158 Wild Birds 



repeated, a habit is sure to follow. Instincts are thus con- 

 stantly being overlaid or replaced by the results of experience. 

 This is seen in the merest trifles as well as in the more important 

 or pronounced activities. Thus, it was not long after incuba- 

 tion began before this bird had adopted a definite position, 

 while sitting on her eggs her head being always turned in the 

 same direction. Since she faced the path of approach, this 

 habit may have been determined by the habit of approach 

 already referred to, or have been dictated by convenience or the 

 ease by which the avenue of approach could be surveyed. 



Many of the details which we have recorded, such as the rate 

 of building, the amount of materials used, the time of dropping 

 the eggs, which according to some observers are laid in the 

 early morning, are relatively unimportant, for they vary with 

 the individual. Far more significant is the general stereotyped 

 character of the actions, which being so nearly the same produce 

 in all Robins so nearly the same results. Few more typical 

 examples of instinctive behavior can be witnessed in higher 

 animals than the serial acts by which the adaptive and often 

 beautiful nest of the wild bird is produced. 



The proof of instinct lies in the molding, beating, and 

 turning movements, which are not under the effective control 

 of a guiding intelligence, since they are begun before they are 

 required, are often continued longer than necessary, and with- 

 out economy of effort. As much energy is often spent over a 

 few straws as over a much larger load, even when the move- 

 ments tend to scatter rather than to consolidate the materials 

 already gathered. 



While instinct holds the reins in nest-building, the actions 

 of the builders are more or less modified or irradiated by 

 gleams of intelligence, although this does not as a rule carry 

 them very far. Here is a small instance in point : when red, white, 

 and blue yarn was thrown on the ground, the white was taken 

 almost immediately, probably because it was the more con- 

 spicuous, but it often bothered them to carry a long streamer 

 clear. Once when Cock Robin with his beak full of yarn 

 alighted on the branch and started to walk to the nest, several 



