268 RELATION OF TERRITORY TO MIGRATION 



ground already occupied, and, until reproduction 

 is completed, asserts its individuality and exer- 

 cises dominion over its territory. What, then, 

 is the prospective value, biologically considered, 

 of the changing interest that A displays in B, 

 and to what will such changes lead ? These are 

 the questions to which we will now direct 

 inquiry. 



The annual life-history of a bird is in broad 

 outline conditioned by two powerful and at first 

 sight opposing impulses — the one to live in 

 society, the other to live solitary. But, mani- 

 festly, a bird cannot be governed by opposing 

 impulses. It has but one character, within 

 which, according to the season and the circum- 

 stances, different impulses predominate. But 

 these impulses, no matter how different they 

 may appear to be, have their respective parts to 

 play in furthering the life of the individual. 

 Hence they cannot oppose, though they may 

 conflict, if the resultant behaviour contributes 

 towards survival. 



The majority of birds live to-day in constant 

 danger from predatory species, and that this 

 danger was still greater in bygone ages there 

 can be but little doubt. A curious mode of 

 behaviour of the Curlew, Whimbrel, and Godwit 

 demonstrates this, for it must be the outcome 

 of the necessity for constant watchfulness. 

 Whilst resting with its head turned back and 

 its beak buried in the feathers of the mantle, 

 the bird constantly moves the axis of its body, 

 so that an observer, if placed in a direct line 



