PREFACE 



The aim of this book, like that of the others in the 

 series, is to illustrate biological ideas in reference to 

 a particular group or class of animals. In this case 

 the selected class is that of birds, and the book applies 

 to these fascinating creatures such biological concepts 

 as adaptation, struggle, sex, heredity, variation, selec- 

 tion, and behaviour. 



There are many students of birds who are expert 

 along particular lines, having, for instance, a personal 

 familiarity with British birds and their ways, or an 

 accurate knowledge of birds' bones or birds' eggs, or 

 a detailed acquaintance with what is known in regard 

 to distribution, migration, and the nature of the food, 

 or a quite remarkable eye for flight, and ear for song. 

 We have had the pleasure of learning much from 

 some of these experts, a pleasure all the greater be- 

 cause the lover of birds is usually a delightful person 

 to meet ; perhaps we shall not be misunderstood if 

 we say that this book is an attempt to unite all the 

 specialisms in an amalgam of biological ideas. 



For those who have the good fortune to be nearer 

 the beginning than the end of their studies, our book 

 may be, we hope, of use in suggesting the length and 

 breadth, the depth and height of the Biology of 

 Birds. 



University of Aberdeen, 

 spring, 1923. 



V a2 



