Náttúrufræðingurinn - 1954, Page 25

ÍSLENZKIR FUGLAR IX
133
in such places there is, however, always a considerable distance between the nests
and each pair niaintains a well marked territory.
East of Skeidarársandur is Breidamerkursandur, a 30 km long but compara-
tively narrow strip of land between the Breidamerkur glacier and the sea, which
is occupied by about 1500 pairs of great skuas. These two sandar areas, which are
separated by the small, but closely settled farming district of öræfi, are the most
important breeding stations of the great skua in Iceland. On the south coast, west
of Skeidarársandur, the great skua also breeds in considerable numbers, especially
in the Kúdafljót delta and on Mýrdalssandur, south-east of the icecap of Mýrdals-
jökull, where about 500 pairs are supposed to breed. According to our present
knowledge the total number of breedig pairs in all the remaining colonies of the
great skua in Iceland (cf. fig. 1) certainly does not exceed 1000.
My recent investigations into the distribution and numbers of the great skua
in Iceland, which form the basis of the above information, have thus revealed
that the total number of breeding pairs in Iceland must be about 6000. This fi-
gure is of course largely based on estimates, but I do not think it likely that it
will be shown to differ greatly from the actual number of breeding pairs. In this
connection I would like to point out, that I have, myself, visited many of the
great skua colonies, ■ and that I have recveived valuable information about others
fvom local obsei’vers.
The only known breeding stations of the North Atlantic great skua outside
Iceland are in the Shetlands, Orkneys and Faeroes. The number of breeding pairs
in the Shetlands and Orkneys is said to be 1000, and in the Faeroes 200. The world
total of breeding pairs would thus be 7200. The above figures show that the North
Atlantic great skua must be one of the rarer sea birds of the North Atlantic,
and that Iceland, with no less than 83% of the world population, is its distri-
bution centre.
The great skua is a large and conspicuous bird and is famous for its aggressive-
ness on the breeding-grounds. Thanks to these attributes, and to its small num-
bers, restricted distribution, and social nesting habits, it would not be very diffi-
cult to make a fairly accurate census of all occupied nests or breeding pairs within
its North Atlantic range in the same season. The North Atlantic great skua might
thus tum out to be a very suitable object for studies in population dynamics and
population trends, and for studies of the factors controlling them.
Although the great skua is mainly confined to low-lying flats near the coast
it may be found breeding 20—30 km inland and up to 100 m above sea level
in the northernmost part of Skeidarársandur and in the Markarfljót delta valley.
The great skua shares the sandar habitat with the arctic skua and the great black-
backed gull. Although these 3 species may occupy the same area they do not
usually mix but keep more or less apart. This is doubtless a result of the hostile
attitude prevailing between them. On the whole it seems rather surprising that
three such bold and aggressive predators and pirates can manage to live side by
side. The extent of vegetation in the sandar areas occupied by the great skua varies
considerably. Quite extensive areas may be practically bare of vegetation, while
in other areas the surface of the sandur niay be overgrown with short grass,
especially in moist places, or covered with a thin moss carpet. In drift-sand areas
the lyme grass (Elymus arenarius) may have a wide although patc.hy distribution.