Use of amino acid isotope analysis to investigate capital versus income breeding strategies in migratory avian species

Income and capital breeding represent opposing ends of a continuum reproductive strategies. Quantifying nutrient allocation to reproduction is challenging, but recent advances in compound-specific stable isotope analysis hold promise for tracing the source individual compounds allocated reproduction. Here, we describe novel approach using measured carbon (δ13C) nitrogen (δ15N) values amino acids (AAs) pectoral muscle egg-laying females egg yolk as useful tool quantify reliance on income versus migrating species. We used white-fronted (Anser albifrons frontalis), lesser snow (A. caerulescens caerulescens) black brant (Branta bernicla nigricans) geese tundra ecosystems northern Alaska model organisms. All three species relied mixed capital–income strategies, models based AA data estimated higher proportional contributions endogenous resources synthesis compared results bulk tissue analyses. Tracing migratory at compound level major advance from current ‘elemental’ perspective obtained Our framework applicable all taxonomic groups, long there sufficient spatial or temporal isotopic gradient between during non-breeding periods.