King eiders use an income strategy for egg production: a case study for incorporating individual dietary variation into nutrient allocation research

Abstract

The use of stored nutrients for reproduction represents an important component of life-history variation. Recent studies from several species have used stable isotopes to estimate the reliance on stored body reserves in reproduction. Such approaches rely on population-level dietary endpoints to characterize stored reserves ("capital") and current diet ("income"). Individual variation in diet choice has so far not been incorporated in such approaches, but is crucial for assessing variation in nutrient allocation strategies. We investigated nutrient allocation to egg production in a large-bodied sea duck in northern Alaska, the king eider (Somateria spectabilis). We first used Bayesian isotopic mixing models to quantify at the population level the amount of endogenous carbon and nitrogen invested into egg proteins based on carbon and nitrogen isotope ratios. We then defined the isotopic signature of the current diet of every nesting female based on isotope ratios of eggshell membranes, because diets varied isotopically among individual king eiders on breeding grounds. We used these individual-based dietary isotope signals to characterize nutrient allocation for each female in the study population. At the population level, the Bayesian and the individual-based approaches yielded identical results, and showed that king eiders used an income strategy for the synthesis of egg proteins. The majority of the carbon and nitrogen in albumen (C: 86 +/- 18%, N: 99 +/- 1%) and the nitrogen in lipid-free yolk (90 +/- 15%) were derived from food consumed on breeding grounds. Carbon in lipid-free yolk derived evenly from endogenous sources and current diet (exogenous C: 54 +/- 24%), but source contribution was highly variable among individual females. These results suggest that even large-bodied birds traditionally viewed as capital breeders use exogenous nutrients for reproduction. We recommend that investigations of nutrient allocation should incorporate individual variation into mixing models to reveal intraspecific variation in reproductive strategies.

Isotopic ornithology: a perspective

“…For example, Oppel et al (2010) investigated capital vs. income breeding in King Eiders (Somateria spectabilis), and Hobson et al (2011a) used identical Bayesian approaches to examine isotope data on eggs and body tissues of the High Arctic Greater Snow Goose (Chen caerulescens atlantica) population used by Gauthier et al (2003) and of two sub-Arctic populations of Lesser Snow geese (Chen caerulescens caerulescens). Both studies provided a sensitivity analysis over a wide range of assumed endogenous to egg d 15 N discrimination values.…”

Full Issue

“…Among waterfowl, the large-bodied eiders have been considered to be capital breeders (Parker and Holm 1990, Kellet and Alisauskas 2000, Nolet 2006, Bentzen et al 2008; however, evidence is mounting that previous assumptions regarding the life-history characteristics of migratory birds may need to be revisited. This is especially true for assumptions of capital breeding because this lifehistory strategy is likely less common in migratory birds than previously believed (Gauthier et al 2003, Oppel et al 2010, Sénéchal et al 2011, Sharp et al 2013. The relative importance of nutrients derived from the breeding vs. wintering grounds is crucial for predicting how the breeding success of migrating birds responds to changes in food availability during any part of their annual cycle.…”

Anseriforme Husbandry and Management

“…While it has been reported that Brent geese (Branta bernicla) forage an average of 3 hours a day, data on the specific amount of time most waterfowl spend foraging is lacking [64]. Ducks may not use a foraging device if the food is too difficult to obtain.…”