23-2 Papers from the Marine Biologieal Laboratory at Tortugas. 



with great effort squeezed through the hole in 0.25 minute. I then re- 

 moved all the sand and left the box in position as before. On the follow- 

 ing day, since the unmarked bird (female) was on the nest, no further tests 

 were made upon the male. On the second day from the above I contintied 

 my tests. 



As in the last test, 2 days before, I first piled up the sand within an 

 inch of the top of the opening. Time for entrance: 2 minutes. 



I next piled up the sand so as to completely cover the opening. Finally, 

 after 38 minutes of random movement, while attempting to poke his head 

 through the wire mesh above the opening, he accidentally poked bill and 

 head through the sand pile. Withdrew his head, walked round and round 

 the cage as before, then came back to the hole and poked his head into 

 it six or eight times. This was done apparently simply to get nearer the 

 tgg. Success at end of 40 minutes froiu the bcginniiip- of the test. He 

 went to the nest and sat down. Apparently the nest did not suit him as 

 regards depth, for he immediately began to hollow it out by scratching. 

 Apparently the scratching impulse arises only when the bird is at the nest. 

 I think it exceedingly curious that this reaction was not utilized in stich 

 situations as the above. No further tests were made on him that dav. 



Two days later I again took up work with him. T first tested him with 

 the sand left one inch from the top of the opening. Time: 0.20 minute. I 

 next covered entrance over completely. Result : Aeain many useless move- 

 ments similar to the ones already described. Time : 7 minutes. 



I repeated this. Almost no useless movements. Bird dived at once for 

 the opening, made a small hole, pulled his head out, ran half way round 

 the box and returning squeezed through the opening. Time : 0.66 minute. 



Exactly the same procedure was followed with reference to the female 

 with results identical, except that the female uniformly required more time 

 to make the adjustments and was not so active and eager in her move- 

 ments. From these experiments I concluded (i) that the egg and nest 

 locality may be used in the place of food as a stimulus to the formation of 

 new habits; (2) that the sooty tern can form associations by the trial and 

 error method. 



Experiment III. 



After the above tests had been completed I tried the effect of placing 

 the opening of the box in the other cardinal positions (no obstructions being 

 placed to the opening). It must be remembered that all the adjustments 

 of the bird had been made with the opening facing w-est. The opening 

 was new turned due north. 



Results: The bird (male) on returning went immediately to the west, 

 stood for a second and then walked to the south ; went back to west, then 

 went to the east, then back again to the west, then went north. The 

 moment he saw the opening he went into it and covered the egg. Time : 

 0.96 minute. Second trial : Alighted on west, but ran immediately to north. 

 Time: 0.08 minute. Third trial: Bird alighted on south, swerved sliglith' 

 toward the west, but ran imiuediately tci the north and entered. Time: 

 o.io minute. 



The opening was then made to face east. Bird alighted at south, went 

 to north by way of w-est, paused at north, then seeing door to the east 

 dashed into it. Time, o.io minute. Second trial: Alighting south, ran to 



