From the first days of September the mountain valleys start to echo. Bull elk are in rut, and the bugle is how a bull advertises himself: a low bellow that climbs into a thin, carrying whistle and then falls away into a run of grunts. It is an odd sound to come out of a 300 kg animal, and the reason is that he is making two sounds at once. Researchers who recorded wapiti bugles found two independent sound sources inside a single call, a low roar near 145 Hz and a whistle above 1400 Hz, and suggested the low part advertises his size to rivals nearby while the high part carries his presence down the length of the valley. Bugling peaks through late September and is mostly finished by the middle of October.