64 HOMING AND RELATED ACTIVITIES OF BIRDS. 



rate localization of the original position of the nest, even when all traces of it 

 have been completely obliterated. The following notes give a description 

 of a typical instance of adjustment to a lateral displacement of the egg. 



EXPERIMENT 1. 



10 h 50 m a. m. I drove a sooty from her nest, obliterated the nest, and made a new one 

 with a noddy egg in the same place. In 1 minute the bird returned and in 2 minutes covered 

 the egg, after driving away two trespassers. 



10 h 53 m . I obliterated the old nest and made a new one, 1 foot south of the first position. 

 The bird alighted at the old nest and turned around as if to adjust the egg. She then caught 

 sight of the egg in its new position and went over to the new nest, then returned to the old 

 one. She then made 4 more trips back and forth between the new nest and the original nest 

 site, and finally settled down at the latter, hollowing out the sand to form a shallow nest. 

 After a minute she went to the egg, adjusted it, and settled down on it. Another sooty 

 attacked her and she drew back from the egg without defending it, looking back to the old 

 nest site. She next went to the old nest, then back to the egg, which she covered for 30 

 seconds. After one more trip to the old nest she seemed reconciled to the egg in the new 

 position. The total time required for this readjustment was 10 minutes. 



ll h 5 m . I drove her away again. She returned in 1 minute, alighted between the first 

 nest position and the new one, went first to the egg, then to the old nest site, then back to 

 brood the egg. Two minutes later she paid a brief visit to the old nest. 



ll h 10 m . Driven away again, the bird alighted near the old nest site and ran directly to 

 the egg. After 30 seconds she visited the old nest site, and again after 2 minutes. She was 

 driven away 6 times during the next half hour and at the end of this time showed an almost 

 perfect adjustment to the changed conditions, returning to the egg in 15 seconds. The egg 

 was then returned to its original position. The bird accepted it at once and paid not the 

 slightest attention to the new nest which she had just been occupying. 



In this case the substitution of noddy egg and artificial nest for the original 

 egg and nest did not affect the bird's reaction in the least. 



EXPERIMENT 2. 



In another case the egg was taken from a nest, a piece of black cloth 3 feet square was 

 spread over the nest, and the egg was replaced on top of the cloth. The bird alighted in a 

 few seconds and walked immediately to the edge of the cloth. It showed a good bit of 

 hesitation in stepping on the cloth, and walked around it, looking at the egg for many 

 seconds. In less than a minute, however, it ventured upon the cloth, seemed to lose all fear 

 immediately, ran to the egg and covered it contentedly. The total time required for 

 adjustment to the new situation was less than a minute. 



Other instances of similar indifference to the appearance of the nest and egg 

 are recorded in later experiments and make it clear that, except under unusual 

 conditions, the individual characters of the nest and egg do not play any 

 important part in orientation. The birds react positively to any nest at the 

 chosen site. In contrast to this the birds are almost always very greatly dis- 

 turbed by a lateral displacement of the nest of only a few inches and react to 

 the original nest site much as did the bird described in experiment 1. The 

 time required for readjustment to such slight changes varies greatly with 

 different birds, even under quite similar conditions. 



EXPERIMENT 3. 



The same birds whose average time of adjustment to disturbance is given on page 63 were 

 used for a comparison of the times of adjustment to a change in the position of the nest. 

 The nests were similarly located in open, rather thickly populated areas, but so far apart 

 that no two of the birds under observation were disturbed at the same time. In each case 

 the nest was obliterated, a new nest was constructed 1 foot from the old nest site in the 



