Читать книгу Migration of Birds (1979) онлайн

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Before we discuss the many intricacies of how, when, and where birds migrate, one should have a general idea of how migration data are collected and what methods are currently being used to increase our knowledge. Since this publication first appeared in 1935, many new procedures have been used in the study of bird migration. One of these, radar, has been an invaluable adaptation of a technique developed for a quite different, but related, purpose.

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The oldest, simplest, and most frequently used method of studying migration is by direct observation. Size, color, song, and flight of different species all aid the amateur as well as the professional in determining when birds are migrating. Studies begun by Wells W. Cooke and his collaborators (Cooke 1888-1915) and continued by his successors in the U.S. Bureau of Biological Survey (later U.S. Fish and Wildlife Service) were of particular importance in the earlier years of these investigations in North America. Some of the largest and most interesting routes and patterns were sorted out by tediously compiling and comparing literally thousands of observations on whether a species was or was not seen in a given locality at a particular time of the year. More recently, "The Changing Seasons" reports by many amateur bird observers in Audubon Field Notes (now American Birds) have been a most important source of information on direct observation of migration. In the aggregate, direct observation has contributed much to our knowledge of migration, but, as will be pointed out in other sections, until a few years ago, observers were not aware of some of the biases in this technique.