Náttúrufræðingurinn - 1952, Blaðsíða 28

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NÁTTÚRUFRÆÐINGURINN
not known to breed in the large north-western peninsula (Vestfirdir), nor in the ad-
joining area between Breidafjördur in the West and Hrútafjördur in the North. But
immediately to the east of the low liills on the eastern side of Hrútafjördur it is found
breeding and from there throughout the North and the North-East of Iceland as far
as Fljótsdalshérad it is in many places a fairly common breeding bird. It has not been
found breeding on the indented east-coast south of Héradsflói, except for an old iso-
lated case recorded at Djúpivogur in Berufjördur. No authenticated breeding records 4
are available from the district of Austur-Skaftafellssýsla in the South-East, but
nevertheless I do not think it is unlikely that it may breed there, tlie most probable
place being the parish of Mýrar to the west of Hornafjördur. Farther to the west it is
again found breeding in considerable numbers in Medalland in the district of Vestur-
Skaftafellssýsla, and from there throughout the South and the South-West as far as the
Snæfellsnes peninsula it has a wide distribution as a breeding bird.
In the breeding-season the Slavonian grebe frequents lakes, ponds and meres and
occasionally quiet reaches of slow-flowing rivers. It shows a marked preference for
waters with fairly rich vegetation and rich and varied animal life, and these habitat
preferences partly explain its peculiar distribution in Iceland. As a breeding bird it is
mainly restricted to the lowlands and valleys, being most common below the 100 m
contour line. Lake Mývatn (277 m above sea-level) is an exception to this rule. No-
where in Iceland is it found breeding higher or as high above sea-level and nowhere
is it as abundant as there. The number of breeding-pairs in this area is estimated to
amount to a few hundreds.
The nest is composed of wet decaying water-weeds and is usually floating on the
water among growing vegetation of Carex rostrata, Equisetum fluviatile, Scirpus pa-
lustris or Menyanthes trifoliata. Nests may also be built on beds of submerged water-
weeds, sudr as Myriophyllum spicatum, and on Lake Mývatn branches of willow (Salix
phylicifolia) or birch (Bctula pubescens) reaching into the water often serve as
anchorage for the nest. In some cases the nest is built up from the bottom of shallow
water with no cover at all. In other cases nests may even be found on relatively dry
banks of lakes or on sandy or gravelly shores of lakes, but such nests are most likely
built at a time when the water-levcl is considerably higher. The clutch consists of 4—5
eggs, occasionally also of 3 or 6 eggs. The eggs are laid in June, in favourable seasons
in the first half of that month. But owing to the frequent destruction of nests and
eggs through storms or changes in water level clutches of fresh eggs are not rarely
found in July and even in August. On Lake Mývatn tlie Slavonian grebe either breeds
singly, each small bay or inlet in that case being occupied by one pair only, or in
small colonies.
In Iceland the Slavonian grebe is mainly migratory, arriving in spring in April, on
the average about the middle of that month, and leaving in autumn in late September
and October. At Lake Mývatn the exodus in autumn begins in the second half of
September and continues until the lake freezes over, which usually occurs some time in
October. In the neighbouring coastal regions (Húsavík) Slavonian grebes are observed
on the sea throughout October and the first week of November. And in Southwest-
Iceland odd birds are met with on coastal waters throughout the winter. A marked
bird has been recovered in the Faroes in November. Nothing, however, is known for
certain about the winter quarters of the species.
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