INTRODUCTION, xli 
sive voyages, are sedulously employed ; and hence, at certain 
seasons, when they are usually in motion, we find their arrival 
or departure accelerated by a favorable direction of the winds, 
That birds also should be able to derive advantage in their 
journeys from the acuteness of their vision, is not more wonder- 
ful than the capacity of a dog to discover the path of his 
master, for many miles in succession, by the mere scent of his 
steps. It is said, indeed, in corroboration of this conjecture, 
that the Passenger, or Carrying Pigeon, is not certain to return 
to the place from whence it is brought, unless it be conveyed 
in an open wicker basket admitting a view of the passing 
scenery. Many of our birds, however, follow instinctively the 
great valleys and river-courses, which tend towards their 
southern or warmer destination; thus the great valleys of 
the Connecticut, the Hudson, the Delaware, the Susquehanna, 
the Santee, and more particularly the vast Mississippi, are often, 
in part, the leading routes of our migrating birds. But, in fact, 
mysterious as is the voyage and departure of our birds, like 
those of all other countries where they remove at all, the des- 
tination of many is rendered certain, as soon as we visit the 
southern parts of the Union, or the adjoining countries of Mex- 
ico, to which they have retired for the winter; for now, where 
they were nearly or wholly unknown in summer, they throng 
by thousands, and flit before our path like the showering leaves 
of autumn. It is curious to observe the pertinacity of this 
adventurous instinct in those more truly and exclusively insec- 
tivorous species which wholly leave us for the mild and genial 
regions of the tropics. Many penetrate to their destination 
through Mexico overland; to these the whole journey is 
merely an amusing and varied feast. But to a much smaller 
number, who keep too far toward the sea-coast, and enter the 
ocean-bound peninsula of Florida, a more arduous aerial voy- 
age is presented; the wide ocean must be crossed, by the 
young and inexperienced as well as the old and venturous, 
before they arrive either at the tropical continent or its scat- 
tered islands. When the wind proves propitious, however, 
our little voyagers wing their unerring way like prosperous 
