Common eider (Somateria mollissima borealis)

Closeup of a female common eider on her nest.
Photo: Stein Ø. Nilsen / Norwegian Polar Institute

The common eider is monitored due to that it is a significantly important species in the Arctic marine food chain. Eiders feed on benthic organisms and can therefore be an indicator for this part of the ecosystem. Significant declines in the population sizes of the four eider species (steller's eider, king eider, common eider and spectacled eider) have been recorded in many Arctic areas. On the mainland, common eider has the Red List Near Threatened (NT) status, while the Svalbard population has the Least Concern (LC) status. In the Kongsfjord in Svalbard, since 2012 a 27% decline in the nesting population has been recorded.

What is being monitored?

Breeding population of Common eiders in Kongsfjorden

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The number of breeding eiders on the islands in Kongsfjorden varies between years. Previously, the breeding population of eider has been determined by the ice situation in the Kongsfjord. In recent years there has been no ice on the Kongsfjord, and there are probably other factors affecting the eider population. In the period from 1981 until 1997, population of eider females in the Kongsfjord ranged between 3000-4000 individuals. From 2000 to 2012, the population varied between 2,500-3,500 individuals. The recent years show a negative trend in the eider population in the Kongsfjord. Today’s breeding population (2017) of eider in the Kongsfjord is 2,561 individuals.

Status and trend

The present population of common eiders is estimated to be between 13,500 and 27,500 pairs.

Even without reliable population numbers from historical times, it is assumed that uncontrolled harvesting of eggs and down at the beginning of the 20th century affected the population negatively.

The harvesting resembled plundering, affecting the breeding success negatively. This and other potential anthropogenic factors contributed to the decision to give the species total protection in Svalbard in 1963. Further 15 bird sanctuaries were, furthermore, established in 1973, to secure important nesting areas for birds, especially common eiders and geese. Because of the special protection given to the species it is important to monitor it over time, and understand what affects it.

The population of common eiders in Kongsfjorden, including the Kongsfjorden and Blomstrandhalvøya bird sanctuaries, has been monitored by the Norwegian Polar Institute since 1981.

Common eider population development can be affected by climate. In the Arctic, the climate is changing rapidly, with both higher temperatures and lessice and snow cover. This may affect the physical conditions for breeding, including the timing of snow and ice melt on the islands and changes in the marine environment affecting the availability of prey.

Causal factors

The climate has changed in the last 10–15 years of the monitoring period in Kongsfjorden. This includes higher air and ocean temperatures, a decrease in sea ice and earlier snow and ice melt in the spring (Vihtakari et al. 2018).

In the Arctic, the climate is rapidly changing, with increases in air and sea temperatures as well as reduced ice and snow cover. This can affect the physical conditions for nesting. The time period when the islets are free of ice and snow changes, and the eider can start breeding earlier. The sea temperature is higher, which can affect food availability for eider. In recent years, the Kongsfjord has also received more and more visits from polar bears who come to the islets in the summer (Prop et al. 2015). The polar bears eat eggs, however most likely this does not affect the breeding population in the fjord.

In the 1980s and 90s the breeding population of eider were highest in years with little ice in the Kongsfjord. Both in 2013 and in 2016 we had a low number of eiders that nested in the Kongsfjord (1941 and 1901 nesting eider respectively). From 2012 to 2017 the breeding population of eider females in the Kongsfjord has been reduced by 27%. This change cannot be explained by the ice situation, as the Kongsfjord has been ice-free during the breeding season since 1999. Studies of the eider females’ migration, using light loggers, show that two-thirds of the eider females from the Kongsfjord overwinter in Iceland, while approximately one-third overwinter on the coast of northern Norway (Hanssen et al. 2016). Studies carried out show that eider females overwintering in Iceland are affected by climate conditions in the winter area (measured using the North Atlantic Oscillation (NAO index) (Guery et al. 2017). Changes in the ocean temperature in this area probably affect the access to food sources in the winter area, such as reduced food availability or access to food of lower quality. For eider females overwintering in Iceland, this may result in their dying in the winter area as a result of poor access to nutrition/food, or that they arrive at the breeding area on Svalbard in poor condition and that they therefore will not nest.

Consequences

The eider population in the Kongsfjord has shown a downward trend since 2012. In the coming years, it is important to clarify the causes of this decline. A consequence of the downward trend will be a reduced grazing of the eider’s food organisms.

About the monitoring

Previously, the breeding population of eider has been determined by the ice situation in the Kongsfjord. In recent years there has been no ice on the Kongsfjord, and there are probably other factors affecting the eider population. Future studies will be able to provide information about this. Is it the overwintering area that has become worse for eider females in the Kongsfjord?

Eiders are monitored as the species might be a good indicator to study the effects of climate change in the Arctic.

The Arctic Council working group Conservation of Arctic Flora and Fauna (CAFF) has selected the eider species as one of several groups of Arctic birds that should be monitored. To restore, stabilize and manage the eider populations in a sustainable manner, CAFF has prepared circumpolar monitoring and action plans for these species. It is a national responsibility to follow up this work in Svalbard.

Places and areas

Relations to other monitoring

Monitoring programme
International environmental agreements
Voluntary international cooperation
Related monitoring