262 POULTRY AND WILD BIRDS 
in the spring, accomplishing each time a journey of 8000 
miles. Some Snipe and Plover belong to this class of tourists. 
The Journey and its Risks. — These marvelous journeys 
are not accomplished without great hazard. In fact, migra- 
tion keeps the bird population thinned; all the weak and the 
foolish perish by the way, and we have only “ the survival of 
the fittest.” Most birds travel in the early part of the night 
— from about eight to eleven or twelve o’clock. They rest 
the remainder of the night, and feed and rest the next day. 
Geese and other birds with good wings fly either by night or 
day and can travel many hours in succession. The birds 
fly from half a mile to a mile or more high, following the direc- 
tion of streams, mountain chains, and other landmarks. 
They usually travel in great flocks, the old ones leading the 
way, and they keep together by calling to each other as they 
fly. The instinct exhibited in migration is truly wonderful; 
but it is not infallible, and birds sometimes become separated 
from their companions and lose their way. 
Cause of Migration. —It is popularly supposed that birds 
go south in the fall to escape cold weather. While this may 
be one of the causes of migration, especially in case of those 
who stay till cold weather really approaches, it does not explain 
why some species, as the Kingbird, start as early as July or 
August, — as soon as the young are hatched and grown strong 
enough. The fact is that the majority of the birds leave 
before the cold furnishes a reason. As soon as insects become 
scarce, the birds that do not relish other kinds of diet betake 
themselves to more sunny climes; and for this reason it is 
considered that food supply is a more fundamental factor than 
temperature. 
But if we ask why they come north again in the spring, 
we have an even more difficult question. Probably we may 
