68 



HOMING AND RELATED ACTIVITIES OF BIRDS. 



its own nest at 6 after some hesitation. The change in the position of the stake was a dis- 

 turbing factor, but was not sufficient to determine the choice of nests. 



The line of weeds forming the northern boundary of the triangle was next moved a foot 

 to the northward. The bird returned by its customary path without the slightest hesita- 

 tion. This landmark played no part whatever in orientation. 



The weeds were returned to their original position and the objects forming the western 

 border of the triangle were moved a foot to the northward. This brought the clump of 

 weeds and palm leaf, originally at g and /, to the position shown in the figure. The bird 

 alighted far to the south and passing around between h and e took the northern nest at c 

 and settled down quietly. She was driven away and the palm leaf was returned to its 

 original position, /. The bird returned and occupied the northern nest, c, for 5 minutes. 

 She was again driven away and the clump of weeds was returned to its original position, g. 

 The bird returned and took the southern nest, 6, without hestitation. The leaf and weeds 

 were moved back to d and /. The bird chose the northern site; they were returned to the 

 southern position, the bird returned to the northern neat, adjusted the egg, got up, walked 

 to the southern nest, and covered the egg there. 



Fig. 4. — Environment of the nest described in experiment 6. 



The weeds were moved northward to /, the leaf was not disturbed. The bird chose the 

 southern nest. The leaf was moved to the northward. The bird chose the northern nest. 

 Leaf and weeds were moved to the southern position; the bird came to the northern nest, 

 hesitated for 30 seconds, then chose the southern nest. This shift was repeated many times 

 until it was quite certain that the bird always took the same position with respect to the two 

 objects. Finally they were removed entirely. The bird showed signs of confusion, occupied 

 the two nests alternately for several minutes, and finally settled down in the southern nest. 



The weeds to the northward were cleared away and the nest, 6, was moved 18 inches to 

 the northward of c, to a position at the extreme right of the figure. The leaf and weeds 

 were likewise shifted to the northward, so that the original relations of the nest and two 

 objects were now duplicated, nearly 3 feet from the original position. The bird returned 

 and covered the southern egg at c; 3 minutes later she got up, went to the new nest, adjusted 

 the egg, and covered it. I watched her for half an hour longer, during which time she 

 remained contentedly on the nest; 4 hours later her mate had returned and taken the 

 southern nest, which he occupied during the whole of the following day. 



From this rather long account it is clear that the final orientation was deter- 

 mined wholly by the visual stunulus of two objects in the neighborhood of the 

 nest. Neither the palm leaf nor the clump of weeds alone was sufficient to 

 determine the choice of the nest, but both together called forth a definite 

 reaction, regardless of all other objects in the vicinity. 



Watson found that considerable changes could be made in the vertical posi- 

 tion of the nest without affecting the bird's reaction in the slightest. His 

 experiments have been repeated, but always with negative results. The fol- 

 lowing notes illustrate the type of reaction obtained: 



