The common Eider duck
With their superb plumage and distinctive, endearing calls, eiders are a much-loved sight around the coast of Arran.
In the breeding season, the male is easily identified by his pristine black and white plumage, beautifully complemented by a subtle green nape and a soft pinkish flush on his white chest feathers. By contrast, the female is brown with an intricately barred pattern, ideal colours for sitting camouflaged on a nest on the ground.
The common eider, somateria mollissima, is Britain’s heaviest duck, weighing between 1.5 and 2.5kgs and with a body length of up to 71 cms. It’s also the largest duck in the northern hemisphere.
Surprisingly, it’s also the UK’s fastest duck in flight, with speeds of up to 60 mph. The scientific name of the duck is derived from ancient Greek somatos ‘body’ and erion ‘wool’, and Latin mollissimus ‘very soft’, all referring to its down feathers.
The female eider lines her nest with down feathers plucked from her breast. In Iceland, where the feathers are harvested, the contents of 85 nests will fill one duvet. Eiderdown harvesting continues and is sustainable, as it can be done after the ducklings leave the nest with no harm to the birds.
In AD 676, the colony of eiders on the Farne Islands was protected by St Cuthbert who introduced one of the first bird protection laws. The birds still bear his name. Around the Northumberland coast, where they still breed in their thousands, they’re known as ‘cuddy ducks’.
Eiders feed on crustaceans and molluscs. Mussels are their favourite food, which is why they’re often seen around mussel farms. They swallow the shellfish whole, and the shells are crushed in their stomach.
Eiders are colonial breeders. They nest on coastal islands in colonies ranging in size of less than 100 to upwards of 10,000 to 15,000 individuals.
Female eiders frequently exhibit a high degree of natal philopatry, where they return to breed on the same island where they hatched. This can lead to a high degree of relatedness between individuals nesting on the same island, as well as the development of kinbased female social structures.
This relatedness has likely played a role in the evolution of co-operative breeding behaviours amongst eiders.
Examples of these behaviours include laying eggs in the nests of related individuals and crèching, where female eiders team up and share the work of rearing ducklings. Male Eiders, on the other hand, while they are energetic in their display when courting, take little or no part in rearing the young.
Eiders are familiar birds around the Arran coast but their numbers are declining, not only around Arran but in the entire Firth of Clyde. Chris Waltho, a past president of the Scottish Ornithologists Club, has organised September surveys in the Clyde for about 20 years. Data compiled by Chris shows that the post breeding population of eiders in the Firth of Clyde is in decline.
Bird notes by Jim Cassels MAY