178 The Migration of Birds 
thing for us to think about. This question concerning 
the cause of migration is often answered to the satis- 
faction of many by the statement that “The old birds 
lead the way, and the young follow.” If this is a 
logical answer, how are the believers of this theory 
to account for the fact that sometimes the young of 
certain species go first; also how would they account 
for the restlessness during the migration season of 
caged birds that were taken from the nest before they 
could fly? 
THe OricInN oF Micration. Why do _ birds 
migrate? This is a fascinating subject and one much 
indulged in by bird students, probably for reasons 
known to themselves, but apparently because each has 
a pet theory that the others cannot disprove. General 
statements concerning migration may stand approved, 
but when we consider the details of the subject, it 
is easy to ask questions which it is impossible to 
answer. Whatever theories may be advanced in ex- 
planation of migration, it should be remembered that 
birds are very conservative and habits once formed 
may be maintained for ages, though they ceased long 
ago to be useful. Therefore in considering the origin 
of migration we cannot expect to find it wholly in the 
present condition, but we must at least go back to 
a time before the Glacial period. 
