THALASSOGERON CAUTUS. 



when on the nest can only be removed with considerable difficulty or force. 

 While one bird is sitting the other keeps it company by cackling and rubbing 

 its bill against that of its mate, or at the approach of an intruder both protest 

 loudly, spread their tails, and stretch out their heads and bow first one side then 

 on the other. 



This species is singularly dependent on the wind, and in calm weather is liable to 

 be captured in any depression of the ground, for without a strong wind it cannot rise, 

 and in order to fly it must reach the edge of a cliff or prominence and start with a 

 downward movement. During a gale these birds are equally helpless, for they cannot 

 fight against it, and are unable to alight without great difficulty at any given spot, and 

 may be seen making many vain attempts before they succeed in achieving 

 their object. 



Like most other Petrels, this species possesses the habit of ejecting a foetid oily 

 substance through the nostrils. 



The nest is composed of chocolate coloured soil mixed with small roots and other 

 vegetation, and is usually placed under thick matted grass or in a sheltered recess 

 under a rock. 



The egg is laid early in October and fits into a longitudinal depression, bare of 

 feathers below the breast-bone of the parent bird, and is thus kept warm. When the 

 bird stands up in the nest the egg is quite concealed, but if it moves about the egg is 

 dropped. The eggs are more or less freckled with reddish-brown markings at the 

 larger end. 



The external diameter of the nest is about 14 inches, height 5^ inches. The bird, 

 according to Mr. D. le Souef, measures from tip to tip of its wings 8 feet (Ibis, 1895, 

 p. 414). 



Adult. General colour above slaty-brown, the mantle and back clear slaty-grey, 

 with dusky brown edges to some of the feathers, which have white bases, causing a 

 mottled appearance ; lower back, rump, and upper tail-coverts pure white ; scapulars 

 dark slaty-grey, blackish towards the ends, especially the longer ones ; wings dark 

 brown marked with slaty-grey, the lesser and median, as well as the greater, coverts 

 with concealed white shafts and white bases to the feathers, the distal ends blackish- 

 brown, with a subterminal shade of dark slaty-grey ; quills blackish, white for the 

 greater part of the inner web of the primaries and outer secondaries, which also show a 

 certain amount of slaty-grey ; the outer primaries with yellow shafts ; inner secondaries 

 slaty-brown, white for two-thirds of the inner web, and mottled with black near 

 the base of the outer web ; tail slaty-grey, browner on the outer webs and 

 towards the ends ; crown of head and neck all round, as well as the under- 

 surf ace of the body, white ; under wing-coverts and axillaries as well as the quill- 

 lining white ; on the sides of the face a slight tinge of grey, a blackish streak passing 

 through the eye to above the ear-coverts ; bill light vinous-grey or bluish horn-colour, 



349 



