Náttúrufræðingurinn - 1954, Blaðsíða 27

ISLENZKIR FUGLAR IX
135
their fourth summer 2 were shot off N. Iceland (in May and early August).
A 5 year old bird and an 8 year old bird were shot on Breidamerkursandur where
they had been banded as chicks. Finally it may be mentioned that a great skua
banded as fledgeling in the Faeroes was recovered in its second summer off E. Ice-
land.
The recoveries of banded birds reveal that Icelandic great skuas leave Ice-
landic waters in winter and move southward, mainly to the SE. (coasts of We-
stern Europe) and to a less degree also to the SW. (Newfoundland Banks). This
is supported by the fact that there exist no winter records of the great skua in
lcelandic waters fiom the period November to January. The only exception is
a specimen in the Reykjavík Museum, which was shot on December 28 in Faxa
Bay, SW. Iceland. On the other hand the northward movement of the great skua
in spring seems to begin rather early. Thus I have observed great skuas in the
waters off the south coast of Iceland in the latter half of February. Recoveries
of banded birds indicate that the great skua does not reach sexual maturity until
it is 3—4 years old and most likely not until its fourth year. Immature birds
seem to migrate northward in spring like the adults. One-year-old birds may not
take part in this northward movement in spring to any extent but 2- and 3-year-
old birds certainly do so in increasing numbers with increasing age. These birds,
however, may spend the summer far away from the breeding-grounds, which is
demonstrated by the fact that immature Icelandic great skuas have been recovered
in summer off Newfoundland and SW. Greenland and that a 2-year-old Faeroe
bird has been recovered in summer off E. Iceland.
The great skua is very rarely seen on land except on the breeding-grounds. On
the other hand it may be observed during summer off all parts of the Icelandic
coast, usually only as single birds, although groups of 2—3 birds may occasionally
occur. The coastal waters off the SE. coast, where the large great skua colonies
are situated, form an exception to this rule. There 20—30 great skuas may often
be seen at the same time following in the wake of a ship.
The great skua, like the arctic skua, is known to pursue other sea birds and
to force them to drop their prey or to disgorge. The gannet and several species
of gulls have been recorded as its victims in Iceland. Compared with the arctic
skua the great skua, however, is decidedly a more pronounced predator than pi-
rate. The great skua also fishes for itself, but as it is not capable of diving, it
must be content with wliat it can snatch up from the surface. The indigestible
chitin jaws of cephalopodes have been found at great skua nest on Breidamerkur-
sandur, but they might well come from fish stomachs. Tlie great skua also takes
eggs and especially the young of other birds, and furthermore kills adult birds
in some quantity. The following species have been recorded as its prey in Ice-
land: Slavonian gi-ebe, fulmar, mallard, teal, wigeon, scaup, long-tailed duck,
eider, common scoter, red-breasted merganser. As yet the great skua is known
to prey upon adult fulmars in only one locality in Iceland. In July 1954 1 vi-
sited the isolated bluff of Hjörleifshöfdi rising from the Mýrdalssandur in S. Ice-
land. The crags of Hjörleifshöfdi are occupied by a laige fulmar colony, wliile
the surrounding plain is inhabited by great skuas. I was surprised to find a nar-
row zone of the plain round Hjörleifshöfdi littered with fulmar carcasses, the
number of which may have amounted to several hundreds. Only the great skua