THE TUBE-NOSES 189 



only meet at the nest for a few hours during the change-over. The 

 incoming bird is usually plump and glossy from the exercise and feeding 

 at sea, while the outgoing bird with an empty stomach is light to 

 handle, stained with long contact with the earth and dirt of the burrow, 

 and anxious to escape to sea in order to break its fast. The fulmar 

 incubates in spells of up to four days (Richter, 1937). 



The following are the available records of the average incubation 

 and fledging periods of the petrels: 



Incubation Fledging 

 Manx shearwater (Lockley, 1942) 

 Little shearwater (Glauert, 1946) 

 Great shearwater (Rowan, 1952) 

 Storm-petrel (Lockley, 1932) 

 Leach's petrel (Gross, 1935) 

 Wilson's petrel (Roberts, 1940) 

 Frigate-petrel (Richdale, 1943) 

 Fulmar (Fisher, 1952) 



These figures show that the petrels have much longer incubation 

 and fledging periods than other birds of comparable size. 



The chick is free of the o^gg forty to eighty hours after chipping. 

 The empty shell is usually ignored, and may be trampled into the 

 nest. The chick is covered with down; it is small, often blind (storm- 

 and Wilson's petrels) and so weak-necked that it cannot hold up its 

 head at first, but rests with the bill touching the ground. One parent 

 usually broods it continuously for about seven days, in its incubation- 

 patch, as if it were an tgg. During the first forty-eight hours it is fed 

 frequently, small doses at a time, by the brooding adult, but later the 

 number of meals is reduced. The semi-liquid oily food is regurgitated 

 and at first held in the throat of the adult, whence it is "dribbled" 

 down to the feeble chick reaching upwards with its bill. As the chick 

 grows stronger it learns to feed more vigorously; the growing bill 

 becomes too awkward to insert wholly into the mouth of the adult. 

 The amount of food rapidly increases with each meal, and the chick 

 now "inserts its bill crosswise into the parent's with its gape pressed 

 firmly against that of the adult. The chick's lower mandible, which 

 is shaped like a trough, is pushed up against the top of the tongue 

 of the adult bird, the tip being well below the chick's bill. The parent 

 now reduces the opening of its throat . . . and semi-liquid is forced 

 through, in fire-hose fashion, into the chick's trough, which has an 

 upslope, and down the neck. While the chick is feeding its lower 

 throat and mandible keep vibrating rapidly. The small opening of 



