INTRODUCTION. 
xliii 
after rearing their young. Some are so given to wandering 
that their choice of a country is only regulated by the resources 
which it offers for subsistence ; such are the Pigeons, Herons 
of several kinds, Snipes, wild Geese and Ducks, the wandering 
Albatros, and Waxen Chatterer. 
The greater number of birds travel in the night ; some 
species, however, proceed only by day, as the diurnal birds of 
prey, — Crows, Pies, Wrens, Creepers, Cross-bills, Larks, Blue- 
birds, Swallows, and some others. Those which travel wholly 
in the night are the Owls, Butcher Birds, Kingfishers, Thrushes, 
Flycatchers, Night Hawks, Whip-poor-wills, and also a great 
number of aquatic birds, whose motions are also principally 
nocturnal, except in the cold and desolate northern regions, 
where they usually retire to breed. Other birds are so pow- 
erfully impelled by this governing motive to migration that 
they stop neither day nor night ; such are the Herons,- Mota- 
cillas. Plovers, Swans, Cranes, Wild Geese, Storks, etc. When 
untoward circumstances render haste necessary, certain kinds 
of birds, which ordinarily travel only in the night, continue 
their route during the day, and scarcely allow themselves time 
to eat ; yet the singing- birds, properly so called, never migrate 
by day, whatever may happen to them. And it may here be 
inquired, with astonishment, how these feeble but enthusiastic 
animals are able to pass the time, thus engaged, without the 
aid of recruiting sleep ? But so powerful is this necessity for 
travel that its incentive breaks out equally in those which are 
detained in captivity, — so much so that although during the 
day they are no more alert than usual, and only occupied 
in taking nourishment, at the approach of night, far from seek- 
ing repose, as usual, they manifest great agitation, sing without 
ceasing in the cage, whether the apartment is lighted or not ; 
and when the moon shines, they appear still more restless, as it 
is their custom, at liberty, to seek the advantage of its light 
for facilitating their route. Some birds, while engaged in their 
journey, still find means to live without halting, — the Swallow, 
while traversing the sea, pursues its insect prey; those who 
can subsist on fish without any serious effort, feed as they pass 
