Diving, in water-birds, is also an instinctive mode of behaviour; and this is obviously a more difficult procedure than swimming, one further removed from reflex action. And careful observations have placed beyond question the fact that flight is also instinctive. A swallow, for example, taken from the nest under conditions which made it practically certain that it had never yet taken wing, exhibited guided flight, and attempted to alight on a suitable ledge. Of course flight is generally a deferred instinct, and is not performed until the wings have reached a suitable state of development. An instinctive response, which may perhaps be regarded as one of its initial stages, is seen in quite young chicks. If placed in a basket, and rapidly lowered therein through a foot or two, the chick will extend its skinny and scarcely feathered wings. But though, from the usual conditions of development, flight in birds is a deferred instinct, yet in exceptional cases it may be connate. The mound-builders (_Megapodes_) of the Australian region are hatched from large eggs in warm earth or sand, and are not tended by the parents. So well fledged are these birds that they can fly the day they emerge from the egg. Dr. Worcester, while digging in one of their mounds, made an unsuccessful attempt to seize one which was newly hatched; but it flew several rods into thick brush, and this notwithstanding the fact that it had probably never before seen the light of day.
[Illustration: FIG. 16.--Nestling Megapode, to show the well-developed wings. (From Dr. R. Bowdler Sharpe’s “Wonders of the Bird World.”)]
It must not be supposed that, in adducing flight as an example of instinctive behaviour in birds, we are contending that it is this and nothing more throughout life. The inference to be drawn from the facts of observation is rather that instinct provides a general ground plan of behaviour which intelligent acquisition, by enforcing here and checking there, perfects and guides to finer issues. Few would contend that the consummate skill evinced in fully developed flight at its best, the hurtling swoop of the falcon, the hovering of the kestrel, the wheeling of swifts in the summer air, the rapid dart and sudden poise of the humming bird, the easy sweep of the sea-gull, the downward glide of the stork--that these are, in all their exquisite perfection, instinctive. A rough but sufficient outline of action is hereditary; but the manifold graces and delicacies of perfected flight are due to intelligent skill begotten of practice and experience.