The Migration of Birds 187 
night. Excellent examples are the Robin, Horned 
Lark, and most Icteride (Bobolink, 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 
