36 



Birds — Conquest or tne Air 



Mastery of the Air. Birds are the only animals that have mastered the air. 

 Human flight is a mastery of machines. Compared with the flights of birds 

 those of insects are little and near the earth — cautious, fair weather travels; 

 even those of bats with their sure piloting by supersonic echoes are specialized 

 and limited. Birds swing into the air with certainty. The golden plover takes 

 off on an over-sea journey of 2000 miles; geese have been seen flying at a 

 height of 9000 feet; by slight turns of body and wings hawks ride on the air 

 currents; bobolinks sing as they fly skyward, then drop, tumbling almost to 

 the earth with the showmanship of an aviator. Birds travel by day and by night, 

 in soft weather and through wind above rough seas. They are the world's 

 greatest migrators (Fig. 36.1). 



Birds are animals that have feathers. Their power and skill in flight, their 

 steering and balancing all depend upon feathers. They are protected from cold 

 and water by feathers dressed with oil; the ear openings of diving birds, 

 American loons and Antarctic penguins swimming under water, are roofed with 

 mats of oily feathers (Fig. 36.2). 



Birds are the warmest of all animals. They have a usual temperature of 

 100° F to 110° F; that of mammals rarely exceeds 98° F to 100° F except 

 under special conditions. In accord with the body temperature, the rate of their 

 metabolism is high. The bodily activity of birds is rapid; their metabolic 

 build-up and use-up is swift. They eat relatively enormous amounts of food, 

 digest it quickly, and eliminate the waste frequently. The prompt use of 

 digested food is aided by oxygen from the air in the air sacs as well as in the 

 lungs. 



The largest living birds are the ostriches (Struthis camelus) that may be 

 7 feet tall and weigh 300 pounds. The condors (vultures) of North and South 

 America have a wingspread of 10 feet. The smallest bird is Helena's humming- 

 bird of Cuba; it weighs one-tenth of an ounce. The bodies of birds are wedges 



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