Nest-Building 161 



not of the proper sort, one is at a loss to explain such a de- 

 parture from their usual custom. However, whatever may 

 have been the previous experience of these birds, this nest, 

 though completed, was never occupied, and in three days it 

 was torn down and the materials disappeared. 



The nests of Chipping Sparrows are notoriously defective in 

 point of stability, and frequently suffer from this cause, as 

 well as from a lack in the proper materials of construction. 

 Although the hair lining is well modeled, a proper foundation 

 is seldom laid, and the whole fabric is often so thin that the 

 eggs can be seen through its walls. The winds frequently 

 knock the bottoms out of such nests, but the Sparrows are 

 incapable of profiting from such experiences, and persist in fol- 

 lowing a stupid instinct which in this case is veritably a blind 

 and inefficient guide. 



While watching the Robins and Chebecs, I could also follow 

 the behavior of a pair of these Sparrows who were engaged in 

 the same operations. The same molding movements which we 

 have described were repeated in the Sparrows. After this nest 

 was essentially finished the behavior of both birds was most 

 suggestive of the instinctive character of all their actions, and 

 of their chain-like relation. The female would drop to the 

 ground, twittering all the while, and with wings spread and 

 quivering await the approach of her mate; the action was 

 usually quickly repeated, when the female at once repaired to 

 the nest, sat in it for a few minutes, and then flew off. In the 

 course of a little over two hours, these actions were repeated 

 four times. At eight o'clock in the morning of the following 

 day there was a repetition of this performance, the female 

 always going to the nest and remaining about three minutes; 

 at times there would be a recurrence of the molding movements, 

 but nothing was added to the structure. These actions were con- 

 tinued until the first egg appeared, and illustrate in the clearest 

 manner how one set of serial instinctive acts shades into another 

 series, which are also instinctive, but of a different character. 



