© Daniel Bergmann
The Common Eider is the largest duck in the Northern Hemisphere. Large body size is advantageous for birds like Common Eider which rely on body reserves for incubation. The common eider sits on her eggs 99% of the time during the 25-26 of incubation and only leaves to drink. However, the common eiders eat before laying the eggs and whilst they are still laying eggs. One day passes between the laying of the eggs, and the development of the embryos halts until the female starts to incubate; therefore, all of the eggs hatch at the same time.
Most ducks in Iceland migrate from the temperate zone, with main wintering grounds in the British Isles and in Western Europe. Conversely, the Common Eider originally comes from the Arctic and is sedentary in Iceland. Nevertheless, the Common Eider has reached regions that are more southern, it breeds for example in the British Isles and in Scandinavia, and winters in Wadden Sea.
The Common Eider is divided into between five to seven sub-species. This is uncommon amongst ducks; normally, there is no geographical distinction between populations of the same species.
The Common Eider (and other eider ducks) uses the wings to swim below the surface, just like guillemots and penguins. Most other diving ducks (for example the Tufted Duck and the Greater Scaup) only use their legs.
Common Eiders lay fewer eggs than most other ducks (4-5 instead of 8-10), but the young are proportionately bigger (in relation to the size of an adult bird) than other ducklings. (The Harlequin duck represents an intermediate, laying 5-8 eggs). This is an adaptation to bringing up the ducklings on the sea as opposed to on freshwater.
© Daniel Bergmann
The common Eider often breeds in colonies on small coastal islands, whereas the other species typically nest solitarily in wet, tundra environments. Eiders frequently move between circumpolar countries from summer to winter, so effective conservation requires international cooperation.
The Conservation of Arctic Flora and Fauna (CAFF) program of the Arctic Council has outlined an international conservation strategy to conserve eiders. Individual Arctic Nations have developed and are now implementing their national eider conservation action plans with a common goal of sustaining healthy population into the future.
Four species of eider
The King Eider, Common Eider, Steller’s Eider and Spectacled Eider all breed in the Artic.
Eiders at risk
Eider and their eggs are harvested in Arctic each year. It is important to ensure that harvest levels are sustainable.
Eiders are often caught in gillnets and other fishing gear, particularly along coastlines. Changes in fishing practices are needed where this occurs.
- Contaminants and pollution
Lead poisoning and other pollution have been documented among circumpolar eider populations. This can cause death or make birds more vulnerable to disease and starvation.
Over-exploitation by man of shellfish stocks in the Dutch Wadden Sea has been linked with increasing winter mortality of Common Eiders.
- Disturbance Eider colonies attract human visitors and are sensitive to disturbance. Eiders are flightless when moulting their feathers each year, so they are also very vulnerable at this time.
- Predator control In some regions, birds and animals that eat eiders and their eggs are killed in large numbers. This activity is of conservation concern, because it can have negative impacts on species occurring with eiders.
© Daniel Bergmann
All waterfowl place down in their nests during egg laying and incubation. This is especially noticeable with the common eider. Some other diving ducks also put some down into the nest, but it is not realistic to collect it because these species nest solitarily, often attempting to hide their nests. Conversely, the common eider is a colonial nester, with tens, hundreds or even thousands of nests aggregated in demarcated areas.
Most birds develop a brood patch prior to egg laying. Feathers and down are moulted from the belly and breast in order to form a brood patch, which transfers heat from the parent to the eggs. The development of a brood patch includes a swelling of the skin, which becomes filled with white blood cells and becomes 2–5 times thicker than ordinary skin. Most importantly, the skin of the brood patch fills with blood vessels, which increase the heat flow from the parent to the eggs. Therefore, a kind of a hot plate is formed on female’s breast and belly.
Among ducks, only females incubate the eggs. They salvage the down, which falls from the brood patch, and use it to line the nest. The down covers the eggs when the duck leaves the nest and helps in maintaining correct levels of humidity and temperature in the nest. However, the down does not determine whether eggs hatch or not. Successful hatching depends mainly on how well the duck incubates her eggs. The common eider’s body condition, especially the fat reserves, determines her ability to hatch her eggs.
© Daniel Bergmann
The common eider is studied at the University of Iceland’s Snæfellsnes Research Centre. The research there is mainly concerned about population dynamics and breeding ecology, and climate change is one important research topic. Birds in the Breidafjördur Bay obtain food in shallow water, but 31% of shallow waters (20 m deep or less) in Iceland are found in Breidafjördur, along with 56% of all intertidal areas, 60% of all rockweed beds and 40% of all mudflats. Many of the biggest eider colonies in Iceland are located in Breidafjördur, especially in Vestureyjar (Flatey and nearby archipelagos) and at the mouth of Hvammsfjördur.
