Reference

Siegfried Klaus, Alexander V. Andreev, Michael A. Schroeder, Christoph Unger (2019): Kurze Mitteilungen Sickle-shaped primaries and tail feathers involved in sound production in Siberian Grouse Falcipennis falcipennis Hartlaub 1855 – Ornithologischer Anzeiger – 58_1: 48 - 53.