72 HOMING AND RELATED ACTIVITIES OF BIRDS. 



own nest, but was again interrupted by the canvas. After a great number of failures she 

 finally reached the foot of the bank, seemingly by chance, half an hour after the canvas was 

 placed in position, and from this place she followed her customary path to the nest. An 

 hour later she was driven from the nest (she probably made many trips to and from it 

 during this interval). She returned to her original alighting place at the top of the bank 

 and flew from it across the canvas to the foot of the bank, then walked to the nest. 



In this case the alighting place was far from the nest. Blocking the path 

 between the alighting place and the nest was sufficient to destroy orientation. 

 The immediate neighborhood of the nest was reached by chance, but was 

 recognized at once. Readjustment to the changes in the path followed very 

 quickly. 



From many observations I am convinced that practically every sooty has a 

 special alighting place and path which is invariably followed in the return to 

 the nest under normal conditions. In some cases the path seems unac- 

 countably complicated. Figure 7 shows the path 

 followed by one bird in 10 successive trips to the 

 nest. It passed its own nest, then around a large 

 clump of weeds, back past its own nest at b to 

 inspect the nest at c, and only then occupied its 

 own nest. 



In many cases it is evident that after orientation 

 is gained the path to the nest is determined largely 

 by motor habits irrespective of the immediate visual 

 stimuli. Little direct evidence upon the recognition 

 of the alighting place has been gained, and the at- 

 tempt to trace back orientation beyond this point 

 must be postponed until data from experiments with 

 noddies has been presented. (a) to the nest (&). 



EXPERIMENTS WITH NODDIES. 

 THE NEST AND PERCH. 



As in the case of the sooties, Watson found that the noddies locate their 

 nests readily when the appearance of the surroundings has been completely 

 altered and that the substitution of an artificial nest and egg for the originals 

 does not disturb the birds in the least. He found also that very slight changes 

 in the position of the nest confuse the noddies and that after such changes the 

 birds still react positively to the old nest site. The nests of the noddies are 

 always built upon the bay cedars and any great change in the appearance of 

 the nest and environment involves not only a great deal of labor but also the 

 destruction of many other nests. For this reason no great number of experi- 

 ments upon the nest recognition of the noddies were carried out. Such exper- 

 iments as the following, together with a large number of observations upon the 

 flight of the birds to their nests, give, however, a fairly complete picture of the 

 mechanism of orientation. 



EXPERIMENT 10. 



A pair of noddies had built their nest in a dead cedar bush near the smaller of the palm 

 trees shown in plate 7, figure 2. When both birds were at the nest, one or the other 

 was always to be seen perched on the middle of a low leaf of the palm. One of the 

 birds is shown in figure 2, c. The nest was torn from its position and fastened on top 



