“One swallow does not make a summer”, but tens of thousands do, and now that they are here in force we can safely say that summer, in its broadest sense, has arrived at last.
The swallow is not the first of its family to appear: the sand martin is usually the earliest. The swallow itself is next, and then the house martin. Finally, on or about 23 April, comes the swift – which is of course not a member of the swallow family at all.
The four birds each catch their insect food in flight, and although superficially similar, are not difficult to tell apart. The swift is wholly dark except for a pale patch on the chin, and has very long, scimitar-like wings and a short tail only moderately forked. The three hirundines also have forked tails, but their wings are shorter, and they are all white or whitish below. The sand martin has earth-brown upper-parts, the house martin and swallow dark blue, but the house martin has a distinctive white rump by which it can be told even at a great distance.
It would be hard to think of a more pleasing or attractive bird than the swallow, or of one which adds more charm to the countryside. Its generally low, graceful flight is marvellously smooth and controlled, swooping over a cornfield, endlessly quartering the broad expanses of pasture where sheep or cattle are grazing, by whim turning to left or right when coming to an obstacle, or, inches from the turf, skimming among the boles of standing trees.
The swallow is such an exact and delicate artist of flight that it drinks on the wing, dipping its lower mandible into the surface film of the river to scoop up a little water. When it wishes to bathe, it descends an inch further, douses itself, and then rises to complete its toilet in the air. It rarely settles on the ground, except to collect particles of gravel for its gizzard or materials for its nest, and almost all of its food – mainly gnats, flies, and small beetles – is taken on the wing.
The elegance of the swallow’s flight is matched by the beauty and rightness of its plumage. The dark blue upper parts have a metallic sheen, varying almost to dark green depending on the angle of the light. In the adult male especially, the outer tail feathers are attenuated into streamers which are can be fully two inches longer than the next feathers in. The tail feathers are not blue, but a deep bottle-green, marked on their inner webs with spots of white. Below, the swallow is buff on belly and underwings, with a metallic blue band across the chest and, setting off all the rest of the colours, a dark chestnut throat and face.
The female is normally rather whiter below, with shorter streamers. She and her mate always return, if possible, to the same nest-site year after year. The favourite place is a ledge or rafter in a barn or outhouse, although at one time the deep recesses of large, old-fashioned chimneys were much used.
Before the widespread construction of buildings, the swallow must have been quite a rare bird in England, for its presumed natural nesting sites – caves and sheltered hollows in rock-faces – are few and far between. Since the time of the Romans, it has become completely adapted to using human “caves” for its nests, and is now one of the few species, like the house sparrow, which is more at home with man than in the wilderness.
The nest itself is made of mud, collected from puddles and riverbanks and reinforced with shreds of grass. It in is the shape of half a saucer, and is lined with the softest bents and feathers (the latter often collected in flight).
The eggs, normally 4-6, are white, blotched and speckled with russet and grey, and are incubated mainly or completely by the female. They take a fortnight or so to hatch. Both parents feed the young, which must be a daunting task, bearing in mind the slightness of each catch. This could be one of the reasons why the young take a comparatively long time – about three weeks – to leave the nest. As soon as they can fly and feed themselves, the parents begin another brood, and there may even be a third.
So strong is the urge to depart in the autumn that when, because of bad weather or through some other delay, this third brood is late in the year, the nestlings may be abandoned and left to starve.
For the early naturalists the swallow was the summer visitor which most exercised their curiosity. In one camp were those who believed, as the Greeks had done, that swallows and martins spent the winter either in the mud at the bottom of ponds, or in hibernation in a hollow tree-trunk or cave; in the other were those who believed in migration.
The advent of modern travel and bird-marking with leg rings settled the matter, and now we know that the swallows which nest here winter as far south as the Cape.
There they remain until late February or March, when, covering a hundred miles or more each day, they begin to make their way northwards. Once over England, the swallow migration progresses in a broad front, with a tendency to follow river-valleys where these run in the right direction.
And finally, within a few days on either side of 6 April, the swallows again return and bring their delightful presence to make us yet another summer.