After London by Richard Jefferies

This little circumstance of the mallards always flying over him and away behind, when flushed, presently made Felix speculate on the cause, and he kept a closer watch. He now saw (what had, indeed, been going on for some time) that there was a ceaseless stream of waterfowl, mallards, ducks, coots, moorhens, and lesser grebes coming towards him, swimming to the westward. As they met him they parted and let him through, or rose and went over. Next he noticed that the small birds on the islands were also travelling in the same direction, that is against the wind. They did not seem in any haste, but flitted from islet to islet, bush to tree, feeding and gossiping as they went; still the movement was distinct.

Finches, linnets, blackbirds, thrushes, wrens, and whitethroats, and many others, all passed him, and he could see the same thing going on to his right and left. Felix became much interested in this migration, all the more singular as it was the nesting-time, and hundreds of these birds must have left their nests with eggs or young behind them. Nothing that he could think of offered an adequate explanation. He imagined he saw shoals of fishes going the same way, but the surface of the water being ruffled, and the canoe sailing rapidly, he could not be certain. About an hour after he first observed the migration the stream of birds ceased suddenly.