NESTS AND NEST-BUILDING IN BIRDS 251 



Who would say that such untoward surroundings were deHber- 

 ately sought for the protection afforded by man? In this 

 instance a most unfavorable site was without doubt chosen on 

 account of the support and apparent protection suggested by 

 the dimly lighted hole in the frame, while quiet reigned and 

 w^hen man was absent from the scene, and then held to by 

 instinct and association, in spite of drawbacks however formid- 

 able. Attachment to the chosen site is instinctive and increases 

 hourly, while it is also strengthened through association, which 

 may come in time to rob every kind of noise and disturbance of 

 its terrors. While the ascending curve of attachment, height- 

 ened by the guarding instinct, rises rapidly, the curve of fear 

 is correspondingly depressed. The question is first a specific, 

 and then an individual problem. The upward curve ascends 

 more rapidly, it may be, in bluebird than in cedar waxwing, but 

 again this ascent may be steeper in one bluebird than in another, 

 more abrupt in a town robin than in one born and bred in the 

 woods. The last court of appeal in such a case will always be the 

 experience of the individual, and the mutual reactions of the pair. 



On the contrary I would not affirm that the robin's nest 

 which I have seen built on the stringers of a railroad bridge, but 

 a short distance below the level of the rails was built during a 

 long interval of quiet. The interval required may in certain 

 cases indeed be very short, and its necessary length will depend 

 again upon the history and instincts of the mated pair. Of all 

 such experiments which are tried by birds we may be sure that 

 many fail. 



Individual change in nest site. While many individual eagles, 

 hawks, robins or sparrows which habitually nest aloft or at a 

 certain height from the ground, occasionally come to the earth, 

 while others like the herring gulls and mallard ducks which as 

 commonly build upon the ground will sporadically ascend and 

 place their nests in trees and often at a considerable height. 

 To attribute such actions to the lessons of experience, as has 

 often been done, is quite as justifiable in one case as in the other. 

 Such conclusions seem to be rather gratuitous, and lacking in 

 the proper kind of supporting evidence. We do not rule experi- 

 ence out of the problem of behavior at this point, but are con- 

 vinced that most of such minor individual changes are due to 

 other causes. 



