204 THE VOYAGE OF H.M.S. CHALLENGER. 



were approached. Only three species occur on them, two noddies and a booby. The 

 Noddies (Anous stolidus and Anous melanogenys) are small terns or sea swallows, black 

 all over, with the exception of a small white patch on the head. The Booby (Sula 

 leucogastra) is a kind of gannet ; the full-grown birds are white on the belly, with a 

 black head and throat; the black ending on. the neck, where it joins the white in a 

 straight conspicuous line ; the back is dark. The younger birds are brown all over. 

 A few of both birds soon came off to have a look at the ship as she approached the rocks. 

 On landing, the rocks were found to be covered with noddies and their nests, some 

 containing eggs, whitish in colour, with red spots at the larger end, and others with 

 young in them, little round balls of black down. The air was full of noddies and boobies 

 circling about, and screaming in disgust at the invasion of their home. 



The noddies' nests are made of a green seaweed (Caulerpa clavifera) which grows on 

 the bottom in the bay and around the rocks, and which, getting loosened by the surf, 

 floats, and is picked up by the birds on the surface of the water. The weed is cemented 

 together by the birds' dung, and the nests, having been used for ages, are now solid 

 masses, with a circular platform at the summit, beneath which hang down a number of 

 tails of dried seaweed. The older nests, placed on the faces of the cliffs, project from 

 the sheltered sides of the rocks, like brackets, having been originally commenced, 

 as may be seen by the complete series of gradations existing, by a pair of birds laying 

 an egg on a small projecting ledge of rock and adding a few stalks of weed. A series of 

 these nests are seen in the photograph (PI. III.), appearing like white patches on the per- 

 pendicular surface of the low cliff. If these white patches be closely examined, each 

 will be seen to represent a bracket-like nest with dependent fringe, and in most cases to 

 have a black noddy with a conspicuous white patch on its head sitting on it. A greater 

 number of the noddies, however, place their eggs on the bare flat rocks in any slight 

 hollow or chink. The two species of noddy are so nearly alike that it was not noticed 

 during the stay of the Expedition that more than one was present, and it appeared as 

 if, the cliff surface on the rocks being limited, only the stronger noddies were able to 

 maintain their position in the bracket-like nests, whilst the weaker had to put up with 

 the more exposed open rocks ; but probably more careful examination would have shown 

 that the bracket-like nests of seaweed belonged to one species of Anous only and the bare 

 nests of the horizontal rocks to the other. A white peak on the western side of the 

 bay forms the home of the boobies, which are not nearly so numerous as the noddies, 

 and seem to be almost restricted to this one peak, out of the five of which the rocks 

 are made up. 



The whiteness of the rock is caused by the birds' dung, which in some places forms 

 on the rocks, as described by Darwin, an enamel-like crust, which is hard enough to 

 scratch glass. Some of this was found at about 45 feet above sea level. The rock is 

 steep on the sheltered sides, and is there hung all over with the bracket-like nests of 



