460 ON THE OCCURRENCE OF AMERICAN BIRDS IN EUROPE. 
migrations; for the above feat was accomplished by an individual 
hatched and reared in at least semi-confinement, whose powers of 
flight consequently could not be nearly so well developed as in a bird 
grown up wild and free, which nearly every hour of his life has to 
depend on the utility of its wings, either for the purpose of over- 
taking its prey, or for that of escaping from being caught. 
Laying down, therefore, 100 geographical miles per hour as the 
rate of flight of birds during distant migration, one keeps—after the 
above—quite within safe bounds, and, at this rate, the 1600 geogra- 
phical miles from Newfoundland to Ireland would be effected in sixteen 
hours. No ornithologist will doubt for a moment the capability of a 
healthy bird to sustain a flight of that duration; during the long 
summer days many of the Hirundinide are on the wing for as long a 
period, and although their flight may be interrupted by occasional 
rests of very short duration, it is performed in the lower, less buoyant 
atmosphere, and consists of so many evolutions, that most decidedly 
it must on the whole be much more tiresome than the straight path, 
in the pure upper regions, of a bird bent on the performance of one 
long pilgrimage. 
Even supposing that birds become exhausted before accomplishing 
the passage across the ocean, observations I have made in the vicinity 
of this island have fully convinced me that small birds, such as 
Thrushes, Buntings, Finches, &c., are able to rest on the sea—even 
when a little in motion—and afterwards to resume and pursue their 
flight with fresh vigour. Of this I shall give the particulars further 
on; but, for the present, return to the above question, by giving an 
instance of endurance on the wing of a species which, with pretty 
good certainty, may be said every spring to perform in the period of 
one night, a flight of more than 1200 geographical miles; namely, 
from Egypt to Heligoland—the bird in question being a particular 
form of Blue-throated Warbler, Sylvia cerulecula, Pallas. 
This pretty little bird, noted not at all either for rapidity or great 
endurance of flight, has its summer quarters in the high northern 
latitudes of Sweden, Finland, and Siberia, whereas during the winter 
months it is staying principally in Egypt. On its spring migration, 
which takes place during the earlier half of May, the first place 
north of Egypt where it is to be found with certainty in pretty con- 
siderable numbers is Heligoland. Nowhere in the whole intermediate 
distance is it met with but as a great rarity—not even on the neigh-. 
