It is thought to have spread from Nepal around the inhospitable Tibetan Plateau, to rejoin in Siberia, where the plumbeitarsus and the viridanus appeared to no longer mutually reproduce.
Den formodes at have spredt sig fra Nepal rundt om det ugæstfrie Tibetanske Plateau for at genforenes i Siberien, hvor underarterne plumbeitarsus og viridanus synes ikke længere at være i stand til at parre sig.