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PRACTICAL ZOOLOGY 



feathers; and a layer of fat just beneath the skin serves to 

 keep in bodily heat. They feed on fishes and other marine 

 animals. On shore they stand erect, side by side. They nest 

 in colonies, laying one or two eggs either among the rocks or 

 in a burrow. 



Water Birds. — It is convenient to divide the seventeen 

 orders of Northern American birds into two groups — water 

 birds and land birds. Water birds are those that live near 



Fig. 242. — Great blue heron spreading its wing. (Photo, by Hegner.) 



ponds and streams or on the seacoast. Most of them spend 

 much of their time swimming about on the surface or wading 

 near shore. Their food consists of water plants, insects, worms, 

 and other small animals captured in the water or extracted 

 from the muddy bottom. 



Diving Birds. — The grebes and loons are called diving 

 birds because of their ability to swim under water. Usually 

 these birds are awkward on land since their bodies are built 

 for swimming and their feet are webbed. 



