MIGRATION OF BIRDS 319 



which they cannot overcome, warns them that the 

 hour for their departure is drawing near. 



"If one desires to witness this anxiety that tor- 

 ments the bird when the time for migrating arrives, 

 he may do so by rearing in captivity a migratory 

 bird caught very young. The captive, though never 

 having lived with its kind or had any knowledge of 

 their migratory habits, and furthermore having 

 been kept in a cage with no experience of cold or 

 hunger, nevertheless, when the season for flitting 

 arrives, shows agitation and mental distress, and 

 tries to escape from its prison — after remaining so 

 quiet and contented up to that time. Some inner 

 voice — instinct we call it — says it is time to go, and 

 the captive is eager to be off. If the desire is 

 thwarted, death follows. 



"To tear oneself from beloved haunts to incur the 

 fatigues and perils of a long journey is undoubtedly 

 a painful decision ; yet the bird courageously submits 

 to the inevitable, but in the hope of coming back 

 again some day. The strong reassuring the weak, 

 the older ones guiding the young, the departing flock 

 forms itself into a caravan and takes wing for the 

 south. The sea is crossed, the treacherous sea from 

 which, at long intervals, rises an island as halting- 

 place. Many perish in the crossing, many reach the 

 goal worn with hunger and spent with fatigue. 



"The day for starting on this momentous journey 

 is decided upon in a great assembly, toward the end 

 of August for the window-swallow, and considerably 

 later, even as late as November, for the chimney- 



