554 TEE POPULAR SCIENCE MONTHLY 



begins to take the reins, though feebly at first, into its own hands. Out 

 of many experiments made upon the young of our common wild birds 

 I select by way of illustration the brown thrush and black-billed cuckoo. 

 In July 24, a nest of this thrush which I had been watching contained 

 three birds, the youngest of which barely had its eyes open, and was 

 from twenty to thirty hours old. When taken from its nest, at 

 3 :15 p.m., and tested in the way suggested above, I obtained one 

 hundred food reactions in thirteen minutes, each representing the entire 

 complex of movements already analyzed, and each lasting from three to 

 fifteen seconds, according to the strength of the stimulus received. A 

 test immediately following gave fifteen reactions to the minute. The 

 reaction time, which was very rapid at first, seemed to slow down only 

 as a result of fatigue, but there was not a single failure to react upon 

 the given stimulus. The same reaction was produced by clapping the 

 hands, touching the bird, or holding its head between the fingers. On 

 this day the two older birds, which were from two to three days old, 

 would react while in the nest, but not when out of it. Now, upon the 

 next day, about twenty-four hours later, as well as upon subsequent 

 days, when the same tests were made with the same birds none of them 

 would react when removed from the nest, with the exception that one 

 feeble response was obtained from thrush No. 3, on July 25. 



The same result was obtained with cuckoos. I was unable to get 

 a single food-response from a black-bill, four or five days old, during the 

 twelve hours or more that it was held a captive away from its nest. 

 It would have starved rather than open its mouth of its own accord, 

 and it even regurgitated the food which was pressed into its throat 

 and gullet. Its whole conduct showed conclusively that the sense of 

 fear had not yet appeared, but the moment this hungry bird was 

 returned to its nest, and its feet touched the familiar twigs, it seemed 

 to expand, as by magic, into a new creature, for standing erect, with 

 every feather tube raised, and with vibrating wings, the neck trembling 

 like a tuning fork, it opened its mouth and gave the food-reaction with 

 all the vigor of which it was capable, and gave it repeatedly, loudly 

 calling. 



Edinger speaks of the modification of behavior described above, as 

 an acquired habit, by which nestlings assure themselves against impend- 

 ing danger, and compares their attitude with that of an old bird coming 

 hesitatingly to the nest, and looking about as if in anticipation of 

 trouble. A simple experiment, however, like that just given upon the 

 cuckoo, shows that this modification has nothing to do with assurance, 

 for it begins long before there is any decided evidence of fear, and the 

 little bird does not begin to look about in a suspicious manner until it 

 is six or seven days old, when fear is arising. Moreover, all the atti- 

 tudes, expressive of this instinct, both in young and adult, must, I 

 believe, be considered as instinctive and not acquired. 



