Common eider

Last updated 7 June 2024

The common eider (Somateria mollissima borealis) 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 Vulnerable (VU) status, while the Svalbard population has the Least Concern (LC) status. The eider population in Kongsfjorden has shown a downward trend since 2012.

Status and trend

The present population of common eiders is estimated to be between 13,500 and 27,500 pairs (Strøm & Descamps, 2013). The mapping of the breeding population of common eiders on Svalbard has so far only been conducted in selected areas (particularly on the west side of Svalbard). Climate change, with less ice on the east side of Svalbard in recent years, will make it possible to conduct a better survey of the breeding population of eiders in this area.

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

This and other potential anthropogenic factors contributed to the decision to give the species total protection in Svalbard in 1963. Furthermore, 15 bird reserves were established in 1973, with the aim of securing important breeding areas for birds, especially for common eiders and geese.

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

Causal factors

The climate in Kongsfjorden area has changed over the past 10–15 years. This includes higher air and sea temperatures, less sea ice, and earlier snow and ice melting 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 in the season. The sea temperature is higher, which can affect food availability for eider. In recent years, Kongsfjorden has also seen an increasing number of visits by polar bears coming to the islets in the summer (Prop et al. 2015).

In the 1980s and 90s the breeding population of eider were highest in years with little ice in Kongsfjorden. Both in 2013 and in 2016 we had a low number of eiders that nested in Kongsfjorden (1941 and 1901 nesting eider respectively). From 2012 to 2023, the breeding population of eider females in Kongsfjorden has been reduced from 3533 to 2325 individuals. This is a reduction of 34%. This change cannot be explained by the ice situation, as Kongsfjorden 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 Kongsfjorden 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 wintering area due to poor food availability or arriving at he breeding area in Svalbard in poor condition and that they therefore will not breed. Another reason for the decline of eiders in Kongsfjorden may be the increased predation from polar bears and polar gulls. The lack of good food conditions in northern Svalbard has resulted in many polar bears (with and without cubs) visiting Kongsfjorden to eat eggs from eiders and barnacle geese, among others. The glaucous gulls follow the polar bears in the fjord, and when the female eiders leave the nest, the eggs become accessible to both the polar bears and the glaucous gulls, contributing to the loss of many nests. In the years 2018, 2020, and 2022, more than 1000 nests were preyed upon by polar bears and glaucous gulls in Kongsfjorden. In the years 2019, 2021, and 2023, 100-150 nests were preyed upon by glaucous gulls. During these years, the polar bears arrived in Kongsfjorden after most of the eider ducklings had hatched. Favorable ice conditions in northern Svalbard, providing good feeding opportunities for the polar bears, were likely the reason for their late arrival in Kongsfjorden.

Consequences

The eider population in Kongsfjorden 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, especially on the west side og Svalbard, where most of the eiders are nesting.

About the monitoring

Previously, the breeding population of eider has been determined by the ice situation in Kongsfjorden. In recent years there has been no ice in Kongsfjorden, and there are probably other factors affecting the eider population. Future studies will be able to provide information about this. Is it the wintering area that has become worse for eider females or is it the increased predation that contributes to the decline of eiders in Kongsfjorden?

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.

Further reading