43^ The Bird 



body between the thighs. Both sexes are provided with 

 this contrivance during the breeding season, and reUeve 

 each other of the burden at intervals. 



" The gull tribe, however, are far more exposed to acci- 

 dent and to enemies, both in adult life and as to their 

 eggs and young, than are the penguins, petrels, and others 

 mentioned above; and here the rule is from two (skuas) 

 to four (gulls and terns) eggs in a nest. When we come 



Fig. 346. — Eggs of Ostrich, Cassowary, Hummingbird, and Hen, 

 showing comparative size. 



to the shore- and marsh-birds — the plovers, snipe, sand- 

 pipers, jacanas, all of which nestle on the ground, usually 

 near the shore of the sea or lakes — we judge them to be 

 exposed to about the average of dangers, since their nest 

 complement is from four to six. The northern, tundra- 

 loving cranes need raise few young, and hatch only two 

 eggs; but when we come to the water-birds — the rails, 

 gallinules, ducks, and geese — we find an extensive group 



