The Behavior of Noddy and Sooty Terns. 223 



acterizc it after the egg is laid (see p. 201). I found that hy putting an egg 

 in the nest of such a " laying " noddy, I could change its habits from those 

 of a " layer " to those of a "' sitter." One can observe under such circum- 

 stances an almost immediate change in the general disposition of the birds. 

 Before the egg is put down in the nest, the bird, which may be sitting on 

 a nearby limb, will fly away at the slightest disturbance. When the egg is 

 put into the nost, the bird on returning will alight near the nest and sit 

 stolidly on a limb as before. Suddenly it is visually stimulated by the egg. 

 It peers down at it, extending the head and withdrawing it, turning the head 

 slightly to one side. It then alights on the nest. Contact with the egg 

 seems immediately to change the disposition of the bird. The bird will now 

 remain upon the nest, " rattling " in its grufif, hoarse way, and attempting 

 to strike if one approaches too near. The reverse of the above behavior can 

 be noticed if the egg is removed from the nest of some bird, even if it has 

 been sitting on the egg for several days and consequently has had exercise in 

 all the instinctive activities present during the brooding-season. 



The sooty reacts quite differently to colored eggs. They were dyed with 

 the same dyes as were the noddy eggs. These tests were made upon three 

 separate parts of the island. The sooties on returning and finding the col- 

 ored eggs exhibited signs of great uneasiness. They walked round and 

 round them, poked them with their beaks, rolled them out of the nest and 

 then rolled them back. In one set of tests the eggs colored with vermilion 

 dye were absolutely rejected. In another set of tests, made with different 

 birds, vermilion was accepted ; green was not accepted in one case, but in 

 two other tests it was accepted. The black tgg was rejected in one case, 

 but was accepted in two other cases. On the whole, each color and black 

 was accepted, but in every set of tests at least one of the dyed eggs was 

 rejected. In one case the bird whose nest contained the vermilion egg dug 

 a new nest alongside of the old one and made nearly 100 trips between the 

 old nest and the new. They, however, accepted each other's eggs and noddy 

 eggs without question. One sooty sat down immediately upon its nest after 

 a hen egg had been put there in place of its own. Several days later, on 

 again examining this nest, I found that the hen egg had been pushed aside 

 and a new sooty (tgg deposited. 



From these experiments on the dyed eggs, it becomes apparent: 



(i) Under the conditions of the above test the noddy is not at all 

 affected by changing the hue, brightness, and markings of its egg. 



(2) The sooty is affected by changing the visual appearance of its egg, 

 but whether in the latter case the disturbance was due to the change in bright- 

 ness or the change in hue or in marking, is not determined by the above 

 experiments. 



(3) Neither the noddy nor the sooty recognizes its own tgg. 



