272 BRITISH SEA BIRDS. 
as they fly to and fro and in and out of their nests. 
Then during the period of migration many Martins 
pass along the sea-board, and sometimes the 
observer may be fortunate enough to witness their 
actual arrival from over the sea, or their final depar- 
ture across its lonely expanse. 
ROCK DOVE. 
We here have another exclusively marine species, 
the Columba livia of Linnzus and most modern 
writers, confined to such portions of the coast as 
are precipitous and full of caves and hollows. The 
Rock Dove may be readily distinguished from all 
the other British species of Pigeons by its white 
lower back and rump, and strongly-barred wings. 
As may naturally be inferred from the cliff-haunting 
propensities of this Dove, it is practically absent 
from the low-lying eastern coasts of England, local 
on the south coast, but becomes much commoner 
further north and west, where the cliffs are rugged 
and lofty, and full of those wave-worn hollows and 
fissures that are the Rock Dove’s delight. As most 
readers may be aware, this species is the original 
stock from which the numerous races of dovecot 
Pigeon have descended. Curiously enough, this 
bird is inseparably attached to the coast; it is a 
rock-haunting species, and one which rarely or 
never perches in trees. Usually our first acquaint- 
ance with the Rock Dove is made as the startled 
bird dashes out of the cliffs, with rattling wings and 
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