| Summary: | Thesis (M.Sc.)--Memorial University of Newfoundland, 1999. Biopsychology Bibliography: leaves 179-194. Seabirds forage in a variable environment. Theoretical investigations into seabird foraging ecology and practical efforts to utilize seabirds as sampling agents of marine dynamics have been hampered by an inadequate base of natural history data. Prior to this studyt the nestling diets of Atlantic Puffins along the coast of insular Newfoundland in the northwest Atlantic were assumed to be homogeneous. successful breeding by Atlantic Puffins in the region had been linked to the availability of mature capelin which was thought to be an essential component of puffin nestling diet due to the paucity of suitable alternative prey. -- This study reports data on the diets and condition of nestlings collected at Baccalieu, Funk and Small Islands between 1992 and 1995. Bill-loads of fresh prey were collected from adult Atlantic Puffins provisioning nestlings. Bill-load size and the contribution to the diets made by mature capelin were compared between areas and years in conjunction with nestling condition, measured as body mass at a given wing-length. Proximate organic composition analyses were conducted on the lesser known prey items and energy densities estimated. -- These data were used to test the assumptions that 1) the diets of puffin nestlings along the coast of insular Newfoundland are homogeneous and 2) that there are no prey of comparable quality to mature capelin available to breeding puffins in the region. The data do not support either assumption. Diets of nestling puffins along the northeast coast of insular Newfoundland are not homogeneous. Rather than uniformly dominated by mature capelin, the diets of nestling puffins on Funk and Small Islands were sometimes composed principally of either postlarval O-group sandlance or larval 1-group capelin. The condition of nestlings fed on post-larval O-group sandlance was the best observed in this study, exceeding that of nestlings fed diets dominated by mature capelin. 1-group capelin had a wet energy density similar to male capelin while postlarval O-group sandlance had a wet energy density which exceeded that of mature capelin during a comparable time of year. -- I conclude that the diets of Atlantic Puffin nestlings in the northwest Atlantic are more variable than previously considered, and that there are occasions when prey of at least comparable energetic density to that of mature capelin are available to adult puffins provisioning young in this region.
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