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- © Arnaiz-Villena, A; Areces C, Rey D, Enríquez-de-Salamanca M, Alonso-Rubio J and Ruiz-del-Valle V (2012). "Three Different North American Siskin/Goldfinch Evolutionary Radia-tions (Genus Carduelis): Pine Siskin Green Morphs and European Siskins in America". The Open Ornithology Journal 5: 73-81.doi:10.2174/1874453201205010073.
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- Provenance: http://media.eol.org/content/2015/03/20/15/04060_orig.jpg