Quantifying capital vs. income breeding: new promise with stable isotope measurements of individual amino acids

1. Capital breeders accumulate nutrients prior to egg development, then use these stores to support offspring. In contrast, income breeders rely on local nutrients consumed contemporaneously with offspring development. Understanding such nutrient allocations is critical to assessing wildlife reliance on different habitats.

2. Despite the contrast between these strategies, it remains challenging to trace nutrients from endogenous stores or exogenous food intake into offspring. Here, we tested a new solution to this problem.

3. Using tissue samples collected opportunistically from wild emperor penguins (Aptenodytes forsteri), which exemplify capital breeding, we hypothesized that the stable carbon (δ13C) and nitrogen (δ15N) isotope values of individual amino acids (AA) in endogenous stores (e.g., muscle) and in egg yolk and albumen reflect the nutrient sourcing that distinguishes capital versus income breeding. Unlike other methods, this approach does not require untested assumption...