Research on common scoters
The common scoter (Melanitta nigra) is ironically one of the rarest ducks to breed in Iceland. They are found mainly on Lake Mývatn and other similar wetland areas in Northern Iceland, more specifically in Þingeyjarsýsla District.
Common scoters – two drakes and a duck. Lake Mývatn, 27.05.2006. Photograph: Daníel Bergmann.
The common scoter's numbers are not in decline, but its breeding population is small – only around 300 breeding pairs (Ævar Petersen 1998) – and the bird is therefore on the Icelandic Red List. The Mývatn Research Station has monitored the common scoter population at Lake Mývatn since 1974. Little research on common scoters has taken place elsewhere in Iceland, however, and studies at Mývatn focused on the part that common scoters (and other waterfowl) play in the Mývatn biosystem (e.g., Arnþór Garðarsson 1991, 2006; Arnþór Garðarsson & Árni Einarsson 1994, 2004), their behaviour (Bengtson 1966, Ólafur K. Nielsen 1998) and their life expectancy (Fox, Petersen & Frederiksen 2003).
In the summer of 2009, a team of researchers embarked on a study of common scoters at Sandur and Sílalækur, two wetland areas in the Aðaldalur Valley in Northern Iceland. The Sandur and Sílalækur wetlands have now been shown to be home to close to 20% of Iceland's common scoter population.
The Aðaldalur study focuses mainly on the migratory patterns and wintering grounds of Icelandic common scoters, of which little is known. Few Icelandic scoters marked with traditional bird rings have been recovered. Earlier recoveries suggested that Icelandic scoters spend the winter in an area that stretches from the south of England to Portugal (Ævar Petersen 1998). Researchers at Aðaldalur hope to obtain more precise data on the migratory patterns and behaviour of these elusive birds.
For the Aðaldalur study, so-called geolocators – little devices that track the changes in light levels – were fitted on the legs of common scoters in the summer of 2009. Geolocators are designed to be light – ours weigh a mere 1.8 grams – and therefore store data rather than transmitting it by means of satellite or radio. For this reason, a bird carrying a geolocator must be recaptured in order to download data on its travels. Birds must thus return to the same breeding grounds year after year, which appears to be the case with scoters. It also helps if birds are long-lived.
A geolocator fitted on a common scoter. The geolocator is attached to a coloured ring that is then placed on the bird's leg. Aðaldalur, 15.06.2009. Photograh: Geoff Hilton.
Geolocators were placed on a total of 13 common scoters in the summer of 2009, nine of which birds were successfully recovered the following year. Eight of the marked birds were caught live at their nests and one was found dead in a fish net. Of the eight live birds, one had lost the geolocator that it had been spotted on its leg only days before.
Data from the remaining eight geolocators shows that the Icelandic birds spent the winter in various coastal areas ranging from NW-Ireland, the west and east coasts of Scotland, the west coast of Wales, the south coast of England and the coasts of Spain and Portugal. Many of the birds spent the winter farther north than earlier data had suggested – the reason for this may be the limited nature of earlier data, or it may be that common scoters remain farther north than they once did. The latter explanation would be in keeping with what one might expect in terms of global climate change – most recoveries of marked common scoters are by now some years old. The graph below shows a rough graphical representation of data for one of the scoters in this study, which demonstrates that the bird spent the winter in the vicinity of NW-Ireland.
One of the most interesting findings was that birds from the same breeding area in Iceland scatter to many different wintering grounds. This is quite prudent from an evolutionary perspective, as it means that a major disaster or mishap in winter will not wipe out the entire population at the same time. The 2002 Prestige oil spill, for example, occurred at a location off the coast of Spain where common scoters from Iceland often spend the winter, and many common scoters presumably died in the spill. This is not, of course, to say that oil spills steer the evolution of common scoters, but various natural events can also occur that affect a bird's likelihood of survival.
Conservationists in the UK have observed and taken part in our research with great interest. Common scoters are relatively common as winter guests to the UK but breed there only on very rare occasion. Little has been known about where these birds come from and return to, but it has been presumed that they flock to the UK from all of the species' various breeding grounds. Common scoters and their migration behaviour have been the subject of particular interest in recent years, as the birds keep largely to wintering grounds that are now being examined as potential sites for wind farms.
The Aðaldalur study is a cooperative effort involving three institutes: the National Environmental Research Institute (NERI) in Denmark, the British Antarctic Survey (BAS) and the Icelandic Institute of Natural History. Wildfowl and Wetlands Trust (WWT) staff members have also participated in the study.
The organisers of the research project wish to thank field assistants Geoff Hilton, Anne Harrison, Hannah Robson, Peter Cranswick and Jim Williams for their invaluable help. We would also like to express our gratitude to the landowners at Sandur and Sílalækur, in particular Gunnar Óli Hákonarson and Vilhjálmur Jónasson, for their assistance, goodwill and support for the project. Thanks also to the Wildfowl and Wetlands Trust for their financial support in purchasing geolocators. Finally, thanks to Daníel Bergmann and Geoff Hilton for their permission to use the pictures that appear on this page.
Arnþór Garðarsson 1991. Fuglalíf við Mývatn og Laxá. In: Arnþór Garðarsson & Árni Einarsson (eds.). Náttúra Mývatns (pp. 279-319). Hið ísl. Náttúrufræðifélag, Reykjavík. 372 pp.
Arnþór Garðarsson 2006. Temporal processes and duck populations: examples from Mývatn. Hydrobiologia 567(1): 89-100.
Arnþór Garðarsson & Árni Einarsson 1994. Responses of breeding duck populations to changes in food supply. Hydrobiologia 279/280: 15-27.
Arnþór Garðarsson & Árni Einarsson 2004. Resource limitation of diving ducks at Mývatn: Food limits production. Aquatic Ecol. 38: 285-295.
Bengtson, S.-A. 1966. Observationer rörande sjöorrens (Melanitta nigra) sexuella beteende på häckplatsen med speciellt avseende på lekgruppsbeteende. Vår Fågelvärld 25(3): 202-226.
Fox, A.D., Ævar Petersen & M. Frederiksen 2003. Recapture and survival rates of breeding female Common Scoter at Mývatn, Iceland, 1927-1958. Ibis 145 (2): 346 (abstract) + E94-E96 (online).
Ólafur K. Nielsen 1998. Atferli kafandarunga við fæðuleit í Mývatni. Náttúrurannsóknastöð við Mývatn. Fjölrit nr. 2. 35 pp.
Ævar Petersen 1998. Íslenskir fuglar. Vaka-Helgafell, Reykjavík. 312 pp.
Ib Krag Petersen, National Environmental Research Institute, Aarhus Universitet, Denmark
Ævar Petersen, Icelandic Institute of Natural History