Náttúrufræðingurinn - 1955, Blaðsíða 41

ÍSLENZKIR FUGLAR XI
33
following localities: the headland Tálkni between Patreksfjördur and Tólknafjördur
in the northwestern peninsula, Langanes in the northeast, the Westmann Islands
(Vestmannaeyjar) off the south coast, and Reykjanes in the southwest. As censuses
in the different colonies have not been made, the size of the Iceland population of
the glaucous gull is not known accurately. But on basis of all available informa-
tion the total number of pairs nesting in Iceland is estimated to be 3500.
The glaucous gull colonies in the Breidafjördur area are mostly on basaltic
mountain cliffs facing the sea. Usually these breeding cliffs are separated from the
sea by a narrow lowland strip —2 km in width, occasionally reaching 4 km. The
elevation of these coastal mountains varies from 200—600 m. Their lower parts
consist of steep screes or grassy slopes while the upper parts are precipitous cliffs.
The gull colonies occupy restricted areas on the cliff faces and these are very con-
spicuous, even from a distance, due to the luxuriant vegetation maintained by the
excrement of the birds. Within the colony the pairs usually nest singly although
on large ledges several pairs may nest together. The gulls nest preferably in the
upper parts of the cliffs and occasionally nests may be found on the very top. In
the gull colonies of Breidafjördur the glaucous gull was formerly the only nesting
bird, but now the fulmar (Fulmarus glacialis) has started to nest among the gulls
in most of the colonies. At Reykjanes and in the Westmann Islands the glaucous
gull is found nesting on isolated stacks and at one place in the Westmann Islands
it is found breeding on the sloping top of a high, rocky island (Hellisey). This
latter nesting place is quite unique as, in 1944, I found there four species of gulls
(Larus argentaíus, hyperboreus, marinus and fuscus) nesting together on the top
of the island while the cliffs were being occupied by a fifth species, the kittiwake
(Larus tridactylus).
The nest of the glaucous gull is very similar to that of the great black-back
(Larus marinus). It is mostly composed of moss and grass mixed with some feathers
from the birds themselves. The clutch consists of 2—3 eggs, apparently more often
3 in Iceland. The eggs are laid about the middle of May or shortly afterwards,
the laying season thus being slightly later than that of the great black-back. In
spring the glaucous gulls start visiting the nesting sites in April and are then often
seen soaring in flocks high in the air above the cliff-tops.
It is generally considered that the glaucous gull is a resident bird in Iceland,
and this is no doubt true. It is not unlikely, however, that small numbers of Ice-
land glaucous gulls may inove southward in winler, but tliere is no information
available about tliis, and such information can only be obtained tlirough ringing.
During the winter, the glaucous gull is common in inshore waters all íxiund the
coasts of Iceland, and occasionally it may be found on lakes and rivers some distance
from the sea. A large part of the winter population, however, is without doubt com-
posed of migrants from more northerly regions, as is indicated by two specimens
ringed as young in Spitsbergen and recovered in Iceland.
No systematic observations have been made on the food and the feeding habits
of Iceland glaucous gulls. The stomach contents of a few specimens investigated by
me consisted of molluscs (Mytilus edulis, Littorina palliata), crustaceans (Hyas),
echinoderms (sea-urchins), and fisli (Ammodytes). Although the food and feeding
liabits of tlie glaucous gull and the great black-back seem to be very similar, I have
3