NESTS AND NEST-BUILDING IN BIRDS 371 



result of individual acquisition, due at least to the association 

 of motor impulses ^^ith sense impressions. There is further, 

 evidence that birds adapt means to ends or do things to effect 

 changes which they seem to desire to bring about. In other 

 words at times they seem to strive with an end in view, and con- 

 tinue to work until their aim is achieved. Whether such acts 

 as we now refer to are really attended by an association of ideas, 

 or merely result from the gradual elimination of useless mo^'e- 

 ments after successive trials, we cannot say. 



Habits, it is true, are likely to arise at every step, and we 

 have already seen how quickly birds acquire a certain way 

 of approaching and leaving their nest-sites. That the method 

 of dealing with the nest material is remarkably uniform has 

 been suggested from the analysis of the structure of nests already 

 given. Such facts, not to speak of the aberrations and eccen- 

 tricities already accounted for, speak loudly for the cardinal 

 role of instinct in all nest-building operations. As to adapting 

 means to ends we might refer to the behavior of robins in their 

 use and treatment of strings when difficulty arises (see p. 348). 

 Compare also the behavior of bluebirds, house martins and 

 wrens in their efforts to carry into their nest-boxes, straws 

 and twigs, which are too long for the hole. When such a bird 

 is brought up at a short turn at the entrance, it usually tries to 

 force a passage, and upon failure repeats the attempt until it 

 either succeeds or drops the object. Like the dog trying to 

 carry a stick through a hole in a fence, the object is bound to 

 be shifted back and forth in the mouth, until held in a certain 

 position, when it is able to push it through. It seems probable 

 that in the case of the bird the right shift of the bill to one end 

 might in a certain proportion of cases quickly lead to the forma- 

 tion of a useful habit. According to a writer in Bird-Lore,'^ 

 this appears to have been the case with a pair of house wrens, 

 both of which learned the trick of slipping the bill to one end 

 of the twigs, and thus pushing them into the opening. The 

 male was an adept at this and his mate though unskilled at 

 first soon acquired the habit, and " it was not long before, upon 

 bringing a twig to her door, she would deliberately begin to 

 move her bill to one end or the other. ' ' 



^* Thorns, Craig S., Must Wrens be Taught Nest-Building. Bird- Lore, vol. xii, 

 p. 181. New York, 1910. 



