Significance of the White Sea as a stopover for Bewick's Swans Cygnus columbianus bewickii in spring

Ibis - Tập 143 Số 1 - Trang 63-71 - 2001
Bart A. Nolet1, VALERY A. ANDREEV2, Preben Clausen3, Martin Poot4, ERIK G. J. WESSEL1
1Netherlands Institute of Ecology, Centre for Limnology, Postbox 1299, NL-3600 BG Maarssen, The Netherlands
2Committee of Environment Protection and Natural Resources of Arkhangelsk Region, Troitsky Avenue 49, Arkhangelsk, Russia
3National Environmental Research Institute, Department of Coastal Zone Ecology, Grenåvej 12, DK-8410 Rønde, Denmark
4Zoological Laboratory, University of Groningen, Postbox 14, NL-9750 AA Haren, The Netherlands

Tóm tắt

We searched for a major stopover site of Bewick's Swans Cygnus columbianus bewickii in the White Sea following the suggestion that one should exist on the stretch between Estonia and the breeding grounds (1750 km). We discovered 733 Swans in Dvina Bay during a late aerial survey in spring 1993. Subsequently, ground‐based research was carried out in May 1994, 1995 and 1996 in the Dry Sea, a tidal, shallow bay with fresh to brackish water just north of the Dvina Delta. The total number of passing Bewick's Swans was estimated at 10974 (1994), 9593 (1995) and 17 972 (1996) (32–60% of the flyway population). Estimated peak numbers staging were 1500–2000 (9 May 1994), 4937 (17 May 1995) and 4457 (24 May 1996) (> 5–16% of the flyway population). The Swans foraged almost exclusively on submerged water plants apart from some supplemental feeding on emerged food plants around high tide. Stoneworts Chara spp. were an important food in the late spring of 1996, because they grew in places where bog streams quickly melted the ice. At this latitude (65d̀N) food alternatives to the submerged macrophytes are rare in spring, but we cannot rule out the possibility that the Swans forage on grass rhizomes on inundated pastures. One bird tracked by satellite staged 15 days in Dvina Bay, of which four days were spent in the Dry Sea, in accordance with other indications that the Dry Sea is part of a larger stopover site within Dvina Bay. Recent evidence shows that the Swans largely skip the White Sea during autumn migration. However, in spring the birds probably need this stopover to be able to carry reserves to the breeding grounds. At present, the preservation of the submerged vegetation in Dvina Bay seems to be crucial to the conservation of this Bewick's Swan population.

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Tài liệu tham khảo

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Ibis

Tập 143 Số 1

63-71

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