Transcriber's Note Emphasized text is denoted by _Italics_ and =Bold=. [Illustration] MIGRATION of BIRDS [Illustration] CIRCULAR 16 FISH AND WILDLIFE SERVICE UNITED STATES DEPARTMENT OF THE INTERIOR MIGRATION of BIRDS [Illustration] By FREDERICK C. LINCOLN _Biologist_ Illustrated by BOB MINES CIRCULAR 16 UNITED STATES DEPARTMENT OF THE INTERIOR, Oscar L. Chapman, _Secretary_ FISH AND WILDLIFE SERVICE, Albert M. Day, _Director_ [Illustration] UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1950 For sale by the Superintendent of Documents, Washington 25, D. C. Price 30 cents Contents Page The mystery of migration 4 Advantages of migration 6 The origin of migration 7 Northern ancestral home theory 8 Southern ancestral home theory 8 Theory of photoperiodism 9 Theory of continental drift 11 When birds migrate 11 Movements of species and groups 12 Nocturnal and diurnal migration 15 How birds migrate 18 Speed of flight and speed of migration 18 Altitude at which birds travel 26 Orientation 28 Segregation during migration 31 Where birds migrate 34 Short and undetermined migrations 34 Variable migrations within species 35 Fall flights not far south of breeding ranges 37 Long-distance migrations 38 Routes of migration 41 Wide and narrow migration lanes 42 The fly ways 46 Atlantic oceanic route 48 Atlantic coast route and tributaries 53 Mackenzie Valley--Great Lakes--Mississippi Valley Route and tributaries 60 Great Plains--Rocky Mountain routes 62 Pacific coast route 63 Pacific oceanic route 66 Arctic routes 68