Birds of America (Classic Reprint)
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| Partner: | buecher.de |
| Hersteller: | Forgotten Books (Pearson, T. Gilbert) |
| Stand: | 2015-08-04 03:50:33 |
Produktbeschreibung
Excerpt from Birds of America The mystery of bird migration has proved a fascinating subject for speculation and study from earliest times. Long ago it was noticed that birds disappeared in fall and reappeared in spring, but, not knowing where they spent the intervening period, many fanciful theories were advanced to account for their disappearance, as hibernation in hollow trees or in the mud of streams or ponds. With later years, however, has come a fuller knowledge of migration, especially of the particular region in which each species passes the cold season, and more definite information in regard to the routes followed in the spring and fall journeys. But fuller knowledge has served to increase rather than to lessen interest in the subject. More persons to-day are watching birds and noting their times of arrival and departure than ever before. A knowledge of the times of migration of birds is essential as a basis for intelligent study of their economic relations and is equally necessary in formulating proper legislation for bird protection - two subjects which form important parts of the work of the United States Biological Survey. For more than 2, 000 years the phenomena of bird migration have been noted; but while the extent and course of the routes traversed have of late become better known, no conclusive answer has been found to the question. Why do North American birds migrate? Two different and indeed diametrically opposite theories have been advanced to account for the beginnings of these migrations. According to the more commonly accepted theory, ages ago the United States and Canada swarmed with non-migratory bird life, long before the Arctic ice fields advancing south during the glacial era rendered uninhabitable the northern half of the continent. The birds´ love of home influenced them to remain near the nesting site until the approaching ice began for the first time to produce a winter - that is, a period of inclement weather which so reduced the food supply as to compel the birds to move or to starve. As the ice approached very gradually, now and then receding, these enforced retreats and absences - at first only a short distance and for a brief time - increased both in distance and in duration until migration became an integral part of the very being of the bird. In other words, the formation of the habit of migration took place at the same time that changing seasons in the year replaced the continuous semi-tropical conditions of the preglacial eras. As the ice advanced southward the swing to the north in the spring migration was continually shortened and the fall retreat to a suitable winter home correspondingly lengthened, until during the height of the glacial period birds were for the most part confined to Middle and South America. But the habit of migration had been formed, and when the ice receded toward its present position the birds followed it northward and in time established their present long and diversified migration routes. Those who thus argue that love of birthplace is the actuating impulse to spring migration call attention to the seeming impatience of the earliest migrants. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.
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