Náttúrufræðingurinn - 1976, Blaðsíða 107

the last third of March they become num-
erous on the Breidamerkursandur breecl-
ing grounds, provided that the weather
conditions are favourable; in cold years
their peak arrival may be delayed until
the first third of April or even later. In
autumn they start deserting the nesting
grounds in mid-September or even ear-
lier, the latest usually disappearing Octo-
ber 10—20. In recent years the Gr. Skua
population has increased: In a 1000 m2
area at Kvísker wliere I counted 40 breed-
ing pairs in 1951 there were 170 pairs in
1971. This increase has taken ]>lace de-
spite unusually heavy mortality of young
from 1957 to 1965. In sonte years during
this period hardly any young ffedged.
Even half-grown young were found dead
without marked signs of emaciation. The
cause of this unusual mortality is un-
known.
Arctic Skuas breed commonly, oft-
en semi-colonially, in the lowlands and
to some extent in the foothills. In spring
this species starts to arrive April 18—28,
but it mainly arrives in early May and
most liave arrived by May 10. In autumn
the last birds usually disappear in the
first half of September. Out of 200 nest-
ing birds in 1948 only 10% belonged to
the pale phase and 90% to the dark
phase. The third colour phase, which is
much rarer, has a white patch on thc
front edge of the wing and anolher one
on the belly. It is seen almost annually
on tlie Breidamerkursandur.
The Great Black-backed Gull is
a common breeding bird. It shares the
l'luvio-glacial outwash plains with the
Great and Arctic Skuas, but it also nests
on the top of Ingólfshöfdi (200—300
pairs) and even on median moraines near
the front of the glaciers. It occasionally
starts laying in mid-April but in most
years not until the end of April or the
lirst week of May. Great Blackbacks are
cbiefly resident birds; they are fairly
common at sea in winter although less
so in November—January. The Lesser
Black-backed Gull was first observ-
ed in small numbers in the years 1930—
1940. Since 1940 it has gradually increas-
ed in numbers. The first nest was found
in 1937 at Gljúfursá near Fagurhólsmýri.
Ltiter, small colonies were formed else-
where, but contrary to the skuas and the
Great Blackback, the Lesser Blackback
does not nest on the outwash plains but
on upland heaths near river gorges in
tlie foothills, on ntoraine hillocks, and
like the Great Blackback even on median
moraines near the front of glaciers. In
1956—1966 20—30 pairs nested on Ingólfs-
höfdi but this colony has since then
dwindled to 1—2 pairs. The Lesser Black-
back is strictly migratory, arriving in mid-
April and laying in early June. The
Herring Gull was first seen in 1946
and later on several occasions, mostly at
sea. Since 1955 Herring Gulls have been
observecl annually, in summer frequently
in small nuntbers on hayfields together
with Lessar Blackbacks, and in winter at
sea. In 1956 three pairs with small young
were found on Ingólfshöfdi and since
then 2—4 pairs have nested there annu-
ally. In 1958—1968 1—2 pairs nested on
the median moraine on the Breidamerk-
urjökull and in 1972 six pairs nested
there. In 1966 8 pairs nested at Kvíár-
jökull among Lesser Bleckbacks, but next
year they had disappeared.
The Common Gull was first seen
at Kvísker in 1937 (2 birds) and since
then on various occasions (1951, 1963,
1964, 1966, 1972 and 1973), but mostly
only single birds. The Glaucous Gu 11
is fairly comnton at sea in winter, from
October onwards. However, their numb-
ers increase greatly from February on-
wards, when the Capelin (Mallotus vil-
losus) moves into inshore waters to
spawn. Peak numbers (many thousands)
are reached in Marcli and early Aptil;
from then on their numbers fall sharplv
although some immature birds may stay
until May. One pair is said to have bred
on the top of Ingólfshöfdi sometime dur-
ing the years 1905—1912, but this is not
satisfactorily substantiated. The Ice'-
1 a n d G u 11 is fairly common at sea in
winter although far less common than the
Glaucous Gull and less littoral in its
liabits. The Black-lieaded Gull was