THE REACTIONS OF BIRDS TO SOUND STIMULI 209 



considerable extent. There is a possibility that auditory stimuli 

 may sometimes have been accompanied by visual stimuli in 

 the case of the thrushes when the giving of the sound required 

 motion on my part. My blind was pitched between the nest 

 and the morning sun, and the tent- walls were very thin, so that 

 movements within it were often perceived vaguely from the 

 outside. 



The reactions to all these stimuli were more or -less similar, 

 differing in degree only. In every case they consisted of move- 

 ments of the head and of the bill, of raising the wings, and of 

 winking. The eye-wink, however, is of doubtful value, and 

 was considered only in the case of the thrushes. The interval 

 between the giving of the stimulus and the perception of the 

 reaction to it seemed fairly constant for those birds which reacted 

 at all, being about three-fourths of a second, as nearly as could 



be determined. 



III. OBSERVATIONS 



1. On the nesting hermit thrush. July 10, 9:10-10:50 a. m., 

 1 :30-3 :20 p. m. The bird was not much alarmed, even at the 

 very first, by my stirring about in the tent, but flew when, at 

 9:20, I caused the side of the tent toward the nest to flutter. 

 It returned in two minutes, and took its usual position on the 

 nest, facing the tent obliquely, with its head turned toward the 

 woods, to which the bird always went on leaving the nest, rather 

 than toward the lake. Only rarely, and then usually in response 

 to sound stimuli, did it turn its head directly toward the tent. 

 I never saw it approach the nest except from the side toward 

 the blind. 



The first time that I released the shutter of my camera the 



bird showed decided* alarm, but this was of short duration, 



less than three seconds. Rapping with a pencil on the metal 



cover of my note-book caused the bird to turn its head from 



side to side, as if it were trying to locate the source of the sound. 



A short blast on the whistle caused the same reaction, apparently 



of about the same intensity; when this experiment was repeated 



the same result was obtained, but after the tenth trial the bird 



seemed to have become accustomed to it, and the only response 



it made was merely to assume a more alert attitude. 1 



1 Similar observations were made by Strong on gulls studied from a blind. 

 Strong, R. M., 1914. On the Habits and Behavior of the Herring Gull, Larus 

 argentalns Pont. The . Auk, vol. 31, Nos. 1-2, pp. 22-49, 178-199; plates 1-10, 

 19, 20, also Smithsonian Report, 1915, pp. 479-509. 



