aus: NAUMANN : Naturgeschichte der Vögel Mitteleuropas, Band VI, Tafel 21 - Gera, 1897 digitale Bearbeitung : Peter v. Sengbusch - b-online@botanik.uni-hamburg.de
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Naumann, Naturgeschichte der Vögel Mitteleuropas. 3. Aufl. Neubearb. von G. Berg et al. Hrsg. von Carl R. Hennicke. (Naumann, Natural history of the birds of central Europe, 3rd Ed. Revised by G. Berg et al.; Edited by Carl R. Hennicke.) of 1905 or his earlier works.
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