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Migration of Birds

Introduction


The changing picture of bird populations throughout the year intrigues those who are observant and who wish to know the source and destination of these birds. Birds are the most mobile creatures on Earth. Even man with his many vehicles of locomotion does not equal some birds in mobility. No human population moves each year as far as from the Arctic to the Antarctic and return. Yet the Arctic terns do-and without the aid of aircraft or compass.

Birds are adapted in their body structure, as no other creatures, to life in the air. Their wings, tails, hollow bones, and internal air sacs all contribute to this great faculty. These adaptations make it possible for birds to seek out environments most favorable to their needs at different times of the year. This results in the marvelous phenomenon we know as migration the regular, seasonal movement of entire populations of birds from one geographic location to another.

Throughout the ages, migratory birds have been important as a source of food after a lean winter and as the harbinger of a change in season. The arrival of certain species has been heralded with appropriate ceremonies in many lands; among the Eskimos and other tribes, the phenomenon to this day is the accepted sign of the imminence of spring, of warmer weather, and a change from winter food shortages. The pioneer fur traders in Alaska and Canada offered rewards to the Indian or Eskimo who saw the first flight of geese in the spring, and all joined in jubilant welcome to the newcomers.

As the North American Continent became more thickly settled, the large flocks of ducks and geese, rails, doves, and woodcock that always had been hunted for food became objects of the enthusiastic attention of an increasing army of sportsmen. Most of the nongame species were found to be valuable also as allies of the farmer in his never-ending warfare against insect pests. All species have been of ever-increasing recreational and esthetic value for untold numbers of people who enjoy watching birds. We began to realize our migratory bird resource was an international legacy (that cannot be managed alone by one state or country) and all nations were responsible for its well-being. The need for laws protecting game and nongame birds, as well as the necessity to regulate the hunting of diminishing game species, followed as a natural course. In the management of this wildlife resource, it has become obvious that continuous studies must be made of the species' habits, environmental needs, and travels. In the United States, the Department of the Interior recognizes the value of this resource and is devoted to programs that will ensure its preservation and wise use. Hence bird investigations are made by the U.S. Fish and Wildlife Service, an arm of the Interior Department, charged by Congress under the Migratory Bird Treaty Act, with the duty of protecting those species that in their yearly journeys, pass back and forth between the United States and other countries.

For more than three-quarters of a century the Fish and Wildlife Service and its predecessor, the Biological Survey, have been collecting data on the important details of bird migration. Scientists have gathered information concerning the distribution and seasonal movements of many species throughout the New World, from the Canadian archipelago south to the Argentine pampas. Supplementing these investigations is the work of hundreds of U.S. and Canadian university personnel and volunteer birdwatchers, who report on the migrations and status of birds as observed in their respective localitites; while others place numbered bands on the legs of birds to determine their movements from one place to another. These data, stored in field notes, computer cards, scientific journals, and on magnetic tape constitute an enormous reservoir of information pertaining to the distribution and movements of North American birds. It is the purpose of this publication to summarize these data and present the more important facts about that little understood but universally fascinating subject of bird migration. The U.S. Fish and Wildlife Service is grateful to the many persons who have contributed their knowledge so that other people, be they bird study classes, conservation organizations, or just individuals interested in the welfare of the birds, may understand and enjoy this precious resource as well as preserve it for generations to come.


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