Habitat and Artificial Shelter Use by American Eider, Somateria Mollissima Dresseri (Sharpe) Nesting on the Eastern Shore of Nova Scotia

Résumé du livre

American Eider nesting habitats were studied within the Eastern Shore Islands Wildlife Management Area of Nova Scotia in 1992 and 1993. The importance of island size, distance to the mainland and presence of other nesting seabirds to nesting eider were investigated at an island scale. The use of natural cover types, the value of artificial shelters as alternative nesting sites and the reproductive importance of natural cover types and artificial shelters were all examined. Islands surveyed ranged from 0.8 to 14.8 hectares in size and from 1.3 to 7.1 kilometres in distance from the mainland. Neither characteristic was an accurate predictor of eider nesting populations. Eiders and gulls nested on the same islands in the WMA. Gull presence did not appear to limit eider nesting populations. The largest proportion of nests were recorded for shrub growth of gooseberry. Nests were sparsely scattered in barren cover while beach and forest cover were generally avoided as nesting cover. Deadfalls were particularly important for nests in sparse vegetative cover, with 59% of nests in barren cover recorded under deadfalls. Low shelter use (0 to 1.4%) on most islands was attributed to the placement of shelters in cover normally avoided by eiders. Use of shelters was much higher (38%) on Inner East Bird Island where shelters were located throughout tall grasses and ferns. There was a high rate of reuse of nesting sites under shelters in consecutive years. Clutch sizes were significantly lower in beach cover than under gooseberry cover. Nests in the least favored cover types were the most vulnerable to predation. Overall nest loss was 16% in 1992 and 17% in 1993. Nests under beach cover were the most vulnerable while nests under tuckamoor and shelters were most likely to hatch successfully.