Incubation is performed mostly, if not entirely, by the male. I flushed females off nests on two occasions, but in one case the full complement of eggs was not yet laid, and in the other I think they were only newly laid. The ground color of the eggs varied from stone to olive, and in one nest all four eggs were remarkably rotund. They take some 18 days to hatch, and only one brood is hatched in the season, though if the first sitting is destroyed the bird will lay again. The nestlings, although they can not fly for some days, are wonderfully precocious and can swim immediately. Their beautiful golden downy plumage becomes paler and paler, even after the first 24 hours. When the nest contains eggs the female bird shows the greatest anxiety. She can be seen swimming about in the pools; or, rising without any splash, flying up and down quite close to one, uttering a low cry of "_plip, plip_," varied by a hoarse "_chiss-ick_." This cry warns the male, which never flies off the nest, but always creeps through the grass and rushes, to some pool, near one of which the nest is invariably placed. Here he will soon be joined by the female, and they will swim about trying to hide their anxiety by preening their feathers or pretending to feed. Some observers have said that the young do not take to the water until they are fully fledged, but Mr. Hersey's notes say that: "They run lightly over the beaten down masses of grass around the tundra ponds and when they know they are discovered take to the water and swim as well as their parents." Doctor Nelson (1887) writes: Fresh eggs are rarely found after June 20th, and by the middle to 20th of July the young are fledged and on the wing. By the 12th to 15th of July a few of the ashy feathers of the autumnal plumage appear, and soon after old and young begin to gather in parties of from five to a hundred or more, and seek the edges of large ponds and flats or the muddy parts of the coast and borders of tide creeks. During August and September they are found on the bays, and the last are seen about the last of September or first of October.