INTRODUCTION. 
25 
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 mo- 
tions are often principally nocturnal, except in the cold and desolate 
northern regions, where they usually retire to breed. Other birds are 
so powerfully impelled by this governing motive to migration, that 
they stop neither day nor night; such are the Herons, Motacillas, 
Plovers, Swans, Cranes, Wild Geese, Storks, &c. 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 hap- 
pen 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 seeking 
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 or graze the surface of the deep. If 
the Wren, the Creeper, and the Titmouse rest for an instant on a 
tree to snatch a hasty morsel, in the next they are on the wing, to 
fulfil their destination. However abundant may be the nourishment 
which presents itself to supply their wants, in general, birds of pas- 
sage rarfely remain more than two days together in a place. 
The cries of many birds, while engaged in their aerial voyage, are 
such as are only heard on this important occasion, and appear ne- 
cessary for the direction of those which fly in assembled ranks. 
During these migrations, it has been observed, that birds fly ordi- 
narily in the higher regions of the air, except when fogs force them 
to seek a lower elevation. This habit is particularly prevalent with 
Wild Geese, Storks, Cranes, and Herons, which often pass at such a 
height as to be scarcely distinguishable. 
3 
