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Ib Krag Petersen

Mass mortality of adult Razorbills Alca torda in the Skagerrak and North Sea area, autumn 2007

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  • Martin Heubek, Aberdeen Institute of Coastal Science and Management, University of Aberdeen, c/o Sumburgh Head Lighthouse, Virkie, Shetland ZE3 9JN, UK;, Storbritannien
  • T. Aarvak, Norwegian Ornithological Society, Sandgata 30 B, NO-7012 Trondheim, Norway;, Norge
  • K. Isaksen, Agency for Urban Environment, City of Oslo, P.O. Box 1443 Vika, NO-0115 Oslo, Norway, Norge
  • A. Joensen, National Centre for Biosystematics, Natural History Museum, University of Oslo, P.O. Box 1172 Blindern, NO-0318 Oslo, Norway, Norge
  • Ib Krag Petersen
  • T. Anker-Nilssen, Norwegian Institute for Nature Research, P.O. Box 5685 Sluppen, NO-7485 Trondheim, Norway, Norge
An abnormal movement of auks occurred in the eastern Skagerrak in the third week
of September 2007. Large numbers of Razorbills Alca torda were reported along the
coasts of southeast Norway and western Sweden, many thousands entered
Oslofjorden (Norway), and their migration past the northern tip of Denmark into the
Kattegat began a month earlier than normal. This preceded heavy mortality of the
species that lasted several weeks, and numbered thousands of individuals. Unusually
for the time of year, Razorbills greatly outnumbered Common Guillemots Uria aalge
in reports of live and dead birds. Of 376 Razorbills collected in Oslofjorden, 87% were
adults, 9% immatures, and 4% juveniles. Among 326 adults, females (71%)
outnumbered males, and 18% showed two white inner bill grooves instead of the
normal one. All birds were extremely emaciated and had presumably starved to
death. Virtually all adults and older immatures were still regrowing their outer
primaries after the post-breeding moult, whereas those of juveniles were fully grown.
Most, if not all, belonged to A. t. islandica populations breeding in the British Isles,
Faroes or Iceland, and few, if any, were from A. t. torda populations of the Baltic,
Norway or Russia; the 23 ringed birds found in the Skagerrak and Kattegat, mostly
adults, all came from Scottish colonies. Population effects at these colonies were not
obvious, but adult survival in 2007–08 was low at one colony in eastern Scotland.
Long-term beached bird data indicated that while not on the scale of that in the
Skagerrak and Kattegat, Razorbill mortality was abnormally high over a wide area of
the North Sea in autumn 2007. The age and sex structure of the mortality and its
possible causes are discussed.
Sider (fra-til)11
Antal sider32
StatusUdgivet - 2011


  • Mass mortality Razorbill Skagerak North Sea

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