THE WORLD'S BIRDS. 51 



FORM. Bill variable in form, but generally of medium 

 length, and flat-sided, with nostrils slit-like and 

 generally far forward, corner of mouth below eye ; 

 feet with shanks of variable length, front toes 

 usually fully webbed, though in some the webbing 

 is very slight ; hind- toe usually very small. Wings 

 long and pointed ; tail moderate or long. Head 

 large, and body light. 



PLUMAGE AND COLOURATION. Colouration usually 

 showing much white in adults ; no sex-difference, but 

 often a seasonal change. Young usually mottled 

 brown, and very unlike adults. Beak and feet 

 usually bright-coloured. 



YOUNG. Downy and rather active, but the food is 

 disgorged for them by their parents, though they 

 can pick it up. Their down is usually grey, with 

 dark spots. 



NEST. A loose, open structure of sticks, sea-weed, 

 etc., placed on the ground, on rock-ledges, or on 

 trees and bushes. 

 EGGS. One to four ; spotted. 

 INCUBATION. Three to four weeks. 

 COURTSHIP. Very demonstrative, the male arching 

 his neck, or lowering it with the head turned up, 

 and opening his wings at the pinions, while keeping 

 them closed at the tip. 



FOOD. Fish, and other marine animals ; carrion, 

 mice, insects and berries are eaten by many 

 species ; they also often eat the eggs and young 

 of other birds. Indigestible substances are dis- 

 gorged as " castings." 



GAIT. The typical gulls walk easily and gracefully, 

 but some of the short -legged Terns waddle, and 

 walk but little. They swim lightly, but hardly 

 any can dive. Many of them perch on trees. 

 FLIGHT. Slow, but graceful, and long-sustained. The 

 Skuas and Noddies fly with quicker strokes. 



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