THE REACTIONS OF BIRDS TO SOUND STIMULI 213 



side, and looked for it when once its approximate location had 

 been determined from the sound. After about half a minute, 

 however, the bird gave up the search and paid no more attention 

 to the watch. 



The bird now seemed constantly on the alert for sounds from 

 the tent, having seen me enter it; very slight reactions were 

 noticed, however, to whistling, shouting, and clapping the hands, 

 while rapping on wood and chirping with the lips produced no 

 visible reactions. 



July 16. The three eggs hatched this afternoon. I made no 

 observations. 



July 17, 8:40-9:30 a. m., 1:10-3:10 p. m. There was no sign 

 of either parent during the fifty minutes I spent in the tent 

 in the morning. In the afternoon one of the parents was at 

 the nest when I approached, and stayed while I entered the 

 tent. On this date, for the first time, I obtained a response 

 to the chirping sound. To it the bird responded by turning 

 the head, often as much as 90 degrees, and by winking. Although 

 the interval between winks varied between such wide limits as 

 two seconds and thirteen seconds, I think that the wink can 

 safely be considered as a part of the reaction, since in each 

 case it accompanied the turning of the head, about three-fourths 

 of a second after the sound stimulus was given. 



To the higher-pitched of the two whistle notes the bird again 

 reacted slightly more vigorously than to the lower; the reaction 

 here consisted in turning the head and closing the bill. The 

 reaction to this sound was on this date much less vigorous than 

 that to the chirping. 



I tried a new vocal sound successfully; a rapid, rolling 

 " rr-r-r-rr." To this the bird responded on six out of seven 

 trials, showing alarm not merely at the beginning of the sound, 

 but as long as it was continued. 



The experiment of changing from one sound to another of a 

 different sort gave results this day on only three trials out of 

 seven. However, the bird seemed more responsive to all other 

 tests than on the last day that observations were made before 

 the hatching of the eggs. 



July 19, 9-10:40 a. m. The young birds' eyes were just 

 opening when I began my observations. Any small sound from 

 the tent seemed to stimulate the nestlings to raise their heads 



