Birds Taken by Surprise by Arctic Conditions in the Wadden Sea

© G. Reichert/ NPV Niedersächsisches WattenmeerWilhelmshaven,
16 February 2012
- Arctic weather conditions over
the last two weeks led to an almost completely frozen Wadden
Sea, which may have severe effects on wintering waterbirds
staying during this cold spell, as experts of the joint
Dutch/ German/ Danish group monitoring migratory birds (JMMB)
expect. Waterbirds suffer from bad food availability in
combination with the very cold temperatures, which some
will not survive. However, most birds managed to escape
quickly after the cold spell started further southwest to
West-European coasts to reach milder weather conditions.

In contrast to the previous years this winter started very
mildly and without frost. Due to that fact large numbers
of waterbirds like Barnacle Geese, Shelducks, Wigeons, Oystercatchers,
Grey Plovers, Red Knots, Dunlins, Curlews and even Golden
Plovers and Lapwings remained in the Wadden Sea and tried
to overwinter. In addition, the recent storms pushed an
unusually large number of Kittiwakes and Little Gulls to
the Wadden Sea coast and some individuals of the very rare
gulls such as Glaucous and Iceland Gulls were observed.

This winter’s late sudden severe cold caught the
birds by surprise. The cold spell started on 26th January
and within a few days the entire Wadden Sea from Denmark
to the Netherlands was frozen. All higher tidal flats are
covered now by a thick layer of ice and many birds concentrate
on temporarily ice-free lower tidal mudflats, where they
can feed. This caused the escape of the most birds from
the Wadden Sea. Especially Geese and Wigeons, the vegetarians,
flew to milder regions as well as shorebirds, whose numbers
dropped rapidly. Thousands of Dark-bellied Brent Geese arrived
in the northern Wadden Sea in late January, but on arrival
the low temperatures, ice and snow cover forced them to
fly back within a few days.

These extreme temperatures pose a danger for the birds.
After the coldest night from 6th to 7th February with temperatures
below minus 15°C more than 90 dead shorebirds were found
by volunteers of the “Schutzstation Wattenmeer”
at the coast of Schleswig-Holstein, among them 70 Oystercatchers.
This shows that quite a number of birds did not find enough
food and did not have any fat reserves left and, therefore,
froze to death. Normally, birds with good body conditions
and fat reserves should survive minus 15°C easily as
well as arctic periods of several weeks.

If the cold spell continues, it is expected that more winter
mortality among birds may occur. Especially for Oystercatcher
this would be another negative impact on its population
level, which dropped by almost 50% over the last 20 years.
This species has suffered limited food stocks in large parts
of the Wadden Sea as a result of shellfish fisheries in
the Dutch Wadden Sea. Moreover, breeding success was very
poor in the past years, as revealed by the new Trilateral
Monitoring and Assessment Program on breeding success.

More information can be accessed at the Wadden
Sea - World Heritage
website

Last updated on 16 June 2014

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