. Bulletin of the Department of Agriculture. Agriculture; Agriculture. UNITED STATES DEPARTMENT OF AGRICULTURE BULLETIN No. 185 Contribution from the Bureau of Biological Survey HENRY W. HENSHAW, Chief Washington, D. C. April 17,1915 BIRD MIGRATION By WELLS W. COOKE, Assistant Biologist CONTENTS Introduction 1 Causes of Migration 2 Relation of Migration to Weather ... 4 Day and Night Migrants 5 Distance of Migration 7 Routes of Migration 11 Direct and Circuitous Migration Routes .' 19 Eccentric Migration Routes ,21 Wide and Narrow Migration Routes . ' 23 Slow and Rapid Migration 25 How Bi
. Bulletin of the Department of Agriculture. Agriculture; Agriculture. UNITED STATES DEPARTMENT OF AGRICULTURE BULLETIN No. 185 Contribution from the Bureau of Biological Survey HENRY W. HENSHAW, Chief Washington, D. C. April 17,1915 BIRD MIGRATION By WELLS W. COOKE, Assistant Biologist CONTENTS Introduction 1 Causes of Migration 2 Relation of Migration to Weather ... 4 Day and Night Migrants 5 Distance of Migration 7 Routes of Migration 11 Direct and Circuitous Migration Routes .' 19 Eccentric Migration Routes ,21 Wide and Narrow Migration Routes . ' 23 Slow and Rapid Migration 25 How Birds Find Their Way ...... 27 Page Migration and Molting 31 Casualties During Migration 31 Are Birds Exhausted by Long Flight ? . 33 Evolution of Migration Routes .... 35 Normal and Abnormal Migration ... 37 Relative Position During Migration . 40 Relation Between Migration and Tem- perature 41 Variations in Speed of Migration ... 43 The Unknown 47. WASHINGTON GOVERNMENT PRINTING OFFICE 1915. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original United States. Dept. of Agriculture. [Washington, D. C. ?] : The Dept. : Supt. of Docs. , G. P. O.
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