Differential contributions of endogenous and exogenous nutrients to egg components in wild Baltic Common Eiders (Somateria mollissima): A test of alternative stable isotope approaches

Abstract

The relative importance of nutrients derived from feeding on breeding vs. nonbreeding grounds to the formation of eggs is crucial for predicting how the breeding success of migrating birds responds to changes in food availability during any part of their annual cycle. Eiders have been considered a classical capital breeder, but this assumption has rarely been tested. The measurement of naturally occurring stable isotopes in egg components, together with those in endogenous and exogenous nutrient endpoints, allow the estimation of the relative sources of nutrients to eggs, but these mixing models rely critically on appropriate isotopic discrimination factors that link egg isotope values with their source. A recent captive study using Spectacled Eiders (Somateria fischeri) provided estimates of these isotopic discrimination factors for income breeding. We applied these discrimination factors for investigating nutrient allocation strategies in Common Eiders (Somateria mollisima) breeding in the northern Baltic (Tvärminne, Finland) and wintering in Danish waters, sourced during 2009-2012. Our overall estimates of protein sources using isotopic mixing models were mixed for egg yolk (median: 44.5-56.5% endogenous) and overwhelmingly exogenous for egg albumen (0.4-0.7%). We tested our conclusions also with a single (d 15 N) model and with a more parsimonious d 13 C discrimination factor between diet and egg albumen, and both supported little to no endogenous reserves being used for egg albumen. A strong positive correlation between egg lipid d 13 C and lipid-free yolk d 13 C suggests similar metabolic pathways between diet sources and these egg macromolecules. The applicability of isotope discrimination factors used in nutrient allocation studies derived from captive populations needs to be tested in wild populations. Our results support the idea that potential food limitation not only at the wintering areas, but also at the breeding grounds, can limit breeding success of Baltic Common Eiders, which are currently declining.Contribución diferencial de nutrientes endógenos y exógenos a los componentes del huevo de individuos silvestres de Somateria mollissima: evaluación de enfoques alternativos de isótopos estables RESUMEN La importancia relativa de los nutrientes derivados de la alimentación en los sitios reproductivos y no reproductivos para la formación de los huevos es crucial para predecir cómo eléxito reproductivo de las aves migratorias responde a los cambios en la disponibilidad de alimentos durante cualquier parte de su ciclo anual. Somateria mollissima ha sido considerada como un ave criadora de capital clásica, pero este supuesto muy pocas veces no ha sido evaluado. La medición de isótopos estables naturales en los componentes del huevo, junto a la de los puntos finales de nutrientes endógenos y exógenos, permite estimar las fuentes relativas de nutrientes de los huevos, pero estos modelos duales dependen de modo crítico de los factores de discriminación de isótopos apropiados que vinculan los valores isotópic...

Seasonal reproductive tactics: annual timing and the capital-to-income breeder continuum

“…Whereas small migratory birds are typically reliant on capital only to fuel migration (but see [88]), many larger migrants are capital or mixed-strategy breeders [4,5,21]. Highlatitude-breeding migratory waterfowl by and large track a successively delayed spring flush of plants on their way from the wintering grounds in the temperate zone to their Arctic breeding grounds, leading to the expression that they 'surf the green wave' [89].…”

Dynamic group size and displacement as avoidance strategies by eiders in response to hunting

“…The daily food demand by eiders increases from autumn to winter from 2.2  10 6 J to 2.9  10 6 J (Brinkman et al 2003), and the weight of the females increase accordingly (Milne 1976), when they build up body resources on the wintering grounds for subsequent breeding (Descamps et al 2011, Sénéchal et al 2011, Hobson et al 2015, Waltho and Coulson 2015. Individual eiders arriving at the breeding grounds in prime condition produce larger clutches with higher duckling survival than individuals in poor condition (Hanssen et al 2002, Hario and Selin 2002, Öst et al 2008).…”

State-dependent capital and income breeding: a novel approach to evaluating individual strategies with stable isotopes

“…A major discovery in the wake of this research is that capital breeders, particularly migratory ones, often rely more on concurrent intake than previously assumed, presumably because of the costs of carrying excess stores (e.g. [ 5 , 6 ]). These improvements have moved us beyond the overly simplistic capital-income typology and have increased our understanding of the drivers of this variation in nutrient sources contributing to reproductive investment at the species level.…”