I assessed the relative importance of criteria governing selection of Common Eider (Somateria mollissima) brood-rearing habitat on mainland New Brunswick in 2000 and Grand Manan Island in 2001. I quantified the influence of rockweed (Ascophyllum nodosum) harvesting and other factors on duckling abundance and distribution. Scan sampling was conducted from June-August in both years for a total of 1431 hours.

The majority (71-85%) of ducklings recorded were >2 weeks old in spite of an early start to observations. Duckling numbers increased by 10.5 individuals with an increase from 0-1500 eider nests on colonies <5 km away, but only in sites furthest away from breeding colonies of Great Black-backed Gulls (Larus marinus). Negative relationships emerged between numbers of ducklings, and both Great Black-backed and Herring Gulls (L. argentatus) in both study areas. Kleptoparasitism on older ducklings and adults by gulls may have resulted in avoidance of gulls by eiders. Bald Eagles (Haliaeetus leucocephalus) were responsible for 10 out of 13 ducklings seen captured.

Sites with a gradual slope supported 43-85% more ducklings in all age groups on the mainland, possibly by offering increased surface-feeding area. Neither rockweed density nor height, substrate type, aspect, degree of exposure nor regional differences were found to be important criteria for selection of habitat. Green Crab (Carcinus maenas) may have been an important prey for older ducklings in this system.
Statistical power was too low to detect a meaningful effect of rockweed harvesting on brood distribution or on their feeding habitat. However, declines in duckling numbers were associated with 50-fold increases in both boat (-2.2 ducklings) and shore-based traffic (-2.9) on Grand Manan Island. Consequently, further research is necessary to establish potential effects of disturbance on eider broods by harvesting.

Funding provided by the New Brunswick Wildlife Trust Fund

Logistical support provided by Acadian Seaplants, Ltd.