INTRODUCTION 



Biological problems can be approached from a 

 number of angles. The specialist views them 

 through the glasses that he habitually wears, with 

 his special interests magnified and in the foreground, 

 a profitable proceeding but likely to suffer from dis- 

 torted perspective. The gathering up of the view- 

 points of the various specialists is a certain way 

 of restoring proportions and arriving at a compre- 

 hensive and at the same time an analytical picture 

 of the whole. 



The migrations of birds have been a subject of 

 interest for centuries. They have been examined 

 from two avenues of approach. One of them has 

 been worn wide and smooth: the other remains 

 almost untrodden. Field observations and specula- 

 tions based thereon exist in sufficient volume to fill 

 a library, but few and far between are the attempts 

 of the technically trained biologist — the anatomist, 

 biochemist, biophysicist, physiologist, etc. — to 

 apply his special knowledge to the problem. 



It requires little imagination to see that both are 

 crucial aspects of the subject. An illustration will 

 make this clearer. Every bird student is familiar 



