

1 — ]TI 



CIRCULAR No. 428 MAY 1937 



UNITED STATES DEPARTMENT OF AGRICULTURE 



WASHINGTON, D.C. 



FLIGHT SPEED OF BIRDS 



By May Thacher Cooke, junior biologist, Section of Distribution and Migration 

 of Birds, Division of Wildlife Research, Bureau of Biological Survey 



CONTENTS 



Page 



Introduction 1 



Estimated speeds 1 



Measured speeds 2 



Variations in speed 2 



Effect of wings and weight 3 



Variations in speed— Continued. 



Influence of wind. 4 



Table of speeds 5 



Bibliography 10 



INTRODUCTION 



A bird's power of flight is one of its most fascinating characteristics 

 and one that from the earliest times has stirred man's imagination 

 and aroused his envy. One of the writers of the Book of Proverbs 

 found "the way of an eagle in the air" too wonderful for his compre- 

 hension. Today, by calling mechanics to his aid, man has achieved 

 the power to travel "as the crow flies"; and although the aviator is 

 still much less independent in the air than the birds he seeks to 

 emulate, we are indebted to him, nevertheless, for much information 

 regarding the flight of birds. 



Three phases of bird flight have been the subject of much conjec- 

 ture and investigation, namely, the speed of flight, the altitude of the 

 migratory flights, and, especially in recent years, the mechanics or 

 aeronautics of flight. It is the purpose of the present circular to deal 

 principally with the first, speed of flight, though reference is made 

 to the other two phases in the text and titles of articles dealing with 

 them are included in the bibliography, which gives also the authority 

 for all records of speed given in the table (p. 6) . 



ESTIMATED SPEEDS 



Many years ago Gatke (27), l reporting his observations of migratory 

 birds on the island of Helgoland in the North Sea, expressed his 

 belief that even small birds in migration travel at speeds as great as 

 3 or 4 miles a minute. His figures were based on the false premises 

 that birds made the trip from winter to summer home, or the reverse, 

 in a single flight of a few hours and that they were able to do this by 

 flying thousands of feet, even several miles, above the earth, where 

 the rarefied air offered less resistance. Aviators now tell us that at 

 great altitudes the lessened buoyancy of the air makes flight more 

 instead of less difficult. 



i Italic numbers in parentheses refer to the bibliography, p. 10, 

 121989°— 37 1 



