These insular colonies, however, not only throw much light on certain existing phases of bird migration, but they also furnish us with a clew to the origin of migration itself. This is especially true of those species whose lives are passed in the tropics or subtropics, and which we are accustomed to class as nonmigratory or as “permanent residents,” but which are as regularly migratory, in the real meaning of the word, as if they summered within the arctic circle and wintered south of the equator. Their movements are apparently in no way influenced by climate nor, at this season, are they governed by the food supply, but prompted solely by the annually recurring physiological change which fits both sexes for reproduction, they repair to a certain islet, perhaps in the heart of their range, with the one object of finding a suitable nesting site in which their eggs may be laid and young reared in safety; and this object accomplished, they desert the locality, where they may be unknown until the following spring. Divested, therefore, of the complications which ensue when in studying the migration of birds the questions of food and climate must be considered, we have here the problem reduced to its simplest terms; and in the desire for seclusion during the breeding season which induces birds to conceal their nests, if possible perhaps near by, but if necessary after a journey of varying length undertaken especially for the purpose, we have a good and sufficient cause for the origin of bird migration. An attempt to explain the present manifestation of the migratory movement involves a study of the climatic changes to which our globe has been subjected. No doubt many birds controlled by “heredity of habit” make semiannual journeys which at one time were necessary, but under existing circumstances are no longer required. Why, for example, should the Bobolink winter south of the Amazon, while its ally, the Red-winged Blackbird (_Agelaius phœniceus_), does not leave the eastern United States? I have, however, no intention of writing an essay on bird migration, and these thoughts are presented merely as preliminary to a study of the life of Pelican Island, of a visit to which they are in part the outcome. Pelican Island is situated midway between the northern and southern extremities of Indian River, near the eastern shore of a key which here makes the river about three miles wide. It is triangular in shape and contains about three acres of ground, on which grow a few black mangroves, a cabbage palm or two, and great patches of grass; but at least one fourth of its surface is bare ground. On one of the islands of the near-by Narrows a few pairs of Brown Pelicans are said to have nested, but, with this exception, Pelican Island doubtless forms the nesting ground of all the Pelicans of Indian River.