As to the "Eule(n)", a transformation of an older, Slavic word seems more likely: See "Historia" here
Thanks for the link, I added few more details. Still unsure where the bighorns come from.
As for the Ilowac-gebirge, I am as skeptical as owls are rather found in Harry Potter. However I found some links to old french books (early 20th) about local geography which mention les "monts des hiboux" (Tawny=Puchac)