I have only hunted elk the last 10 years but my experience runs along with what flags said. There seems to be no rhyme or reason to elk bugling. I look at them much the way as turkey. Gobbling or bugling like crazy one day and then nothing and they are still there. In both instances pressure can accomplish that or if the animal through the situation isn't looking for something to breed. Both sound off to protect territory and IMO that is the part most easily quieted. I am a lifelong turkey hunter and found hunting elk to be similar with the calling. Too much or too little and you blow it.