2 literature references for Tetrao urogallus Ingram, 1915:

Author: Dickinson, Edward C., ed.
Year: 2003
Title:
Source: The Howard and Moore Complete Checklist of the Birds of the World, 3rd edition
Author:
Year: 2005
Title:
Source: website, Zoonomen - Zoological Nomenclature Resource, 2005.05.23