title: Blood-specific isotopic discrimination factors in the Magellanic penguin (Spheniscus magellanicus).
abstract: The use of stable isotopes for ecological studies has increased exponentially in recent years. Isotopic trophic studies are based on the assumption that animals are what they eat plus a discrimination factor. The discrimination factor is affected by many variables and can be determined empirically. The Magellanic penguin is a highly abundant marine bird that plays a key role in the southern oceans. This study provides the first estimation of the Magellanic penguin blood discrimination factor for (13) C and (15) N.
  
  
  
  A two and a half month feeding experiment was performed, in which ten captive penguins were fed their main natural prey (anchovy Engraulis anchoita). The discrimination factors were estimated by comparing anchovy δ(13) C and δ(15) N values (obtained with isotope ratio mass spectrometry using lipid-extracted and bulk anchovy muscle) with penguin blood δ(13) C and δ(15) N values.
  
  
  
  Penguin blood was shown to be enriched, compared with anchovies, for (13) C and (15) N. No changes were observed in the stable isotope ratios of anchovies and discrimination factors during the experiment. The overall discrimination factors were 0.93 ± 0.12 (bulk) and 0.41 ± 0.12 (lipid-free) for (13) C; and 2.81 ± 0.17 (bulk) and 2.31 ± 0.17 (lipid-free) for (15) N.
  
  
  
  Having an accurate discrimination factor for the studied species is key in any trophic or food web isotopic study. Comparisons of estimated diet-to-blood discrimination factors with published values of aquatic piscivore birds showed that the (13) C discrimination factor is particularly variable, and therefore ecologists should be cautious when using a surrogate value from other species. In this study, the Magellanic penguin discrimination factor of a tissue that does not require euthanasia was obtained, a fundamental input for trophic isotopic modeling of the species. Copyright © 2016 John Wiley & Sons, Ltd.
authors.affiliation: IBIOMAR Centro Nacional Patagónico--CONICET, Blvd. Brown 2915, CP 9120, Puerto Madryn, Chubut, Argentina.
authors.forename: Javier E
authors.initials: JE
authors.lastname: Ciancio
authors.affiliation: Fundacion Temaikèn Departamento de Conservación e Investigación, Ruta 25, Km 0.7 Belén de Escobar, CP, 1625, Buenos Aires, Argentina.
authors.forename: Carina
authors.initials: C
authors.lastname: Righi
authors.affiliation: Aquarium Mar del Plata, Av. Martínez de Hoz 5600, CP 7600, Mar del Plata, Buenos Aires, Argentina.
authors.forename: Adrián
authors.initials: A
authors.lastname: Faiella
authors.affiliation: Centro de investigaciones Puerto Deseado (UNPA-CONICET) and BirdLife International (Marine Programme), Costanera Lotufo s/n, CP 9050, Puerto Deseado, Santa Cruz, Argentina.
authors.forename: Esteban
authors.initials: E
authors.lastname: Frere
mesh_terms: D000818:Animals; D002247:Carbon Isotopes / Q000097:blood*; D005247:Feeding Behavior / Q000502:physiology; D005260:Female; D020387:Food Chain; D008297:Male; D009587:Nitrogen Isotopes / Q000097:blood*; D010473:Perciformes; D046429:Spheniscidae / Q000097:blood* / Q000502:physiology*
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes