Do purely capital layers exist among flying birds? Evidence of exogenous contribution to arctic-nesting common eider eggs

Abstract

The strategy of relying extensively on stored resources for reproduction has been termed capital breeding and is in contrast to income breeding, where needs of reproduction are satisfied by exogenous (dietary) resources. Most species likely fall somewhere between these two extremes, and the position of an organism along this gradient can influence several key life-history traits. Common eiders (Somateria mollissima) are the only flying birds that are still typically considered pure capital breeders, suggesting that they depend exclusively on endogenous reserves to form their eggs and incubate. We investigated the annual and seasonal variation in contributions of endogenous and exogenous resources to egg formation in eiders breeding at the East Bay colony in the Canadian Arctic. We collected prey items along with females and their eggs during various stages of breeding and used two complementary analytical approaches: body reserve dynamics and stable isotope [δ(13)C, δ(15)N] mixing models. Indices of protein reserves remained stable from pre-laying to post-laying stages, while lipid reserves declined significantly during laying. Similarly, stable isotope analyses indicated that (1) exogenous nutrients derived from marine invertebrates strongly contributed to the formation of lipid-free egg constituents, and (2) yolk lipids were constituted mostly from endogenous lipids. We also found evidence of seasonal variation in the use of body reserves, with early breeders using proportionally more exogenous proteins to form each egg than late breeders. Based on these results, we reject the hypothesis that eiders are pure capital layers. In these flying birds, the fitness costs of a strict capital breeding strategy, such as temporary loss of flight capability and limitation of clutch and egg size, may outweigh benefits such as a reduction in egg predation rate.

Unpredictable perturbation reduces breeding propensity regardless of pre‐laying reproductive readiness in a partial capital breeder

“…As such, by mimicking a momentary Gorman et al 2009). In common eiders, VTG has been found to have a threshold relationship to body mass (Hennin et al 2015), a key driver of reproductive decisions in these birds (Sénéchal et al 2011). As such, plasma VTG may play an important role with body mass in predicting the ability Table 1.…”

“…Arctic-breeding common eiders are income-capital breeders that feed intensively during the pre-breeding and laying periods, and depend heavily on endogenous stores to produce their eggs and successfully complete their 24 d-long incubation fast (Sénéchal et al 2011). Our study demonstrates that pre-breeding body condition is a key driver of breeding propensity in this mixed-strategy breeder.…”

“…By knowing the initial state of pre-laying individuals through plasma VTG (individuals engage in egg formation or not), our experiment can contribute to testing components of the condition dependent individual optimization model (McNamara andHouston 1996, Ricklefs andWikelski 2002). Common eiders are a good model system to test these relationships because: 1) they are a long-lived, migratory species which exhibit a capital-income breeding strategy, 2) previous studies have shown that reproductive decisions were influenced by a body mass (Sénéchal et al 2011, Hennin et al 2015 threshold, and 3) if females cannot achieve a threshold body mass early enough in the breeding season to successfully complete reproduction, they have the flexibility within their life history to skip reproduction in favour of self-maintenance for that year (Yoccoz et al 2002). We predicted that females that are heavier and have higher plasma VTG (likely closer to laying), would have a higher breeding propensity.…”

Carbon isotopic fractionation in eider adipose tissue varies with fatty acid structure: implications for trophic studies

“…Reproductive problems and low productivity have been documented for both species (Grand et al, 2002;Rojek, 2008). In Steller's and spectacled eiders, the relative importance of marine and terrestrial nutrients for reproduction is unknown, but there is evidence to suggest that some sea duck species acquire nutrients for successful breeding from both the terrestrial nesting and marine staging grounds (Bond et al, 2007;Sénéchal et al, 2011). A better understanding of diet sources and timing of nutrient acquisition for these eiders will provide information to help identify important pre-breeding habitats of threatened eider populations in Alaska.…”

The early birds and the rest: do first nesters represent the entire colony?

“…Common eider responds to climate change because females that attain the best body condition in late winter generally become the first nesters in a given year (Bolduc et al 2005;Ö st et al 2008) and earlier nesting generally is positively related to hatching success (Ö st et al 2011), more exogenous protein use for egg formation relative to later nesters (Sénéchal et al 2011), and increased clutch sizes Jónsson et al 2009;Mehlum 2012). Unfavorable winter weather can interfere with accumulation of endogenous reserves for breeding, cause nest desertion and affect levels of yolk hormone, nest site selection or immune function (Robertson 1995;Descamps et al 2010;Love et al 2010;Sénéchal et al 2010;Jónsson and Lúðvíksson 2013).…”