title: 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 δ15N 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 δ15N values) and trophic AAs (showing15N 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 δ15N values combined with β values (difference in Glu and Phe δ15N 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.
authors: Environment and Climate Change Canada, Science and Technology Branch, National Wildlife Research Centre , Ottawa, ON K1A 0H3, Canada.
authors: C E
authors: CE
authors: Hebert
authors: Department of Geology and Geophysics, University of Hawaii , Honolulu, Hawaii 96822, United States.
authors: B N
authors: BN
authors: Popp
authors: Environment and Climate Change Canada, Science and Technology Branch, Canada Centre for Inland Waters , Burlington, ON L7R 4A6, Canada.
authors: K J
authors: KJ
authors: Fernie
authors: Department of Geology and Geophysics, University of Hawaii , Honolulu, Hawaii 96822, United States.
authors: C
authors: C
authors: Ka'apu-Lyons
authors: United States Geological Survey, Patuxent Wildlife Research Center , Beltsville, Maryland 20705, United States.
authors: B A
authors: BA
authors: Rattner
authors: Department of Geology and Geophysics, University of Hawaii , Honolulu, Hawaii 96822, United States.
authors: N
authors: N
authors: Wallsgrove
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D002247:Carbon Isotopes; D046091:Charadriiformes / Q000378:metabolism*; D020387:Food Chain; D009584:Nitrogen; D009587:Nitrogen Isotopes; D014481:United States
chemical_list: D000596:Amino Acids; D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D009584:Nitrogen