THE MYSTER Y OF MIGRATION 205 



in the case of some species on certain routes of 

 migration, where the flocks of species as different 

 as chaffinches and cranes, pass on in such quick 

 succession that the flocks are always in sight, while 

 the lateral width of the travelling multitude feels 

 the way, like a fleet extended over a great width 

 of sea. But this does not account for the safe 

 passage of isolated species to lonely spots, such as 

 the crossing of the Wheatears from Cape Finisterre 

 to the South of Ireland. The assumption that migra- 

 tion is due to a mere automatic impulse guided by 

 experience, does not take into account the conscious 

 end proposed by many birds as the object of their 

 journey. The sentimental motive which induces 

 many birds to seek the old nesting place, is one of 

 the strongest factors in migration. Without some 

 such eager desire, those birds which have once faced 

 the dangers of one journey might refuse to persevere 

 in a second, or to call to their aid those astonish- 

 ing faculties which direct their path. To conclude 

 that, because a domestic species of homing-pigeon 

 performs its flights better after experience, the 

 Australian cuckoo, which traverses a thousand miles 

 of open ocean to nest in New Zealand, or that the 

 midnight flights of birds so tiny as the golden- 

 crested wrens across the North Sea are guided by 

 experience alone, is too hasty and imperfect a 



