Chiru, or Tibetan antelope have arrived for the winter rut. In the energy-sapping thin air , the males must try to control groups of females by constantly rounding them up and corralling them. But the chiru have an advantage. Their red blood cell count is twice as high as ours , sufficient to supply their muscles with oxygen, even at this extreme altitude. Nevertheless,it's hard work keeping his harem in check, and the male's life is about to get even harder. Another male is gearing up to steal his females. With their rapier-like horns,the males won't risk fighting unless they really have to. But if neither backs down, conflict is inevitable. Some of these fights end in death.