The Migration of Birds 187 



night. Excellent examples are the Robin, Horned 

 Lark, and most Icteridae (BoboUnk, Blackbird, and 

 Orioles). 



"Birds of easy, tireless wing, which habitually feed 

 in the air or over very extensive areas, migrate exclu- 

 sively by day, because, being able either to obtain 

 their usual supply of food as they fly, or to accom- 

 plish the longest journeys so rapidly that they do not 

 require to feed on the way, they are under no neces- 

 sity of changing their usual habits. The best examples 

 are Swallows, Swifts, and Hawks." 



Storms or foggy weather interfere seriously with 

 the flight of birds, — ^this being particularly true' of 

 the night-flying varieties. There are natural high- 

 ways along which birds travel, such as the coast line, 

 mountain ranges, or river valleys, and on clear nights 

 these are probably discernible, while under unfavor- 

 able conditions progress is slow and doubtless many 

 lose their way. Unless one has carefully observed, it 

 does not seem possible that birds travel in such vast 

 numbers at night. Their flight through the darkness 

 during migration may be compared to the flight of 

 pigeons, so common in this section of the United 

 States fifty years ago. The telescope has greatly 

 aided in ascertaining this, as well as in revealing the 

 fact that birds fly at a very great height, some species 



