MYSTERIOUS KITTIWAKE MORTALITY IN N.NORWAY
The last few weeks the local newspapers have had notices about weak and
even dead gulls found on the outer coasts of our province, Troms, in
northern Norway. Initially there was the all too common confusion, and the
gulls were described as Common Gulls Larus canus, here indeed the most
common gull of villages and even towns, and an early migrant from wintering
areas around the North Sea. But afeter a few days it became clear that all
the dead gulls were instead Kittiwakes Rissa tridactyla, a pelagic species
also nesting in vast colonies on our outer coasts and islands. At the same
time, we heard from our correspondents that the Kittiwakes of the colonies
on the north and northwest coasts of Finnmark, the northernmost province of
Norway, had arrived as normal on the colonies this spring, but had
massively left the nesting areas again ca one week later and were now
nowhere to be seen.At the same time, dissection of a few dead birds showed
them to be severely undernourished, while at first sight there was no sign
of unduly many parasites, or toxins (tests are being conducted about these
aspects at the veterinary institute). One ringed dead kittiwake found here
in Troms turned out indeed to belong to one of the Finnmark colonies where
my colleague Rob Barrett, who has studied the Finnmark kittiwakes for many
years, has ringed large numbers of birds.
Indication this far are therefore that the Finnmark Kittiwakes have starved
after their return to the colonies (or maybe even already before that??),
that they have gradually weakened, to the extent that when they finally
decided to fly and find better pickings elsewhere, it was already too late
and they perished anyway, even though there are as yet few indications of a
dearth of food here in the troms area. In Finnmark, however, the annual
spawning of the Capelin Mallotus villosus, has been very meagre or even
absent many places, and it may well be that there is a connection there. As
we scientists are wont to say: further research is necessary! Capelins of
course are short-lived fish, most of whom spawn only once in their
lifetime---such a life strategy often leads to large oscillations in
numbers from year to year, just as we see in the grouse populations on
land; while heavy fishing pressure does not help much either.
Wim Vader, Tromsø Museum
9037 Tromsø, Norway
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