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SCIENCE 



[N. S. Vol. XXV. No. 646 



been satisfied, before entering a new sphere 

 or being swayed by new impulses. When 

 the correlation or attunement is perfect the 

 instincts of mother and child fit like lock 

 and key. To change the figure, like 

 clocks beating synchronously the instincts 

 of parent and child are generally in 

 harmony, but one of the clocks occa- 

 sionally 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 strengthened, like nest 

 building or incubation, and a preceding or 

 following term correspondingly 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 repro- 

 ductive cycle in the season ; a certain num- 

 ber, however, begin, but do not complete 

 a second cycle; further, many like the 

 robin and bluebird not only begin but com- 

 plete 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 recrudes- 

 cence of the building instinct, due to the 

 beginning of a new reproductive cycle 

 which is never fiinished. 



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 over- 

 lapping 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 ma- 

 terial, when she picked up the string, now 

 by parental instinct to feed her young, 

 when she tried to serve it, and again pos- 

 sibly by the instinct of building when she 

 flew with the string into a tree. 



Building more than one nest can be ac- 

 counted for by excessive development of 

 the building instinct, or by the influence of 

 fear repeatedly interrupting the cycle, to- 

 gether 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 cow- 

 bird, so that the foreign egg is buried out 

 of sight, is not an illustration of reason, 

 as commonly believed, but the curious 

 result of a pure instinct. The reproduc- 

 tive 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 iuilt 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 this perfectly, any 

 more than the addition of new materials to 

 the osprey's nest in the fall is in the nature 

 of repairs, although it answers this pur- 

 pose admirably. The nest is built because 

 the bird is at the opening of a new cycle, 

 and is impelled by the building instinct. 



Many confirmatory facts could be given. 

 The herring gull will not only bury an 

 egg, in rebuilding on its old site, in this 

 case the discarded nest, when its cycle has 

 been interrupted by fear, but will bury 

 its dead young which it treats as so much 

 nesting material. 



