196 'Journal of Coiupardiive Neurology and Psychology. 



in the previous paper, the wild bird commonly passes through a cycle of instincts 

 which mark the breeding season. This cycle is made up of eight or more terms, 

 which follow in serial order, and some of which are recurrent. Normally the bird 

 passes from center of influence I to center 2, 3, and so on, to the end of the cycle. 

 There is little overlap or blending, the bird remaining under the influence of a 

 given instinct or series of instincts, such as nest building, incubation, or feeding the 

 young until its instinct in any given direction has been satisfied, before entering a 

 new sphere or being swayed by new impulses. When the correlation or attune- 

 ment is perfect the instincts of mother and child fit like lock and key. Like clocks 

 beating synchronously the instincts of mother and child are generally in harmony, 

 but one of the clocks occasionally gains or loses, stops or runs down; one term is 

 liable to be weak or to drop out altogether, so that there is an overlap or a gap in the 

 series which may be serious. On the other hand, one term may be unduly strength- 

 ened, like nest building or incubation, and a preceding or following term corre- 

 spondingly weak. In all such cases there are eccentricities of conduct, which, if not 

 fatal to the young, are very puzzling to the naturalist. 



Most wild birds normally pass one reproductive cycle in the season; a certain 

 number, however, begin, but do no complete a second cycle; further, many like the 

 robin and bluebird not only begin but complete a second and even a third cycle 

 within the breeding period. 



The repair of the old nest in autumn by fish hawks or eagles is not done "in anti- 

 cipation of spring," and implies no more intelligence than the building of the original 

 nest. It is simply the recrudescence of the building instinct, due to the beginning 

 of a new reproductive cycle which is never finished. 



Leaving the young to perish in the nest in autumn is brought about by the scamp- 

 ing of the cycle at the other end. The migratory impulse overlaps and replaces the 

 parental instinct. 



An adult robin has been seen to offer a string to its fully grown young, and try to 

 cram it down the throat of the fledgling. Later, the old bird flew with the string 

 into a tree. This was the result of the overlapping of two reproductive cycles, or of 

 the last term of one cycle, and the first term of a succeeding cycle. The bird was 

 alternately swayed by opposing impulses, now being impelled to gather nesting 

 material, when she picked up the string, now by parental instinct to feed her young, 

 when she tried to serve it, and again possibly by the instinct of building when she 

 flew with the string into a tree. 



Building more than one nest can be accounted for by excessive development of 

 the building instinct, or by the influence of fear repeatedly interrupting the cycle, 

 together with attachment to nesting site, but the discussion is too long for this 

 abstract. 



The rebuilding of nest on nest, giving rise to the wonderful storied structures 

 sometimes produced by the summer yellow bird, or vireo, when plagued by the 

 cowbird, so that the foreign egg is buried out of sight, is not an illustration of reason, 

 as commonly suggested, but the curious result of a pure instinct. The reproductive 

 cycle is broken by fear, and a new one is begun, and in these rare cases the old nest 

 is retained as a site to be build upon. Instead of having two supernumerary nests, 

 both of which may contain eggs, as in reported cases of the phoebe, we have a series 

 of superimposed nests. The new nest is not built to conceal the cowbird's egg, 

 although it does so perfectly, any more than the addition of new materials to the 



