HOW AND WHY DO BIRDS TRAVEL? 18] 
single continuous flight, while others consist of a sort 
of straggling from place to place with stops for food, 
water, or rest. The migration of the same birds may 
differ in this respect at different seasons or different 
stages of the journey. Or different flocks or individ- 
uals may differ much from others in their migrating 
habits for the time. 
Where the flights are long and continuous it fre- 
quently happens that birds go in great flocks or 
streams, some that are solitary at other times being 
very social now. 
Such flights are apt to be at great altitudes, so far 
as to be usually out of sight. Star gazers have seen 
them pass their telescopes in the night (for these 
long flights extend over nights, especially if the 
moon shines), and they are able to estimate by the 
sharpness of the focus how high these bird nebulee 
are. Two, three, and even more miles have been as- 
serted. An observer on a certain island where birds 
rest speaks also of single birds coming down from the 
unseen heights and alighting. 
Often after approaching land and nearing the end 
of the journey, our little birds stop short of home and 
drift up, singing and feeding. Thus we may note the 
loitering of the Peabody sparrow, purple finch, and 
various thrushes, ete. The Baltimore oriole rides up 
on the great spring wave of the opening leaf and ex- 
panding catkin, and the warblers, vireos, ete., wait till 
the full flush of summer is here, and beat northward 
part of the way through tree top and tangle to the 
music of the insect’s gauzy wings. 
