Page:Popular Science Monthly Volume 76.djvu/539

Rh bodies. Under such circumstances a slight error in muscular coordination would be fatal, and I have found fully grown and presumably young birds lying dead beneath such openings, where it was evident from the wounds received that death was accidental, and due to lack of precision in flight. The common swift also moves with astounding rapidity, as if heedless of consequences, but usually avoids every obstacle in its path, even in waning light. It gathers the materials for its twig nests while darting through the branches of a tree, with barely a pause, as it bends to seize in its bill the twig, which is snapped off by the momentum thus gained. Yet mistakes are sometimes made even by the master swift, and I have known a case where a bird of this kind, and possibly a young one, impaled itself on the sharp point of a lightning rod.

The toothed birds of the Cretaceous period, of which Hesperornis is a type, are known to have possessed a brain more nearly approaching that of the reptiles in form, with large olfactory lobes. It thus seems evident that the olfactory sense has lapsed and become rudimentary in most modern birds. Edinger, however, maintains that since birds possess true, though small olfactory lobes, they must smell, but behavior seems to afford the better criterion in such a case. Whatever the advocates of the eye and the nose may have to offer in the future in regard to the habits of buzzards and other old and new world scavengers, repeated experiment has convinced me that the common birds of the country, can not detect their young at a distance of three feet, unless they either see or hear them. In fact, all of the close-at-hand, "as-near-as-you-hold-a-book-to-read" observation, carried on for the past ten years, some of which is to follow, has been conditioned upon the extremely feeble development, if not total lack of this sense.

The instincts of birds may be classed in a general way as (1) continuous instincts, which are needed for the preservation of the individual, such as preying, flight, concealment and fear, however subject to modification through experience, and (2) the cyclical instincts, which are necessary for the preservation of the race.

By cyclical instincts we mean those discontinuous, recurrent tendencies to action which are serial in form, and which together characterize the reproductive cycle. They may be called, with some allowance, the parental instincts, it being understood that this epithet is used in a descriptive sense, and that there is no one kind of reaction to which the term is specially applied. These instincts recur with clock-like regularity in the spring and summer in the northern hemisphere, and are subject to repetition, more or less complete, within the breeding season of certain species or individuals.