54 Twelve Months With 



the very existence of the species depend, over- 

 comes all other desires, and the bird grows restless 

 and, guided by the hereditary instincts mentioned, 

 it seeks its breeding area. 



Wanderings in search of food or in response 

 to the sex impulse might, of course, lead in any 

 direction, and be entirely aimless, as originally 

 they doubtless were, but, following the course 

 most obviously to their advantage, the birds now 

 usually travel south in search of food, and north 

 in search of home, and these journeys have grad- 

 ually been extended until they now cover hundreds 

 of miles over both land and sea. 



Some very interesting facts have been definitely 

 ascertained with reference to the height that birds 

 attain during migration, and the speed and dis- 

 tances traveled. Birds, in migrating, often ascend 

 to great heights, for which two principal reasons 

 have been assigned: first, that it increases the range 

 of vision, and, second, that they thereby reach a 

 zone or stratum of atmosphere in which flight may 

 be more easy. In 1888 Dr. Frank M. Chapman 

 published an account of certain observations made 

 by him, in which he calculated that the birds 

 traveled at heights varying from 600 to 15,000 

 feet. A number of the birds which he observed 

 were seen flying upw r ards, crossing the moon there- 

 fore diagonally, "these evidently being birds which 

 had arisen in our immediate neighborhood, and 

 were seeking the proper elevation at which to 



