Status of the common eider (Somateria mollissima) in New Brunswick

Mawhinney, Kim
Diamond, A.W.

In 1995 we conducted a pilot study of brood ecology of the Common Eider Somateria mollissima with specific reference to movements, habitat use and behaviour of both adult females and ducklings on the Wolves Archipelago in the Bay of Fundy. Information generated from this colony, particularly recruitment, over the next 3 years was to be used in conjunction with information collected from other breeding colonies to develop a model of the role of post-hatch ecology in the demographics of Common Eiders in the Bay of Fundy. Exceptionally high depredation rates by Great Black-backed Gulls Larus marinus on Eider ducklings precluded the study of brood amalgamation as only 12 of 3000 ducklings produced in this colony fledged. In 1996 breeding pairs of Great Black-backed Gulls were eliminated on two of the five islands in the Archipelago and clutches were prevented from hatching on two other islands. Great Black-backed Gulls on clutches that were oiled to prevent hatch had a protracted incubation period, and the absence of chicks did not reduce adult Great Black-backed Gull depredation on Eider broods as only 8 ducklings fledged.Duckling mortality on the Wolves Archipelago exceeded 95% in both 1995 and 1996. Brood surveys suggested that low duckling production was not confined to the Wolves Archipelago; and that duckling production in the Bay of Fundy has declined considerably over the last decade despite stable numbers in breeding pairs. High duckling mortality is a common phenomenon in Eiders and survival of ducklings does not apparently regulate Common Eider population numbers; however, it may potentially limit the growth rate of the population. Although the numbers of Common Eiders breeding in New Brunswick appear stable, we cannot be complacent; low annual recruitment over periods of several years has been associated with gradual declines in breeding populations of Common Eiders elsewhere.