NESTING ACTIVITIES OF NODDY AND SOOTY TERNS. 75 



may be kept in sight constantly during the flight and time and time again are 

 seen to follow the same path from and to the nest. The great majority of 

 birds in such short flights return by rather definite pathways indicated by the 

 dotted lines in figure 2. As will be seen from the distribution of the nests, 

 these lines lead directly to the chief nesting areas, and the preponderance of 

 birds following them may be due simply to this fact. In each case, however, 

 the path is near a conspicuous landmark (the buildings and opening in the 

 bushes) , and the birds frequently change their direction of flight after passing 

 these, as is indicated by line d, figure 2, which is the route followed by one bird 

 in a number of trips to the nest. It seems almost certain that these prominent 

 visual objects are the directing factors in the orientation of the birds when 

 approaching the island. 



SUMMARY OF WORK ON NEST RECOGNITION. 



The general method by which the birds reach their nests may be summarized 

 as follows : Coming in from the sea, they direct their flight by the more con- 

 spicuous features of the island, the buildings, prominent bushes, etc. From 

 these the direction is taken along the shore-line, or the edge of the cleared 

 nesting area to the alighting place, which also offers prominent visual stimuli. 

 From this the path to the nest is followed, either by a series of visual-motor 

 habits built up around other nests, debris, etc., or by a series of kinsesthetic- 

 motor habits irrespective of external stimuli. Study of orientation at night is 

 practically impo.ssible, both because of the difficulty of identifying the birds 

 and, chiefly, because of their increased timidity. During the breechng season, 

 however, the nights are never so dark as to render the chief landmarks invis- 

 ible at close range and, with direction gained from these, the birds' kintes- 

 thetic-motor habits are adequate for further orientation. 



The study of orientation in the nest locality has given no positive evidence 

 upon the method of orientation at greater distances from the nest, but it does 

 furnish two negative pomts of some importance. First, in the nest locality 

 the birds are dependent upon visual and kinesthetic habits for orientation and 

 show no evidence whatever of the possession of any special sense of locality, 

 such as a magnetic sen.se, functional within short flights. Second, kintes- 

 thetic-motor habits are formed with no such rapidity as to suggest that the 

 birds can retrace a path by memory of its successive directions and distances 

 when these have been experienced only once. As in all animals, vision tends 

 to be replaced by kinaesthesia as habits become fl.xed, but the process is rela- 

 tively slow and plays no great part in orientation. 



