THE LIVING BIRD 7 



day's migration. Many wild birds appear to fly 

 merely for the sake of flying. Thus male white- 

 winged scoters {Oidemia deglandi) in Alberta, on 

 their favorite breeding lakes such as La Nonne, 

 Wabamun, St. Anne, etc., from the middle of June 

 to the end of July take a flight of two to two and a 

 half hours every evening. Their cruising speed is 

 approximately forty miles an hour. For five or six 

 weeks they thus do a daily dozen — mostly in circles 

 round the lake — of some eighty to one hundred 

 miles, or a total in six weeks of about four thousand 

 miles. The same amount of flight directed in a 

 straight line south would place them at the equator, 

 far beyond their normal wintering limits in Florida 

 and lower California. Yet this expenditure of 

 energy takes them nowhere. They finish where 

 they began. It is but a pastime, a congenial 

 method of killing a summer evening. 



The mere production of heat, however, is not 

 sufficient to account for the results. When we talk 

 about a ''warm-blooded" bird or mammal, we are 

 using the careless terminology of everyday lan- 

 guage. What we actually imply is even-tempera- 

 tured, a very different matter for it means not only 

 the production but the conservation of heat. Even 

 reptiles produce heat, but only some (e.g. the fe- 

 male python when incubating eggs) can con- 



