Náttúrufræðingurinn - 1954, Síða 28

20
NÁTTtJRUFRÆÐINGURINN
bæri rækilega, og hefur hann meðal annars aflað gagna um fjölda-
hlutfall litarafbrigðanna hér á 'landi. Samkvæmt niðurstöðum hans
(Ibis 1943, bls. 443) er hlutfallstala skjóttra kjóa á SA-landi aðeins
10%, á SV-landi 20—30% og á N-landi 40%■ Síðari talningar hafa
staðfest þessar niðurstöður í aðalatriðum. Þó benda þær til þess, að
hlutfallstölurnar fyrir SV-land og N-land séu fullháar hjá Southern.
Mun réttara að telja hlutfallstölu skjóttra kjóa á SV-andi 20% og
á N-landi 30%. Annars væri mjög æskilegt, að fjöldahlutfall litar-
afbrigðanna í hinum ýmsu landshlutum hér á landi væri rannasakað
rækilegar, og er hér tilvalið verkefni fyrir áhugamenn um fuglafræði.
SUMMARY:
Icelandic Birds VIII. The Arctic Skua (Stercorarius parasi'ticus (L.)).
The arctic skua is a common breeding bird throughout Iceland. The greatest
breeding density is found in the lowlands, but it is nevertheless a fairly common
breeding bird at higher levels, or up to the 700 m. contour line. It nests in many
of the oases in the Central Highlands, in some places even right up to the margin
of the interior ice-caps. A nest has also been found in the nunatak mountains Esju-
fjöll within the 8.800 sq. km. ice sheet of Vatnajökull, and another nest was found
on a median moraine on the outlet glacier Breidamerkurjökull. The arctic skua
is also found nesting on certain coastal islands. In the Breidafjördur archipelago
it is thus not an uncommon breeding bird.
In the breeding season the arctic skua occupies a wide range of habitats. In
many districts it nests mainly or almost exclusively on moorlands or marshes,
either within wide expanses of continuous moorlands or in small marshy depres-
sions. In such areas it shows a preference for swampy places, although the nest
itself is always situated in a fairly dry spot. In other parts of the country, where
moorlands are scarce, the arctic skua may occupy quite different habitats. There
it may be found breeding on heathy ground, in lava streams or on sandy or gra-
velly coastal plains. Thus it is probably more common on the vast fluvio-glacial
outwash plains (sandar) in SE. and S. Iceland than anywhere else in the country.
There it often nests in scattered loosely knit colonies. Similar breeding concentra-
tions of arctic skuas are also to be found on Héradssandur in NE. Iceland, as well
as on sandy flats at the bottom of some of the fjords and bays of the north coast.
But the arqtic skua is by no means a colonial breeder everywhere in Iceland. In
many districts, especially in its moorland habitats, it nests almost invariably singly.
When nesting in lava flows or on sandy or gravelly flats the arctic skua shows
a preference for places with some vegetation. Lava flows overgrown with moss,
and gravelly flats with thin and patchy moss carpets are thus favoured. And in
drift-sand areas it mainly nests in patches of lyme-grass (Elymus arenarius) or
on lyme-grass dunes.
The eggs are laid at the end of May or in the beginning of June. The earliest
recorded date for a complete clutch is May 23. The nest is merely a depression
in the ground (diameter 18—21, depth 3—5 cm.), sometimes unlined, hut more