Amino Acid Specific Stable Nitrogen Isotope Values in Avian Tissues: Insights from Captive American Kestrels and Wild Herring Gulls

Abstract

Through laboratory and field studies, the utility of amino acid compound-specific nitrogen isotope analysis (AA-CSIA) in avian studies is investigated. Captive American kestrels (Falco sparverius) were fed an isotopically characterized diet and patterns in δN values of amino acids (AAs) were compared to those in their tissues (muscle and red blood cells) and food. Based upon nitrogen isotope discrimination between diet and kestrel tissues, AAs could mostly be categorized as source AAs (retaining baseline δN values) and trophic AAs (showing N enrichment). Trophic discrimination factors based upon the source (phenylalanine, Phe) and trophic (glutamic acid, Glu) AAs were 4.1 (muscle) and 5.4 (red blood cells), lower than those reported for metazoan invertebrates. In a field study involving omnivorous herring gulls (Larus argentatus smithsonianus), egg AA isotopic patterns largely retained those observed in the laying female's tissues (muscle, red blood cells, and liver). Realistic estimates of gull trophic position were obtained using bird Glu and Phe δN values combined with β values (difference in Glu and Phe δN in primary producers) for aquatic and terrestrial food webs. Egg fatty acids were used to weight β values for proportions of aquatic and terrestrial food in gull diets. This novel approach can be applied to generalist species that feed across ecosystem boundaries.

Compound‐specific 15N analysis of amino acids: A tool to estimate the trophic position of tropical seabirds in the South China Sea

“…We first analyze the TEFs in AAs between bird and fish bones to preliminarily discuss the tissue‐specific isotopes including AAs isotopes for seabirds and fish. The TEF values (Figures and ) between tropical seabird and flying fish bone AAs δ 15 N or δ 13 C values were quite different from those reported in previous studies of birds (Hebert et al., ; McMahon et al., ). For example, the avian‐specific nitrogen TEF of Glu was higher (TEF Glu = 3.8 ± 0.6‰) in previous study (McMahon et al., ).…”

“…Recently, Hebert et al. () also found that the TDFs based upon the source (Phe) and trophic (Glu) AAs were 4.1 and 5.4 for muscle and red blood cells, respectively, from laboratory and field studies of captive American kestrels and wild herring gulls. This was lower than the values reported for metazoan invertebrates.…”

Stable Isotopes from Museum Specimens May Provide Evidence of Long-Term Change in the Trophic Ecology of a Migratory Aerial Insectivore

“…With this in mind, we suggest that rather than attempting to sample lower trophic levels by sampling prey species directly, future studies should use a comparative approach and sample species with different diets, but similar scales of movement and geographic distribution of their food sources (Thompson et al, 1995). Alternatively, as compound-specific stable-isotope analyses become more affordable, it will be possible to determine baseline values and thereby more accurately assess trophic-level from within a single tissue sample (McMahon et al, 2015;Hebert et al, 2016;Ostrom et al, 2017).…”

Diet of the prehistoric population of Rapa Nui (Easter Island, Chile) shows environmental adaptation and resilience

“…In order to estimate the fraction of marine protein ( f marine ) in human diets, we used an amino acid nitrogen isotope mass balance model that combines Equations (1) and (2) (see also Hebert et al, 2016; Styring, Fraser, Bogaard, & Evershed, 2014). This approach uses a β mixed value, which multiplies the estimated fraction of marine and terrestrial foods ( f marine and 1‐ f marine , respectively) with their corresponding known marine or terrestrial β values.…”