72 A NATURALIST ON THE " CHALLENGER." 



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. I found some of this at about 45 feet above sea level. 



The rock is 50 feet in height, steep on the sheltered sides, 

 and there hung all over with the bracket-like nests of the 

 noddies ; the weather-side slopes more gently ; and all over 

 it, on every little flat space, are the boobies' nests, mere 

 hollows, some containing two eggs, but mostly with one only. 

 The eggs are as large as a fowl's, sometimes dirty- white all over, 

 sometimes blotched with brown. 



In many of the nests were young, which were of all ages ; 

 some just out of the egg, ugly big-bellied black lumps, without 

 a particle of down or feathers ; then larger ones, as big as one's 

 fist, covered with white down ; then others as large as a fowl, 

 thickly clothed with down ; then larger ones again, with brown 

 wing feathers and brown feathers on the breast, the white down 

 remaining only in patches, about the head especially. Then 

 birds with brown feathers all over, full- sized and just beginning 

 to fly. 



Two almost full-grown birds, as big nearly as geese, were 

 having a desperate fight at the bottom of the slope as I came up. 

 They evidently thought each other the cause of the whole 

 disturbance. They fought furiously with their sharp bills, 

 flapping their wings, and half screaming, half croaking, with 

 anger. They fought till they were quite exhausted, and could 

 not stand, but went at it again after they had rested awhile and 

 recovered their breath. 



Some old boobies were sitting on their young on the top of 

 the peak. They would not move until actually pushed off the 

 nest. The young, both of boobies and noddies, are very brave, 

 and scream and strike out hard at anything put near them. Our 

 spaniels could not tackle the young boobies, but after one or 

 two pecks fought quite shy of them ; and even the little noddies 

 kept the dogs pretty well at bay, twisting round in the nests and 

 always showing front. Natural selection has no doubt brought 

 about this bravery in the young, to protect them from their 

 constant enemies, the crabs. 



