254 Papers from the Marine Biological Laboratory at Tortugas. 



birds/ Under natural conditions in the field they are never in total dark- 

 ness. Starlight on the island is exceedingly bright. We can not conclude 

 from this test, however, without additional control tests (which I had no 

 time to make), that the terns run the maze wholly by means of visual data 

 or that they even learn it wholly in terms of visual data. 



EXPERIMENTS UPON THE ROTATED MAZE. 



One test was made upon the maze after it had been rotated 90 degrees 

 to the north. The birds, for example, instead of traversing S-0 in a south- 

 erly direction, must now traverse this alley in an easterly one. The rela- 

 tions of the turns, however, were not altered by this change ; only the cardinal 

 directions were altered. On account of my having to leave the island, much 

 to my sorrow, on the following day, this experiment could not be extended 

 to the other directions. The results of this test were as follows: 



SOOTY IV. 



First trial: Bird acted very peculiarly at H. Came out of H, but ran 

 tion L. Became confused, went up I, then into F and on around the long 

 way. Time: 0.91 minute. (Normal time for control test: 25 minutes.) 



Second trial: Bird badly confused. Ran full length of L, then up I, 

 then full length of Z, back down I, turned into R, then went long way via 

 E, F, and G. Time : 2.43 minutes. 



SOOTY III. 



First trial: Perfect. Time : 0.20 minute. 



Second trial: Stumbles about at H, making circus motions, apparently 

 trying to find entrance. Becomes discouraged, goes into L and runs full 

 length. Comes out and runs up I. Into F, then to O by long route. 

 \Mien he reaches the east comer of the maze, he stops and tries to poke 

 head out through the meshes of the wire. This direction had formerly led 

 to the food. Time : 2.75 minutes. 



A third trial was given the following morning. Bird ran round to S, 

 became confused, turned into E and came to O by long route. Time : 0.81 

 minute. 



SOOTY II. 



First trial: No error. Time: 0.31 minute. 



Second trial: Bird badly confused. Ran full length of L. Came out, 

 turned into S. Movements hesitating and slow. Time : 0.75 minute. 



SOOTY I. 



First trial: Perfect. Time : 0.20 minute. 



Second trial: Bird badly confused. Every error in the maze was made 

 again and again. Finally reached O by the long way. Time : 2.91 minutes. 



'Both species were tested to see if they would feed (without aid from me) in a 

 photographic dark-room. The test was very carefully made. Neither the noddies 

 nor the sooties would stir from their tracks. .\11 sounds were hushed. The sooties 

 would no longer reply to my " peep " as they would customarily in starlight. 



