summer, except for the fact that it has a white patch on the lower part of the back. The chin is white, but all the rest of the plumage, with the exception of the above-mentioned patch, is black or smoky brown.
This bird nests in colonies in the verandahs of houses and inside deserted buildings. The nest is a cup-shaped structure, usually built under an eave in the angle which a roof-beam makes with the wall. Thus the swift finds, ready-made, a roof and a couple of walls, and has merely to add the floor and remaining walls, in one of which it leaves a hole by way of entrance to the nursery. Thus the swift reverses the usual order of things, which is to erect a nest on some foundation such as a branch or ledge.
As we have seen, all four toes of the swift are forwardly directed and each is terminated by a sharp hook-like claw. Thus the swift is able to cling with ease to such a vertical surface as that of a wall, and is therefore quite independent of any ledge or perch. The nest is a conglomeration of grass, straw, and feathers, which are made to adhere to one another, and to the building to which the nest is attached, by the cement-like saliva of the bird.
Some species of swift build their homes entirely of their glutinous saliva, and so manufacture "edible birds' nests." The Indian swift, however, utilises all manner of material by way of economising its saliva.
Nest building is a slow process. Each tiny piece of material has to be separately stuck on to the structure, and the saliva, which is, of course, liquid when first secreted, takes about five minutes to dry. During the whole of this time the bird remains motionless, holding in situ whatever it is adding to the structure.
I once timed a pair of swifts at work, and found that on an average they took forty-five minutes in bringing each new piece of material. Much of this time was undoubtedly spent in seeking for food, for so active a bird as the swift must have an enormous appetite, and, as it feeds on the minutest of insects, must consume thousands of them in the course of the day, each of which has to be caught separately. But, even allowing for this, the rate at which the material is added is very slow. Some naturalists declare that the swift is unable to pick anything off the ground. If this be so, the labour of obtaining material must be great, for the creature must fly about until it espies a feather or piece of straw floating in the air.
I am not yet in a position to say whether it is really impossible for the bird to pick anything from off the ground. I have never seen it do so, and it is a fact that the birds will, when building, eagerly seize anything floating in the air. On the other hand, the helplessness of the swift when placed upon the ground has been much exaggerated. It is said that the bird, if put upon a flat surface, is unable to rise and will remain' there until it dies. Quite recently some Indian swifts were brought to me and I placed one of them on my desk. In less than twenty seconds the bird was flying about in the room. Then, again, the grasping powers of its hook-like claws have been somewhat magnified. The bird in question made several unsuccessful attempts to cling on to the whitewashed wall, and eventually fell to the floor, where it was seized and then liberated in the open. It flew off none the worse for its adventure. Nevertheless, its claws are very sharp; the bird in question stuck them quite unpleasantly into me when I held it. A swift can certainly cling to any vertical surface that is the least rough.
Unlike most birds, swifts use their nests as houses and sleep in them at night. One frequently hears issuing from the rafters in the dead of night the piercing scream so characteristic of swifts. This disposes of the silly story, so prevalent, that at evening time the swifts mount into the higher layers of the atmosphere and there sleep on the wing.
In conclusion, I must mention the characteristic flight of swifts just before sundown. The birds close the day in what has been called " a jubilant rout" ; as if they had not already taken sufficient exercise, they fly at a breakneck pace round about the building in which their nests are placed, dodging in and out of the pillars of the verandah, and fill the air with their shivering screams. This seems to be a characteristic of swifts wherever they are found.