On September 16, 1896, after a period of very stormy wet weather, I saw a great migration of swallows down the Thames. It was a dark, dripping evening, and the thick osier bed on Chiswick Eyot was covered with wet leaf. Between five and six o'clock immense flights of swallows and martins suddenly appeared above the eyot, arriving, not in hundreds, but in thousands and tens of thousands. The air was thick with them, and their numbers increased from minute to minute. Part drifted above, in clouds, twisting round like soot in a smoke-wreath. Thousands kept sweeping just over the tops of the willows, skimming so thickly that the sky-line was almost blotted out for the height of from three to four feet. The quarter from which these armies of swallows came was at first undiscoverable. They might have been hatched, like gnats, from the river.

In time I discovered whence they came. They were literally "dropping from the sky." The flocks were travelling at a height at which they were quite invisible in the cloudy air, and from minute to minute they kept dropping down into sight, and so perpendicularly to the very surface of the river or of the eyot. One of these flocks dropped from the invisible regions to the lawn on the river bank on which I stood. Without exaggeration I may say that I saw them fall from the sky, for I was looking upwards, and saw them when first visible as descending specks. The plunge was perpendicular till within ten yards of the ground. Soon the high-flying crowds of birds drew down, and swept for a few minutes low over the willows, from end to end of the eyot, with a sound like the rush of water in a hydraulic pipe. Then by a common impulse the whole mass settled down from end to end of the island, upon the osiers. Those in the centre of the eyot were black with swallows - like the black blight on beans.

Next morning, at 6.30 a.m., every swallow was gone. In half an hour's watching not a bird was seen. Whether they went on during the night, or started at dawn, I know not. Probably the latter, for Gilbert White once found a heath covered with such a flock of migrating swallows, which did not leave till the sun dispelled the mists.

The migration routes of birds follow river valleys, when these are conveniently in line with the course they wish to take. There is far more food along a river than elsewhere, and this is a consideration, for most birds, in spite of the wonderful stories of thousand-mile flights, prefer to rest and feed when making long migrations, and also those short shifts of locality which temporary hard weather causes. A friend just back from Khartoum tells me that he saw the storks descending from vast heights to rest at night on the Nile sandbanks, and saw their departing flight early in the morning, these birds being in flocks of hundreds and thousands.

By watching the river carefully for many years I have noticed that it is a regular migration route for several species besides swallows. The first to begin the "trek" down the river are the early broods of water-wagtails, both yellow and pied. They turn up in small flocks so early in the summer that one might almost doubt if they could fly well enough to take care of themselves. On June 26th last summer nearly forty were flying about in the evening, and went across to roost on the eyot. Later numbers of blackbirds arrive, also moving down the river. Sand-martins, when beginning the migration, travel down the Thames in small flocks, and sleep each night in different osier beds. How many stages they make when "going easy" down the river no one knows. But I have seen the flocks come along just before dusk, straight down stream, and then dropping into an osier bed.

In the second week of September there is usually an immense migration of house-martins and swallows down the river. I have already described what I once saw on a migration night on Chiswick Eyot. Sometimes they go on past London, and find themselves near Thames mouth with no osier beds or shelter of any kind. Then they settle on ships. I was told that one morning the craft lying in Hole Haven off Canvey Island were covered with swallows, all too numb to move, but that when the sun came out the greater number flew away towards the sea. The same thing happened on the windmill at Cley, in Norfolk, a famous starting and alighting place for birds. Moorhens evidently migrate up or down the river in spring and autumn, and occasionally dabchicks; otherwise their sudden appearance and disappearance on the eyot could not be accounted for. Snipe follow the Thames up the valley. Formerly Chiswick Eyot was their first alighting place when east winds were blowing, after the fatigue of crossing London; and persons still living used to go out and shoot them. A friend of mine, whose family has resided in Chiswick for several generations, used to go down the outside of the eyot and kill snipe, and also kill teal and duck in the stream which runs from Chiswick House into the river. Another friend broke a young pointer to partridges on the market garden between Barnes Bridge and Chiswick.

Probably a number of the warblers also use the river as a migration road, though I only notice them in spring. But as I am never here in early September possibly many pass without being noticed. Also they are silent in autumn, whereas in spring they sing, a little, but enough to show that they are there.

Among the birds of this kind which pass up the river, but of which only a few pairs stay to breed on the eyot, are whitethroats, blackcaps, chiff-chaffs, and, I believe, nightingales. One beautiful early morning in spring I could not believe my ears, but I heard a nightingale in a bush by the side of the garden overhanging the river. It sang for about an hour, "practising" as nightingales do. Another person in a house near also heard it, and was equally astonished. It probably passed on, for next day it was inaudible.

In hard weather a migration of a different kind takes place down the river towards the sea. These birds are recruited from the ranks of the birds that stay, with some foreign winter visitors also. They pass down the river feeding on the mud and among the stones at ebb tide. Among those I have seen are flocks of starlings and scattered birds, mainly redwings, thrushes, blackbirds, and occasionally robins. Sandpipers also migrate up the Thames in spring, and down it in autumn.