NESTING ACTIVITIES OF NODDY AND SOOTY TERNS. 73 



of a stake, a, 3 feet farther from the perch, c, than its original position. At this time 

 only one bird was present at the nest. It was frightened away and did not reappear 

 for some minutes after the change was effected. It was first identified again as it hovered 

 over the old nest site. Thence it flew to the perch, c, then back to the first position of the 

 nest. This was repeated several times. 



Without paying the least attention to the nest at a, the bird next flew to the large palm, b, 

 circled close around its stem, and darted back to the perch. Without alighting here it 

 turned and dropped quickly to the bushes where the nest had been. This was repeated 

 many times until it seemed quite certain that the sight of the large palm furnished the clue 

 to the position of the perch and that the change in direction of flight from the perch to the 

 nest was effected largely in terms of kinaesthesia. 



Three points were brought out by these observations. First, the existence 

 of a well-localized perch corresponding to the alighting place of the sooty; 

 second, the use of other very conspicuous objects (in this case, the large 

 palm) as points from which orientation is gained; third, the importance of 

 kinaesthetic-motor habits even in determining the direction of flight. The 

 perch seemed to be recognized partly by its appearance and partly by its 

 relation to the neighboring palm tree. 



EXPERIMENT 11. 



The nest of a noddy, upon a low clump of bushes, 30 feet from any other noddy nest, was 

 torn from its position and placed 2 feet away at the same level upon the same group of 

 bushes. The nesting bird returned, circled about the nest, and alighted upon it immediately. 

 She covered the egg at once, but seemed a little uneasy. As the nest was not very secure 

 in its new position, its unsteadiness may account for the bird's restlessness. 



The nest was next fastened on top of a stake 3 feet above its original position. The bird 

 came back from the westward toward the old position of the nest, caught sight of the new 

 arrangement, and swerved out of her straight course. She circled the nest three or four 

 times, always keeping below the new level at the same height at which she usually flew above 

 the bushes. She then flew out to sea, turned, and came back to the shore. The roof of a 

 small porch on one of the old buildings offered a convenient perch about 20 feet east of her 

 nest and she flew up to this. The most interesting part of her whole reaction occurred here. 

 Instead of alighting on the roof, she hovered beside one corner of it for a moment, then 

 turned and darted unhestitatingly to the old nest site, 3 feet below the nest. She repeated 

 this time and time again, flying to the corner of the porch roof, back a foot above the edge 

 of the bushes past the nest, up into the air, and back to the porch roof. She showed no 

 disposition to alight upon the nest after 15 minutes. 



The nest was next lowered to a foot above its original level and 2 feet to the northward 

 of its first position, just at the edge of the clump of bushes. The bird now began to hover 

 above it, but still flew repeatedly to the porch roof and back to the original position of her 

 nest. In 15 minutes she gained courage to alight upon the nest and cover the egg. Half 

 an hour later she was driven off. She returned at once, following the edge of the bushes, 

 and alighting upon the nest. 



The nest was next moved 6 feet farther north. The bird returned along the edge of the 

 bushes, hovered for a moment at the old nest site, then flew up and alighted upon the porch 

 roof. From here she flew directly upon the nest, 5 minutes later she returned to the old nest 

 site, from there flew out to sea, then back to the porch roof and to the nest. 



On the following day the nest was moved 6 feet farther north. In the meantime the mate 

 of the sitter had returned and both birds had become accustomed to the new position. 

 When it was moved this time, instead of flying out to sea they both hovered about, striking 

 at me, and they alighted upon the nest while I was still adjusting it. I moved it about for 

 short distances in several directions, changed its level several times, and always the birds 

 took it immediately. The visual stimulus of the nest seemed to have become the principal 

 factor in orientation. To test this the stake supporting the nest was replaced by a tripod, 

 the nest itself was covered by a black cloth, and the egg placed on top of this. (Such changes 

 had been found to have no effect when made with nests otherwise undisturbed.) The sitter, 

 the same one upon which former experiments were made, came back past the old nest site 



