^"^ioif ^^] Gross, The Yelloiv-billed Tropic-bird. 57 



spotted with three colors : chestnut, chocolate brown, and purplish 

 red. The spotting is usually more dense at the larger end and 

 quite often presents a blotched or smeared appearance (Plate VI, 

 fig. 8). On other specimens the distribution of markings is more 

 uniform, there being no predominance of color at the larger end 

 (Plate VI, fig. 7). 



The chocolate color is easily rubbed off, especially when the egg 

 is first immersed in water. Even the contact of the bird's body 

 during incubation may remove more or less of the color. 



The measurements of 8 eggs collected form various parts of the 

 islands are as follows, — 



The incubated egg weighs slightly less than the fresh egg. 



The birds copulate in the recesses of the cliffs and apparently 

 in the niche eventually to be used as a nesting site. At Bethel's 

 Island I found two pairs copulating in different places in the rocks. 

 In one case the female was bleeding about the head from wounds 

 made by the male in his desperate attempts at holding the bird 

 during copulation. Both females presented a somewhat mussed 

 and haggard appearance. During the four days elapsing before 

 the next visit to the island, eggs were deposited in these nests, and 

 in all probability by the females previously observed. Several 

 other pairs of adult birds were found together, but in these cases 

 there was no evidence of copulation and no clew for the identifica- 

 tion of sex. 



Both the male and female birds take part in incubation, and 

 during this period the egg is seldom left uncovered for more than a 

 few minutes. The birds take their turns at the nest, thus giving 

 each other an opportunity to feed. In one case an adult was seen 

 feeding its mate while the latter was brooding the egg. 



