Náttúrufræðingurinn - 1969, Side 46

40
NÁT T Ú R U F RÆ ÐINGURJNN
lightbrown glass with a large number of gasbubbles and sparse crystals of
plagioclase and olivine. Large areas composed of metamorphic rocks are to
be found in Scotland, Hebrides, North and Northwest Ireland, Shetland Is-
lands, Scandinavia and Greenland. On Iceland metamorphic rocks of tliis kind
have never been found, since Iceland is geologically a very young country.
In tlie table the minerals quarz, plagioclase and alkali-feldspar are the most
conspicuous constituents, but ihese are tlie principal rock forming minerals
of granite and gneiss. Tlie alkali-feldspar is mostly a microcline which is
characteristic of metamorphic rocks. One of the birds carried garnet, but this
mineral is connnon on the metamorphic rocks of the Scottish Highlands and
Northwestern Ireland.
The records indicate that of the 14 species of birds caught on the island
only snow buntings of a nominate race were seed carriers. That tlie seeds
were in the gizzard and none in the stomach indicates that thc birds had
not been caught feeding but apparently consumed the seeds at an earlier
time. The accompanying rocks and minerals definitely show that tlie birds
liad not been on the mainland of Iceland, i.e., there was no old Icelandic
basalt in the gizzards. On the olher hand, there were grains of cinder jticked
up in Surtsey and mostly metamorphic rocktypes and younger sediments which
must have been collected by the birds outside Iceland.
Most of the seed identified from the gizzards are of species rather common
both to Iceland and the British Isles, such as Empetrum, Scirpus, Spergula
and Carex fusca, Polygomnn persicaria, however, can be regarded as a Euro-
pean species, which only survives in Iceland around cultivated areas and
hotsprings.
One seecl was identified as Andromeda polifolia L. This plant is definitely
not found growing in Iceland, but is native to Greenland as well as the
British Isles, where it is found in bogs fronr Somerset to tlie Ilebrides. A few
seeds are with hestitation identified as those of Medicago sativa. If this was
correct it would almost eliminate both Greenland and Iceland frorn being
the place of origin of the seeds. It is concluded that the Seed in the gizzards
of the snow buntings were together with the mineral grit either picked up
by thc birds in the British Isles and carried l>y them over the ocean to
Surtsey on thcir migration to Greenland via Iceland, or picked up in Surtsey
witli tlie Surtsey ash. Should the former statement be true, it would prove
that birds transport seed over long distances and that some seeds at least
still retained their germination ability. Should the latter statement be accepted
it would indicate that seed of Carex and Polygonum could drift to Surtsey
and retain their germination ability.