Common Eiders

Great Duck Island is probably named for the vast flocks of eider ducks that used to be seen using the island’s shoreline as a nursery.  Our high count from the tower this year was 174, down dramatically from the 2002 high count of 1,120 eiders we found only 9 nests on the island — most of the females and chicks that come to Great Duck’s intertidal are probably from nearby Little Duck Island, which has no history of permanent human settlement.

Eiders have a very short courtship period in late spring, after which the males move off-shore to exclusive “bachelor clubs” while the females seek out islands to lay their eggs. Eider nests are masterpieces of thermal insulation — the female eider lines the nest with a thick layer of down, and weaves a down coverlet for the top that serves to both insulate the developing embryos and camouflage the nest from predators. In the Far north, Eider nests are traditionally collected at the beginning of the season as filling for down coats, comforters, sleeping bags, etc. So long as the nest is only taken once, the female will rebuild it and continue incubation. In Maine and parts of Europe eiders are only found nesting on islands that have populations of Herring gulls or active human control of predators. There is evidence that the gulls serve as deterrents to crows and ravens, who would destroy a whole clutch if they were to come upon a nest.

Once hatching occurs the female eider leads the chicks away from the nest site and guards them in an extended “creche” along the rocky intertidal. Some females appear to abandon their chicks entirely, while others adopt “orphans” to form clusters of 2-20+ chicks. Contrary to studies at other islands, we have found little evidence of predation by gulls on eider chicks. In hundreds of hours of observation of groups of eider females and chicks from the lighthouse tower we have seen a total of less than 30 attacks by Black backed gulls, most of which were broken off without loss of a chick after an aggressive response from eider adults. We have seen only two attacks by Herring gulls. Of more concern is predation by seals, who have been appearing in increasing numbers around the south end of Great Duck over the past two decades. We have also seen adult eiders attacked on the water by Bald Eagles.  Eider numbers are dropping dramatically state wide, in tandem with gull declines.  We suspect that this is due to a combination of predation, disturbance, loss of food, and over-hunting.

Type

Fauna

Scientific Name

Somateria mollissima