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.
There were no waterfowls in the water, and no finches in the bushes.
They had evidently all passed.

Those in the van of the migratory army were no doubt scattered and thinly distributed, so that he had been meeting the flocks a long while before he suspected it.

The nearer he approached their centre the thicker they became, and on getting through that he found a solitude.

The weeds were thicker than ever, so that he had constantly to edge away from where he supposed the mainland to lie.
But there were no waterfowls and no birds on the islets.