Ducklings have been counted yearly since 2007, and sex and age ratios (proportion of yearling drakes) have been estimated yearly since 2010. The food of the common eider has also been researched by dissecting birds incidentally caught in fishing nets.
The biggest eider project until now originated with the eider farmers themselves, at Breidafjördur, in the Southwest, in the West-fjords and in the North. For many years, eider farmers have counted the number of nests in their colonies and kept books. This data has been analysed at the Research Centre and used to evaluate whether relationships existed between weather and common eider numbers. Forty-eight eider farmers (holdings) were contacted, and 72% had numbers they lent to the project. Furthermore, the relation between weather and the arrival time of females to the colonies could be investigated at 4 colonies, as could, in one instance, the relation between the weather and the number of eggs in nests. It became possible to trace the population size development over the last 30 years (or longer) in 16 eider colonies and over a shorter time in a further 18 colonies.
Some relationships exist between the number of nests in eider colonies and the climate in Iceland with regard to the current climate change. Winters with unstable weather seem to delay nesting and negatively impact the number of eggs. Population size and the meteorological variables that affect it varied from one colony to the next. They are probably connected to a sudden change of weather and its interplay with geographical conditions in each area. Conversely, a relationship between summer weather and the number of nests 2–3 years later was discerned in 7 colonies. This indicates
that weather affects the survival of ducklings, and consequently how recruitment will be 2–3 years later (the eider is sexually mature at 2–3 years of age).
The impact of weather on the common eider in Iceland seems mostly connected with single, fateful years, such as the frost winter 1918, 1969 with its pack ice or the cold spring in 1979. Several recurrent mild winters after 1980 were actually simultaneous with an increase in eider colonies all around the country. Climate change can affect the eider’s population size, but that effect is dependent on how the weather in Iceland responds to continuing climate change. Effects of further climate change will probably be negative, should future climate change result in stormier winters in Iceland.
One could say that the project has monitored the eider backwards in time. The Snæfellsnes Research Centre intends to continue gathering this data for years to come, to monitor the common eider population.
After a somewhat stable period in 1960–1980, common eider increased from 1980–1990. This is clear both from nest figures and from the Christmas bird counts maintained by the Icelandic Institute of Natural History. After the mid-1990s, the increase seems to retreat in most parts of Iceland, although not so much in Vestureyjar in Breidafjördur.
© Daniel Bergmann
Compared to other countries, there are relatively few predator species in Iceland. The most important predators of the common eider are the Arctic fox, American mink, white-tailed sea eagle, raven and the great black-backed gull. As with other species on the island, some are very abundant and comprise large populations.
The common eider is by far the most numerous duck species in Iceland and is therefore an important part of the coastal food chain, as it preys upon various kinds of creatures and is itself an important prey of others. Eider ducklings are frequently taken by predators. A duckling mortality rate of 90% is considered normal and should not affect population size. Adult survival is, however, more important in maintaining population size than the number of ducklings that reach adulthood. Even though predation is not believed to decrease eider population size in Iceland, predators may have considerable impact on the distribution of the eider colonies and on nesting success between years and individual colonies. Through the centuries, the eider has adjusted to predation by nesting in areas with low predation pressure and has even taken refuge from predators within the nesting grounds of other species, such as seagulls. The areas in question are especially sites where the Arctic fox has limited access, such as islands.
During the last centuries, an interesting collaboration of man and eider has developed, where humans assist the eider in creating optimal nesting conditions, which in turn enable the farmer to utilise the eider colony. In many cases, this includes reducing the density of predators in defined areas. Many large colonies on the mainland owe their existence to such activity. In return, the unnaturally high density of eider under such conditions attracts even more predators, from which the farmer tries to protect the colony. The defence relies mainly on hunting the predators by shooting or trapping, but flags and human presence in the colony can sometimes be efficient in scaring the predators away. Eider farmers often invest hard work in defending their colonies.
The vast majority of the public has, to this day, been supportive of eiderdown production and the need for hunting predators in order to prevent them from causing harm to eider breeding grounds. In some cases, however, the hunting might seem to contradict natural processes, and it has been pointed out that eiderdown production, where the conditions are partly man-made, does not always justify extensive disturbance or killing of predators. Nevertheless, Icelandic legislation supports the hunting of predators, which enables profitable human exploitation of the colonies.
Here, a brief overview of the eider’s main natural enemies is given, but the list is not exhaustive.