Náttúrufræðingurinn - 1980, Síða 150

HEIMILDIR
Bjömsson, Hálfdán 1976. Fuglalíf í Öræfum,
A.-Skaft. Náttúrufræðingurinn 46: 56—
104.
Jómsson, Hallgrímur 1946. Skagafjörður. Ár-
bók Ferðafélags Islands 1946.
Southern, II. N. & E. C. R. Reeve 1941.
Quantitative studies in the geographical
variation of birds — The Common
Guillemot (Uria aalge Pont.). Proc. Zool.
Soc., Ser. A, 111:255 — 276.
Southem, H. N. 1951. Change in status of the
Bridled Guillemot after ten years. Proc.
Zool. Soc. Lond., Ser. A, 121: 657 — 671.
Tuck, L. M. 1961. The Murres. Ottawa.
S U M M A R Y
Numbers of Bríinnich’s (Uria
Lomvia) and Common
Guillemots (Uria aalge) at
Icelandic breeding stations
by Thorstemn Einarsson,
Laugarásvegur 47, 104 Reykjavík, Iceland.
Visits were made to 19 Icelandic breeding
stations, during 1938—1978. Counts and
estimates were made, mainly 10. June—20.
July, for obtaining the proportions and
numbers of the two species, and the propor-
tion of Bridled Guillemots within the Com-
mon Guillcmot populations.
For estimating numbers I have tried to
divide the cliffs into parts, and classify the
different types of ledges. Counts were made
at many ledges where birds were linearly
distributed, to get numbers of birds per
metre, multiplying by the total length of
ledges. Where birds formed groups, on
stacks and broad ledges, numbers were es-
timated visually, or from numbers of eggs
which were collected from these sites.
It is clear that these estimates are crude,
and they are carried out over an extended
period of time. Sometimes it has been pos-
sible to compare counts of birds to numbers
of eggs taken. The results have shown that
numbers of eggs have been a third of the
numbers of birds.
The results (Fig. 1, Tables I and II) show
an increased proportion of Brúnnich’s Guil-
lemots towards the more northern colonies.
The proportion of Bridled Guillemots, how-
ever, declined towards the northern and
eastern parts.
By far the largest bird cliffs are Látra-
bjarg, Hælavíkurbjarg (not shown on Fig.
1), and Hornbjarg, all on the NW. penin-
sula. These combined hcld about 93% of all
the breeding pairs. Four more breeding
stations are known to me for which no es-
timates are available; Hólmsberg (Gull.),
Ritur (N.-lsaf.), Blæjan (S.-Þing.), and Ós-
fjöll (N.-Múl.).
A remarkable difference in zonation of
Brúnnich’s and Common Guillcmots on the
sea below bird cliffs, was noted during the
study. This was especially obvious at
Drangey, where snare-rafts were formerly
used for catching birds. The main species
cought on these rafts, which were placed
near the island, were Common Guillemots,
Puffins, and Razorbills. This is highly in-
teresting in light of the near complete
dominance of Brúnnich’s Guillemots nesting
on the island. This reflects the more off—
shore habits of Brúnnich’s Guillemots.
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