Incubation lasts about a month. The young ones are then hatched, all generally bursting the egg on the same day. They are covered with a close yellow down, and are quite alert when they leave the shell; and their mother soon leads them down to the water, encouraging them by her example to enter it. They do not return to the nest. At night their mother covers them under her wings, and at first feeds them with the small flies that come within her reach. The ducklings, although they soon learn to swim, are unable to fly till after the expiration of three months; after that lapse of time wing-feathers are developed sufficiently to enable them to take flight. But they are always alert and active on the water, diving and remaining under it for many minutes with nothing but the bill above the surface. When danger approaches, the mother utters a peculiar cry, and the young ones immediately conceal themselves. In a ditch full of water, Mr. McGillivray once came upon a whole brood of half-grown ducklings which disappeared in a moment; and although he searched everywhere for them, he did not succeed in finding a single one. When the Duck perceives the great Black-backed Gull, the ruthless enemy of her race, she beats the water with her wings as if to attract the attention of the aggressor. On his approach she darts at him with so much vigour that she compels him to retire, shamefully beaten. Audubon relates a remarkable instance of maternal affection in this bird. The American naturalist had found in the woods a female of this species at the head of her young brood. As he approached, he noticed that her feathers became erect, and that she hissed with a threatening gesture, after the manner of Geese. In the meantime, the ducklings made off in all directions. His Dog, which was perfectly trained, brought the little creatures to him, one by one, without doing them the least injury. But in all his proceedings he was watched by the mother, who kept passing and repassing in front of him, as if to distract his attention. When the ducklings were all safe in the game-bag, in which they struggled and cried out, the mother came with a sad and troubled air, and placed herself close to the sportsman, as if unable to suppress her despair. Audubon, seeing her grovelling almost under his feet, was filled with pity, and restored her little family before leaving the spot. "When I turned round to watch her," adds the naturalist, "I really fancied I could detect an expression of gratitude in her eyes; and I experienced at that moment one of the most vivid sensations of pleasure I have ever enjoyed."