PARENT SESSION
Poster Session 28: Avian Ecology
Thursday, August 11, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal
Distribution of Common Eiders during brood-rearing in the St. Lawrence estuary.
Diéval, Hélène*,1, Giroux, Jean-François1, Savard, Jean-Pierre2, 1 Université du Québec à Montréal, Montréal, Qc, Canada2 Environnement Canada, Service canadien de la faune, Ste-Foy, Qc, Canada
ABSTRACT- Common Eiders (Somateria mollissima dresseri) nest in colonies on islands of the St. Lawrence estuary in Quebec. After hatching, females must reach adequate habitats for rearing their ducklings. Adult birds also undertake a moult in late summer but their distribution is not well known. The aim of our study was to determine the biotic and abiotic factors that influence the distribution of these birds during the brood-rearing and moulting periods. The number of Common Eiders was recorded by age and sex bi-weekly in 2003 and 2004 at 68 sites located along a 200-km stretch of the south shore of the St. Lawrence River. For adult females, we also noted whether they were accompanied by young or not. In 2004, we recorded the behaviour of individuals and noted their locations on the water. We developed a human disturbance index, characterized the nature of the substrate, and estimated food abundance. At the scale of the estuary, Common Eiders did not distribute randomly and used the same sites in both years. Females without ducklings and males were found further east along the estuary, but their number was lower than expected. In parallel, broods preferred the westerly areas near the nesting islands. On a temporal scale, we observed that the densities of females without ducklings increased significantly during the summer as they move eastward. Broods spent more than half of the day time feeding while this proportion decreased through time from nearly 40% to 10% for adults without ducklings. On a local scale, broods used mainly the intertidal zone whereas adults without ducklings were distributed further off-shore. Food abundance was the best variable to describe the distribution of Common Eiders along the shore while human disturbance had little effect, which was contrary to our expectations. In conclusion, our study will help to identify the best brood rearing and moulting sites for Common Eiders along the St. Lawrence estuary. Very few of these sites are included within conservation areas and measures should be taken to insure their protection.
Key words: habitat selection, sea duck, brood-rearing, environmental factors