The Behavior of Noddy and Sooty Terns. 221 



nest and covered egg (mate being absent). Both the noddies and the sooties 

 in the vicinity of this nest were badly frightened by this bird. The mate on 

 returning flew round and round the nest, but would not alight near it. The 

 mate would circle out over the water and then back to the nest. Finally 

 the unmarked bird alighted near the nest and fought off an intruder. The 

 unmarked bird sat near the nest, but made no attempt for a long time to 

 take its turn upon the egg. The marked bird became restless under these 

 circumstances. It would hop up and expose the egg, turning round and 

 round and make signs by nodding the head to the passive mate sitting 

 nearby. The mate made tentative efforts to approach closer to the nest and 

 seemed almost persuaded to take its turn, but the relief was not finally 

 effected until 3 hours had passed. 



These two tests as they stand prove nothing definitely. They only sug- 

 gest that any change in the visual appearance of the birds breaks down the 

 customary and habitual responses which take place between birds attached to 

 a single nest.^ It occurred to me afterwards that since the noddy has be- 

 come accustomed to the appearance of the sooty, it would have been a more 

 reliable test had I painted the noddy in the guise of the sooty. The vivid 

 red. if the birds sense color-tone (or even the changed brightness) obviouslx- 

 might have been exciting and might have aroused fear. It is just possible 

 that if I had modified the appearance of the two noddies by painting them 

 with different shades of gray that the change in the visual appearance might 

 not have been noticed by the mates on their return. 



TESTS WITH SOOTIES AS TO RECOGNITION BETWEEN MATES. 



A similar test was made upon the sooty. Two birds were captured at 

 marked nests, the night before the day upon which the tests were to be 

 made. The white throat, breast, and spaces between the eyes of sooty No. 

 I were completely covered with burnt sienna (in oil). Sooty No. 2 was 

 painted as No. i, but with permanent blue instead of burnt sienna. 



Sooty No. I.- — Mate on egg. Marked bird tried to alight. All the 

 sooties nesting in the vicinity flew up, raising a tremendous uproar. The 

 bird alighted within a foot of its nest. Its mate and all the other sooties 

 nearby drove the bird away from the nest vicinity, striking it violently with 

 their beaks. It flew away, but returned in 8 minutes. While in the air it 

 called to the mate (still upon the nest), mate got on feet, answered the 

 call, showing evident signs that the call was recognized. Marked bird again 

 alighted within a foot of nest. Violent commotion was again raised in the 

 colony. Mate struck the marked bird violently with the beak and drove it 

 away. Marked bird tried several other times to alight near the nest, but 

 this was not permitted. Wherever in the whole island this bird tried to 

 alight, commotion was aroused. It then disappeared from the island, after 

 vainly trying for 3 hours to approach the nest. It did not appear again 

 that day in the vicinity of its nest. The following morning, however, the 

 marked bird was calmly brooding the egg. 



' There is a possibility, too, that the disturbance might have been due partially 

 at least to the olfactory characteristics of the dyes. 



