"flapping," and consists in simply breaking the force of a descent; this is followed by a more effectual use of the wings, and horizontal progression, and it is some time subsequent to this that the young birds attain to the power of upward flight. This holds good of a considerable number of species, studied with special reference to their flight, as the robin, the wood-thrush, cedar-bird, cat-bird, pewee, and indigo-bird.
It is doubtful if young birds, while yet in their nests, are conscious of the use to be made of their wings. After long-continued experimenting, I find they make no use of them, in endeavoring to escape, but trust to their legs entirely, if removed from the nest, or defend themselves by pecking at the intruder. When a sufficient growth of feather has been obtained, the parent-birds, directly and indirectly, instruct them; or, perhaps more properly, force them to use their wings. So, at least, I can only interpret certain habitual actions of the parent-birds with reference to their newly-fledged young.
As an instance I will quote from my field-notes, with reference to the indigo-bird: "June 23, 1873. Found a nest of this species in a dense thicket of blackberry, and, curiously enough, within just seven paces of the railroad-track. The young birds were just ready to leave the nest. I visited the nest the next day, and saw on my approach one of the four young birds sitting on a brier-stem, about a yard from the nest. Taking a favorable position, I continued to watch the birds closely, as they were very restless and noisy. Evidently something unusual had occurred or was occurring. In a few moments I saw the hen-bird go to the nest and push one of the young birds out of the nest. It forced it from the edge of the nest, to which it clung with its feet. Once free, the little fellow struggled to keep itself up, throwing up its wings, as a child would straighten out its arms when falling. This was the initial movement that developed into flight. All of the young birds were thus forced from the nest, and I am satisfied from no outside cause, as, for the three following evenings, the young returned to the nest to roost. I spent several hours watching this brood and their parents, and the whole time was occupied, except short intervals when they were fed, in forcing the young birds from point to point, but ever keeping them from the railroad-track, over which trains passed frequently. Two days from leaving the nest they could fly six or eight yards, but always from a higher to a lower perch, and regained the more elevated branches by very short, 'jumping' flights, with a laborious flapping of the wings; but on the fifth day they could follow their parents almost any distance, and execute an upward flight with apparently the same ease. Examination of the wing-feathers on the 30th of June, as compared with a week previous, showed so slight gain in the growth of the feathers, that I believe nothing in the increased flight-power was due to their being now better fledged."