Náttúrufræðingurinn - 1957, Side 61

ÍSLENZKIR FUGLAR XIV
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ihe west there are also many large terneries. On the other hand it is interesting
to note, that on the Vestmannaeyjar (Westmann Islands) off the sonth coast only
odd terns are known to nest sporadically. Although the coast and coastal islands
constitute the distribution centre of the arctic tern in Iceland it also frequently
nests on lakes and rivers inland, even in suitable localities in the Central High-
lands. Thus a lew scattered pairs nest among the pink-footed geese (Anser
brachyrhynchus) in the large colony of this species in the Thjórsárver oasis at
the foot of the Hofsjökull icecap right in the centre of Iceland. On Lake Mý-
vatn tliere are several terneries on small islands in the lake and arctic terns
are known to breed or to liave bred in many other inland localities. A small
colony on an artificial island in the lake (Tjörnin) in the centre of Reykjavík is
apparently unique as Reykjavík has been claimed to be the only capital and
even the only town in the world with a ternery in the centre of the town. How-
cver, all the inland colonies of the arctic tern in Iceland are relatively small
compared witli the large coastal colonies.
Absence of closely related competing species and pressure of numbers are
probably the main reasons for the wide inland distribution of the arctic tern in
Iceland. This may also partly explain the wide range ol liabitats occupied in
the breeding season. Some of the more prevalent nesting-habitats in iceland
are dry littoral meadows (thrifts) witli low, dense vegetation, hummocky grass-
lands, marshes, sandy or gravelly flats with scanty vegetation, stony or rocky
ground, lava flows, shingle beaches and shingle banks in rivers, and occasionally
dried heaps ol sea-weed washed upon the shore. As an example of an unusual
nesting-site a small, woodecl island in a lake (Sandvatn) near Mývatn is worth
mentioning. On this island some arctic terns and black-headed gulls (Larus ridi-
bundus) nest on the „forest“-floor between good-sized birch-trees. However as a
rule the arctic tern avoids areas with luxuriant vegetation although it clearly
prefers sites with some vegetation to totally barren ones.
In Iceland the rnain laying-season of the arctic tern is the second and third
week in June. The date of its commencement may fluctuate considerably accor-
ding to the weather, and various other lacalized conditions may also affect the
time of laying directly or inderectly. Consequently there may be a considerable
difference in the commencement of laying from on colony to another even if
they are comparatively near each other. In some places laying may begin in late
May in good seasons while in other places laying may bc delayed until the
second half of June. Quite often considerable numbers of eggs are lost and be-
sides they are in many places c.ollected lor human consumption, causing the
birds to make replacements, sometimes even more than once, so that in many
colonies fresh eggs ntay be found along with young varying in age as late as
the encl of July.
Arctic terns rarely nest as close together as many other species of terns, and
llie colonies ntay therefore cover relatively large areas. The nest is merely a dc-
pression in the ground, sometimes lined with a l'ew withered grasses and moss,
or pebbles and pieces of broken shells, but just as often without any nest material
at a 11. Normally the clutch consists of 2 eggs, but frequently also of only 1 egg,
while clutches of 3 eggs are rare. 'l'here is frequently a heavy mortality among