Method of Bird Study and Photography 7 



the typical migratory movements, the principal terms of the 

 reproductive cycle may be expressed more fully as follows: 



(1) Spring migration of the summer residents to the place 

 of birth ; 



(2) Courtship and mating, often with the accompaniment 

 of song ; 



(3) Selection of nesting site and construction of the nest; 



(4) Egg-laying; 



(5) Incubation; 



(6) Care of the young in the nest, including feeding, brood- 

 ing, shielding or "spreading," and cleaning nest and young; 



(7) Care and "education" of young from time of flight; 



(8) Fall migration to winter quarters. 



The number of species of birds already described exceeds 

 twelve thousand; they are distributed over the entire globe, and 

 while all conform closely to a single anatomical type their vari- 

 ability, which is expressed in instincts, as well as in color and 

 form, is almost without limit. 



The emotional life, and consequently the parental instinct is 

 greater in birds than in any other class of animals excepting the 

 mammals. Their body temperature (100-112 F.) exceeds that 

 of all other animals, and is an index of their great vitality and 

 consequent activity. In the breeding season their emotional 

 behavior reaches its climax. This implies profound seasonal 

 changes in the body, especially in the nervous system, although 

 the precise nature of these changes is not known, and more 

 obviously in the reproductive cells, the vocal organs, and the 

 plumage. All birds are in full dress at this season, and they all 

 molt immediately after it. In many cases a prenuptial molt 

 further occurs. The succession of molts varies in different 

 species, but it is always of a very definite character. While 

 singing may be exceptionally heard at other times, it is richest 

 in the breeding season; it is always best in the male, and often 

 developed only in that sex. 



Birds seem to follow one line of conduct, whether it be build- 

 ing nests, sitting over eggs, or brooding and tending the young, 

 until their instinct in any given direction has been satisfied, thus 



