THE INSURGENCE OF LIFE 169 



recall Audubon's observation in reference to the Rice 

 Bird, Dolichonyx oryzivora, that it flies in Spring by night, 

 and in Autumn by day. 



Another general fact that impresses us in regard to 

 migration is its regularity and success. When weather 

 conditions are very unpropitious, there is often great 

 mortality. The streets of towns are sometimes strewn 

 with the corpses of thousands of birds that have gone 

 astray and succumbed to the cold. As many as five 

 hundred nightingales have been gathered in a single day 

 from one small town. Large numbers of migrants perish 

 every year by dashing themselves against the windows of 

 lighthouses. But, on the whole, the striking fact is not 

 the number of failures but the large proportion of successes. 

 This is the more striking when the difficulties of a long 

 migration- journey are borne in mind. What we are made 

 to feel is that migrating is an old-established business ; 

 it has been going for so many hundreds of thousands of 

 years that it has acquired a certain smoothness. A thrush 

 born in the North of Scotland was found at the end of its 

 first summer near Lisbon a long journey for an inex- 

 perienced traveller who is hardly counted as a migrant 

 at all. And there are many similar instances. 



The feature of regularity is also illustrated by the re- 

 markable punctuality of arrival and departure which is 

 usually exhibited, except, indeed, when the meteorological 

 conditions are unusual. Fog and head-winds may delay 

 arrival ; a summer that has favoured the increase of insect 

 life may induce birds to postpone their departure ; but, 

 on the whole, there is a remarkable temporal regularity 

 in the comings and goings. 



While there is great regularity in many cases, it must 



