218 ROLAND F. HUSSEY 



raised its wings when I clapped my hands. To the whistle 

 blasts the kildeers responded at first by running a few steps 

 along the shore, but later they gave no reaction to this sound. 

 To duckings they did not respond, but when I clapped my 

 hands the whole flock took flight. The visual stimulus un- 

 doubtedly was the stronger in bringing about this reaction. 



Later I made similar experiments on a solitary kildeer, without 

 obtaining any positive results. 



IV. SUMMARY 



1. The hermit thrush was constantly on the alert as long as 

 I was in the observation tent, and while I was there it seemed 

 very often to be more sensitive to sounds from without the 

 tent than to those which I made inside. 



2. If a continued sound were suddenly interrupted by another 

 loud sound of a very different character, the bird reacted more 

 vigorously in most cases than to either sound alone. 



3. The hermit thrush seemed not particularly sensitive to 

 sounds when no one was in the tent. 



4. An auditory stimulus produces a much stronger reaction 

 in birds when it is reinforced by a moving visual one, and a 

 moving visual stimulus when it is reinforced by an auditory 

 stimulus. 



5. The hermit thrushes under observation very soon became 

 accustomed to various sounds and in a short time ceased to 

 react visibly to them unless the sounds were reinforced by 

 other stimuli. 



6. The hermit thrush was very much more sensitive to sound 

 stimuli early in the period of experimentation than later, and 

 there was a secondary maximum just after the hatching of 

 the eggs. 



7. The reactions to sounds on the part of the hermit thrush 

 are very much inhibited when the bird is at the nest or within 

 three feet of it, but this inhibition is much less after the young 

 are fed than before. 



8. The adult hermit thrush is apparently more sensitive to 

 notes of higher pitch than to sounds of lower pitch. 



9. Very young birds were more influenced by such sounds as 

 the rustling of paper or of birch-bark than by sharper sounds 

 such as tappings, whistling, etc. 



