74 HOMING AND RELATED ACTIVITIES OF BIRDS. 



directly towards the nest, swerved when 3 feet from it, and returned to the old nest site. 

 This was repeated four times. She then alighted upon the nest, but flew away immediately. 

 Her mate came up and both circled around the nest for some time, but did not alight. The 

 cloth was removed and the first bird covered the nest within five seconds. 



The nest was then moved 30 feet to the southward of its original position. The bird came 

 back to the northern site, circled around for a moment, then alighted at the original position 

 of the nest. She looked about, caught sight of the nest in its new position, flew directly to 

 it, and covered the egg. A few minutes later she became dissatisfied and began to fly about, 

 circling from the porch roof to the old nest site, to the nest, and back to the porch roof. 

 She did not settle down before dark. On the following day both birds were observed at the 

 nest, adding sticks to it and apparently quite satisfied. The next day both were gone and 

 were not seen again. 



These observations, like the preceding, lay emphasis upon the perch as a 

 conspicuous visual stimulus from which the birds gain accurate orientation to 

 the nest. When this method of reaching the nest failed, the birds came to 

 depend upon the visual stimulus of the nest and were confused by the changes 

 in the appearance of the nest. 



The method by which the noddies recognize their nests is very similar to 

 that of the sooties, the only difference being the manner of approaching the 

 nest in the one case by flying, in the other by walking. The perch has for 

 the noddies much the same relation to the nest as the alighting place has for 

 the sooties. Recognition of the noddy perch seems to be partly in visual 

 terms, partly in the relation of the perch to other very conspicuous visual 

 objects, such as the palm in experiment 10. 



Destruction of both the alighting place and nest gave no very definite 

 results. In one instance the birds flew back and forth along the edge of a 

 row of bushes in which the nest and perch had been located, and made swift 

 flights out around a number of tall stakes which had been planted to mark 

 other nests. In almost every instance the destruction of the perch and re- 

 moval of the nest brought out some antecedent factor in orientation, such as 

 the stakes mentioned above, but these factors were so widely distributed and 

 varied as to be practically beyond experimental control. 



ORIENTATION IN APPROACHING THE ISLAND. 



In the two experiments recorded it seems clear that the birds gained their 

 first orientation from the visual stimulus afforded by the palm trees and build- 

 ings, and from a large number of observations I feel certain that all the birds, 

 on approaching the island, determine their direction with respect to the more 

 prominent visual features of buildings, trees, and bushes. The paths followed 

 by the birds coming in from sea seem to give the best evidence of this. 



Figure 2 shows the more prominent features of the island, the buildings and 

 trees at the western extremity, a wide opening in the bushes above the southern 

 beach, and the denser growth of bushes in the central and northern parts of the 

 island. The prevailing winds during the nesting season were from the north- 

 east. When the birds are frightened they run from their nests, leap into the air, 

 and fly against the wind until they reach a height of from 10 to 25 feet, then 

 turn quickly and fly with the wind until well away from the island. If not 

 badly frightened, they turn when 20 to 200 yards in the lee of the island and 

 fly back rapidly against the wind to the region of the nest. Birds in open areas 



