Since the previous edition, tremendous progress has been made in researching and understanding bird migration; along with this increased effort has come a substantial increase in the literature devoted to the subject. Emphasis was given to reviewing literature pertaining to migration studies conducted in North America after 1950, but a number of examples from the European literature have been included to emphasize similarities and differences in migration throughout the world. Because extensive author citations tend to disrupt the flow of thought, they were kept to a minimum in the text. However, this publication is essentially a review of the literature on the subject as it existed in the early 1970's, and a rather extensive bibliography has been included to cover all the papers quoted in the text as well as the many used but not specifically cited. The bibliography, then, is primarily intended for those interested in pursuing the subject further. =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.