Wilhelmshaven, 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