78 HOMING AND RELATED ACTIVITIES OF BIRDS. 



The tendency of these chicks to run away from the strange nests no doubt 

 determined the parents' final action toward them. In the first experiment 

 recorded here, the difference in the appearance of the chicks, differing in age 

 by 5 days, was sufficient to cause some disturbance in the behavior of the 

 parents, but was not great enough alone to cause the rejection of the chick. 



On the seventh or eighth day after the eggs hatch, the birds begin to distin- 

 guish their own chicks from younger or older ones by their appearance alone. 



EXPERIMENT 17. 



(a) A 2-day chick was placed in a nest instead of the 7-day one which belonged there. 

 The adults pulled it out of the nest and forced it to crawl away. It was immediately 

 adopted by a bird whose nest had been robbed of a young chick upon the previous day. 



(6) A 1-day chick was placed in a nest instead of an 8-day chick. The parent of the 

 8-day chick returned and refused to cover the nest for 10 minutes. She continually pecked 

 at the chick, although not savagely. When she showed a tendency to leave the nest, I 

 replaced the young bird with one 3 days old. The parent returned, pecked the chick, and 

 when it started to run away, attacked it furiously. Her own chick was replaced and accepted 

 at once. After a time I substituted a 10-day chick for this one. It was attacked and 

 driven away at once. 



The parent sooty here seemed to distinguish its own young, 8 days old, from 

 1-, 3-, and 10-day chicks which were substituted for it. But the recognition 

 at this time is by no means certain, as is shown in the following observations : 



EXPERIMENT 18. 



A 6-day old chick and a young egg were interchanged. The parent of the egg drove the 

 chick away immediately. The nest from which the chick was taken was under a clump of 

 bushes. The owner of the nest examined the egg, came out from under the bushes, went 

 back and covered the egg, then came out again. She began to show an interest in the cries 

 of her chick, which was being abused by the egg parent about 3 feet away. She went over 

 and defended the chick, and finally covered it, about 4 feet from her own nest. 



I next substituted a 5-day sooty for the egg and replaced the 6-day chick in the egg nest. 

 Its parent returned and found the egg parent attacking it. She rushed to its defense and 

 covered it near the egg nest. Soon she caught sight of the young bird in her own nest. 

 She went over to it and, after looking at it carefully, drove it out of the nest. I replaced it. 

 She returned and accepted it. 



Her own chick was put back in the egg nest. She returned, defended it and covered it, 

 about 2 feet from her nest, paying no attention to the strange chick in her own nest. The 

 chicks were then interchanged, the 5-day one being placed in the egg nest and the 6-day one 

 in its own nest under the bushes. The old bird returned and defended the 5-day chick 

 stoutly against the attacks of the egg parent. She followed it for several feet as it ran 

 away and finally covered it. Her own chick caught sight of her and began to squall. She 

 was very much disturbed, got up and started toward it, turned back, and after much hesi- 

 tation finally went to her own chick in answer to its vigorous cries. As the 5-day chick was 

 always silent this may have furnished the basis for discrimination. 



I placed a chick a very little larger than the 5-day chick in the nest under the bushes 

 and the 5-day chick in the egg nest again. The parent started to defend her own chick hi 

 a half-hearted manner, caught sight of the chick in her nest, went to it and covered it. A 

 moment later she drove it out of the nest and stood for 5 minutes in the empty nest. I put 

 both chicks in her nest. She pecked the larger, but as it did not run away she covered both. 



Half an hour later both chicks were still in the nest. I placed the strange one in the egg 

 nest, where it was promptly attacked. Its foster-mother paid no attention to it, but went 

 to her own chick and nest. I interchanged the chicks. She rushed to defend her chick, 

 covered it, and paid no further attention to her own nest. 



The reactions of this adult bird are rather conflicting and hard to interpret, 

 as is true, indeed, of much of the behavior of the birds in tests upon recognition 

 of the young. Seemingly, there is here the beginning of recognition of the 



