xvi INTRODUCTION. 
cellular matter, and at no season of the year are the true birds 
of passage so fat as at the approach of their migration. The 
Gulls, Cranes, and Herons, almost proverbially macilent, are at 
this season loaded with this reservoir of nutriment, which is 
intended to administer to their support through their arduous 
and hazardous voyage. With this natural provision, dormant 
animals also commence their long and dreary sleep through 
the winter, —a nutritious resource no less necessary in birds 
while engaged in fulfilling the powerful and waking reveries of 
instinct. 
But if the act of migration surprise us when performed by 
birds of active power of wing, it is still more remarkable when 
undertaken by those of short and laborious flight, like the 
Coots and Rails, who, in fact, perform a part of their route on 
foot. The Great Penguin (A/ca impennis), the Guillemot, and 
the Divers, even make their voyage chiefly by dint of swim- 
ming. The young Loons (Colymdus glacialis), bred in inland 
ponds, though proverbially lame (and hence the name of Lom, 
or Loon), without recourse to their wings, which are at this 
time inefficient, continue their route from pond to pond, 
floundering over the intervening land by night, until at length 
they gain some creek of the sea, and finally complete their 
necessary migration by water. 
Birds of passage, both in the old and new continents, are 
observed generally to migrate southwest in autumn, and to 
pass to the northeast in spring. Parry, however, it seems, ob- 
served the birds of Greenland proceed to the southeast. This 
apparent aberration from the usual course may be accounted 
for by considering the habits of these aquatic birds. Intent on 
food and shelter, a part, bending their course over the cold 
regions of Norway and Russia, seek the shores of Europe ; 
while another division, equally considerable, proceeding south- 
west, spread themselves over the interior of the United States 
and the coast and kingdom of Mexico. 
This propensity to change their climate, induced by what- 
ever cause, is not confined to the birds of temperate regions ; 
it likewise exists among many of those who inhabit the tropics. 
