An Etymological Dictionary of the German Language/Auerhahn
Auerhahn, m., even in MidHG. the equiv. ûrhan (and orhan), m., ‘blackcock,’ with ûrhuon (orhuon), ‘grey hen,’ occurs. Auerhahn was evidently compared with Auerochs, the one appeared to be among the birds of the wood what the other was among animals of the chase.