Náttúrufræðingurinn - 1954, Blaðsíða 29

ISLENZKIR FUGLAR VIII
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often scantily lined with a few withered grasses and moss. As a rule the clutch
consists of 2 eggs, but occasionally of only 1 egg. Clutches of 3 or more eggs
have never been recorded for Iceland.
In Iceland the arctic skua is strictly migratory, and not a single record of its
octurrence in winter is known. Its arrival in spring takes place in the period be-
tween the iniddle of April and the middle of May, but most frequently it arrives
at the end of April or in the beginning of May. The exodus in autumn takes
place mostly in the latter half of August, but some birds may probably leave
earlier or in the first half of August or even at the end of July. In the first
week of September arctic skuas may still be present in some numbers, but after
that it disappears almost completely, and after the middle of September it has
never been observed in Iceland. Nothing is known about the winter quarters of
the arctic skuas of Iceland. Only very few have been ringed and only one bird
has been recovered abroad. This bird was ringed as young and it was shot in August
of the following year at Newfoundland.
The food and the feeding habits of the arctic skua are very varied, and they
also vary considerably with the locality. As evei-ywhere within its range it pursues
other sea birds and forces them to drop their prey or to disgorge. Its chief vic-
tims in Iceland are the arctic tem, the kittiwake, the puffin, and the fulmar. It
should be mentioned, however, that only in the Eyjafjöll and Mýrdalur districts
in S. Iceland is the arctic skua known to attack the fulmar, but in these very di-
stricts there are many large inland colonies of the fulmar. The arctic skua also
takes eggs and young of many species of birds and kills adult birds such as passe-
rines and small waders. It also feeds on spiders, insects and insect larvae (especial-
ly the larvae of Charaeas graminis) as well as on carcass and fish offal. It is also
known to feed on berries of Empetrum and Vaccinium.
According to II. N. Southern, who has published data on the relative frequency
of the two colour phases of the arctic skua in Iceland (Ibis, 1943, p. 443), the
percentage of pale birds in SE. Iceland is only 10%, in SW. Iceland 20—30%,
and in N.Iceland 40%. Recent counts yielded somewhat lower figures for SW. Ice-
land (20%) and N. Iceland (30%), but otherwise they corroborate Southern’s
findings in all the main points.