210 ROLAND F. HUSSEY 



entirely quiet, I repeated the experiments with various kinds 

 of sounds, as whistling, rapping on wood and on metal, clapping 

 my hands, etc., but I was unable to detect any positive reactions. 



I also continued the observations on the inhibition of reac- 

 tions in the parent when near the nest, with the same results 

 as before. 



July 25, 8:25-10:30 a. m. The observations made from the 

 tent this morning were substantially the same as those of the 

 day before, except that for the first time I was sure that both 

 parents came under my observation. I was not able to detect 

 any difference in their behavior. 



At 9 :45 I left the blind and withdrew for about ten minutes. 

 On my return I waited until a parent had finished feeding the 

 nestlings and had left the nest, and then, instead of going to 

 the blind at once, I took advantage of some natural cover to 

 conceal myself. Neither of the parent thrushes seemed to pay 

 the slightest attention to me on their subsequent visits to the 

 nest, nor did either of them respond visibly to any sound that 

 I made, though I tried shouting, whistling, and chirping loudly. 

 But after I reentered the tent (at 10:15) I found that both birds 

 reacted markedly to these same sound stimuli. 



2. Observations on a young hermit thrush. In the late after- 

 noon of July 26 a young thrush was taken from this nest for 

 the purpose of studying its reactions to sounds under laboratory 

 conditions. On this date it gave no evidence of reactions to 

 sounds or of the formation of associations between sounds and 

 other events. On the two days following there was no oppor- 

 tunity to study this bird. 



On July 28, a very warm and sultry day, the bird became 

 sick, due doubtless to the heat and to the change in environment 

 and feeding; it was transferred to a more airy cage. The next 

 day the temperature was still higher and the bird was still sick ; 

 yet it was very active, and made violent efforts to escape from 

 the cage, with the result that it so nearly exhausted itself that 

 it was practically unable to open its eyes. It was on this date 

 that the first observations were made which showed any ability 

 on the part of the' bird to associate sounds with other events. 

 For instance, after the bird had been fed four times, it was 

 noticed that when the door of the cage was rattled the bird 



