Correlated Growth and Survival of Juvenile Spectacled Eiders: Evidence of Habitat Limitation?

Abstract We studied the growth andsurvival of Spectacled Eider (Somateriafischeri) ducklings to30 days of age along the lower KashunukRiver on the Yukon-Kuskokwim Delta from 1995 to2000. We replicated this study at a second site,Kigigak Island, in 1999 and 2000. Age-adjustedestimates of duckling mass and survival at30 days posthatching were highly variable.Duckling survival was consistently higher onKigigak Island in 1999 and 2000, averaging67%, while survival on the Kashunuk Riveraveraged 45% during the same time period.Duckling survival was negatively related tohatching date. At the Kashunuk River site our datasupported models that indicated age-adjusted massvaried with habitat type and declined with hatchingdate. Ducklings from Kashunuk River were heavier in1999, while ducklings from Kigigak Island wereheavier in 2000. However, we found a positivecorrelation between 30-day duckling survival andage-adjusted mass, suggesting a localizedenvironmental effect on both parameters. Weconclude that predation may be the proximatemechanism of mortality, but habitat conditions arelikely the ultimate factors influencing ducklingsurvival. Geographic variation in rates of ducklingsurvival and apparent growth suggest that spatialheterogeneity in population vital rates isoccurring at multiple levels.