THE TURKEY 81 



of them rarely come to land except to breed. The well- 

 known stormy petrels, called by English sailors " Mothei 

 Carey's chickens," are not much larger than swallows, 

 yet they will accompany a ship on its course for many 

 days. Every one has heard of the albatross, and the 

 frigate bird is also widely known. Both of these birds 

 possess wings of enormous length, and the former is 

 celebrated for its power of sailing in the breeze without 

 once napping its wings, till the observer is tired of watch- 

 ing it. 



But the mode of life of a great number of birds forces 

 them to execute the most extensive journeys. They 

 have a persistent habit of departing toward the approach 

 of winter from their colder quarters to seek warmth and 

 more abundant food in other climes. This is " migra- 

 tion," and migrating birds always breed in the coldest 

 parts they visit, whether in the northern or in the 

 southern hemisphere. Little, however, is known of 

 migration in the more southern regions of the globe, 

 and the Antarctic lands are so extremely cold that they 

 are not visited as are the lands toward the extreme 

 north. 



When the time of the autumn migration arrives, it is 

 the young birds which, in spite of their inexperience of 

 the route, set out first, save that an old bird will some- 

 times take it into its head to start before the regular 

 time comes, but on the return journey the youngsters 

 generally lag behind. 



Thus locomotion of an extraordinary kind is habitual 

 with birds locomotion both rapid and prolonged, and 

 effected by persistent reiterated strokes of the wings 

 against the resistance which the atmosphere opposes to 

 their efforts. These efforts are also made by the help 

 of vigorous bones and muscles, and a flying bird falls 



