Nutrient acquisition and allocation strategies for reproduction by female Harlequin Ducks

I analysed body mass variation and stable isotope signatures (615~, 613c) of adult female Harlequin Ducks (Histrionicus histrionicus) on marine wintering areas and freshwater breeding streams in southern British Columbia to investigate when and where they acquire nutrients prior to reproduction and the sources of nutrients allocated to clutch formation. I found that female body mass on wintering grounds increased by 7% in the weeks before migration, irrespective of whether they were consuming their usual winter diet of intertidal invertebrates or superabundant spawn of Pacific herring (Clupea pallasi). However, stable isotope analyses revealed that freshwater nutrients, not marine, were allocated to eggs, and therefore, stored marine nutrients were likely used during other reproductive stages. I also estimated breeding propensity of Harlequin Ducks using a novel method combining yolk precursor analyses and radio telemetry, and estimated that 92% of females on streams initiated egg formation