Nesting Behavior of the Yellow Warbler. 65 



nest, and also when a gust of wind moved the nest. On 

 July 7 a simple experiment was carried on. And it was 

 found that the nestlings threw up their heads for food at 

 the snapping of fingers, scraping the pencil on the blind, a 

 low whistle, or contact with the nest. This instinct was 

 shown whenever the birds were artificially stimulated, but 

 on July 8 it became modified. For, at this time, such a 

 stimulus caused the response from one, or, possibly, two 

 birds, or from -none. As they grew they became more 

 watchful and attentive, for they perceived the parent bird 

 approaching with food at some little distance. On July 9 

 the young marked red opened its bill at the shutting of a 

 farm-house door, and both red and blue opened their bills 

 when the nest was moved by the wind. Then on July 10 

 red opened its bill at an artificial chirp. It seemed that this 

 instinct lessened each day, from July 8 on, but still it was 

 present to a certain degree when the nestlings left the nest. 



During the first half of the nestling period, the parent 

 birds evinced a peculiar habit of pecking the young, especially 

 about the eyes. It would, perhaps, be hazardous to attempt 

 an interpretation of this beyond suggesting that it might 

 simply indicate an impatience on the part of the old birds 

 for the eyes to open. The eyes of all three nestlings were 

 open by the evening of July 5, or, approximately, within a 

 period of three days and a half after hatching. After this 

 pecking about the eyes ceased, though continued on the other 

 parts of the body. 



On several occasions one of the nestlings swallowed the 

 end of a hair, which was used in constructing the nest. This 

 caused the bird much distress, and also made it impossible 

 for its food to be swallowed. When the female visited the 

 nest, on such occasions, she picked up the hair and attempted 

 to pull it out, sometimes flying in a semi-circle around the 

 nest. This certainly could become a grave danger to the 

 nestling bird, because in many cases the hair was quite se- 

 curely fastened in the gullet, and might easily result in the 

 dislodgement of the young from the nest. 



