180 
BIEDS. 
vertical fissure in which to place its nest, never on exposed 
ledges, and only lays two eggs, Mr. Osborne never having 
heard of a single instance when this number was departed 
from (0. MSS., 1868). 
Very common along the whole coast, especially at 
Duncansbay Head and southwards. Also breeding (or 
merely resting ?) on high grassy ledges in the yellow sand- 
stone cliffs of Dunnet, curiously enough, in similar situa- 
tions as those chosen by the cormorants, a most unusual 
departure from their almost invariable habit. 
189. Sula bassana (L.). Gannet, 
An occasional visitant to the east coast, not rare, and old birds 
most abundant. The regular streams of migration of the 
gannets round our islands are worthy of attention, flying 
east and north along the north coast in spring, and flying 
west daily in autumn. Between 2150 and 3080 have been 
estimated to fly westward within view of Cape Wrath dur- 
ing fifteen days noted, between 14th July and 9th August. 
They pass between 7 A.M. and 1 0 p.m. each day, in all winds 
and weathers. (See Migration Report, 1872, p. 41.) 
A common summer visitor to the Caithness coast, but does 
not breed, appearing merely to follow the shoals of herrings 
that abound at that season. " A curious feature in their 
local history is that they are observed invariably to fly in a 
northward direction ; that, while they follow the east coast 
on their journey northward, their return must be effected 
by some other route, as the bird is seldom or never seen on 
the east coast of Caithness to pursue a southward course " 
(H. Osborne in MSS.). 
Their migrations are undoubtedly influenced by those 
of the herring directly, to and fro, the migrations of the 
latter, so far as understood distinctly pointing to that con- 
clusion. 
