Wild Birds. 



thus normally completing one term of the series before passing to the next in sequence. 



The machinery, however, rarely works with absolute precision. Perturbations are sure to 



_. - arise whenever a contrary impulse 



comes into the field, and either blocks 

 the path or struggles for supremacy. 

 The surge of parental feeling is 

 often marked by an inbred pugnacity, 

 which begins to show itself in certain 

 species at the very beginning of the 

 breeding season. This fighting mood, 

 which is an adaptation for the protec- 

 tion of the home and all that it con- 

 tains, is by no means a measure of 

 the other parental impulses. It has 

 a gradual rise, reaches a maximum 

 when the young are ready to leave the 

 nest, at a time when protection is 

 most needed, and then gradually sub- 

 sides. 



When a pair are robbed during 

 the breeding season, or in any way 

 disturbed in mind or property, three 

 courses are open to them, either to 

 desert and begin operations anew, 

 to stay by the nest and save what is 

 left, or, having done this, to fill up 

 the gap by laying more eggs. The 



course eventually followed depends upon the nature of the bird, or upon the relative 



strength of fear, the parental instincts, and habit. 



The parental instinct, 1 reenforced by habit, gradually increases until the young are 



reared. It is therefore safest to change the nesting surroundings when this instinct is 



approaching its culmination. 



The general feeling of fear is gradually or quickly suppressed according to the value 



of the different factors in the equation, by the parental instinct, which impels a bird at all 



hazards to go to its young wherever placed. This impulse though it be weak at first, 



is strengthened by exercise, or what amounts to the same thing, by the growth of 



habits or associations. 



After a bird once visits the nest in its new position, it returns again and again, and 



in proportion as its visits to the old nesting place diminish and finally cease, its approaches 



to the new position become more frequent, until a new habit has been formed, or if you 



will, until the old habit is reinstated. 



When the birds approach the nest any strange objects like the stakes which support 



the bough, or the tent which is pitched beside it arouse their sense of fear or suspicion, 



1 This phrase is sometimes used for the sake of brevity and convenience in nearly the same sense as parental 

 attachment or parental love. 



Fig. 2. Tent in bushy pasture beside nest of Chestnut-sided 

 Warbler, shown in detail in Fig. 3. 



