THE ALLIES OF THE PIGEON : AVES 391 



separately move off on their long trip. The larger birds, with 

 special means of defense, as the large hawks and cranes or 

 those species with untiring flight, as the ducks, choose day- 

 light in which to travel. Some of the smaller birds which 

 are also rapid and untiring fliers, like the swallows, also 

 carry on their migrations during the day, but most of the 

 smaller birds migrate at night. A foggy night causes the 

 death of large numbers of birds ; over fifteen hundred indi- 

 viduals have been picked up at the foot of Bartholdi Statue 

 in New York Harbor after a dark night in the migration 

 period. Attracted by the bright light the birds had dashed 

 against the glass in their swift flight. Birds are exposed to 

 other dangers on their migration-flight. They are fed upon 

 by other animals, and many perish from fatigue, or are blown 

 out to sea, where they fall exhausted into the water. 



It is not thoroughly understood how birds find their way 

 over such great stretches of territory. The " fly-lines " of 

 some swallows are ten thousand miles long. The golden 

 plover breeds in arctic America and winters in Patagonia. 

 By some ornithologists (students of birds) the ability to 

 travel these great distances is ascribed to the possession of 

 a sixth sense, that of direction, which seems to be pos- 

 sessed by some other animals and by savage man. It is 

 supposed that somehow the nervous system registers the 

 ground passed over. Observations by American ornitholo- 

 gists seem to show that the old birds lead the way. Some 

 birds keep up a continual calling to each other, which may 

 help to keep the members of the flock together. In following 

 their migration-routes birds have undoubtedly been helped in 

 some cases by the rivers and coast-lines, and in Europe there 

 are cases where the fly-lines mark submerged coast-lines which 

 the birds followed when the land was above the water. There 

 is such a line between England and the continent, and another 

 across the Mediterranean Sea. 



