Cow calling has always worked way better for me than bugling. You can have elk all around you with them not making a sound, but they are there. Even when you call, they may not call back but they may be responding silently. Once a bull let out a short bugle from several hundred yards away immediately after I cow called and he arrived on the scene within two minutes with his nose working like a hound dog. A nice medium six point. I had a cow tag. Arrgh!
Bugling at a herd bull while you move toward him will almost always send him and his cows away from you. If you are going to bugle as you move toward a bull that is answering, try to sound like a very small non-threatening adversary.
Sometimes you can call back and forth with a bull for a long time and if you stay put they stay put. So, if you have a partner, one stays put and keeps him talking while the other moves in. Not easy getting close to a herd of eyes, ears and noses though!
I treat using a cow call like it is a predator hunt. Set up and whine for at least 30 minutes or more and then relocate. Always assume that there is a bull in earshot and he is coming in. Partnering is very effective because the shooter can be set up at a different location. The bull knows exactly where the caller is!!
A lot of the guys I hear using a cow call are blowing it all wrong. Many of them blow with a sharp series of closely spaced and rather harsh mews and chirps. IMO, those calls are just a small mistake away from being a warning call. A cow in heat does not make the same call as the cows and calves as they "chat" amongst themselves. "Chat" is occasional low chirps with no sense of urgency to them. If you are moving through the woods and you make some noise, a few correct chirps will settle the elk down if they have heard you and are unsettled by the sounds.
My standard hot cow call is a series of three mews about two seconds long and spaced about two seconds apart. That and the predator technique has accounted for all but a few elk I've called.
Also, don't get me wrong, I AM NOT AN EXPERT WITH ENDLESS SUCCESSES TO MY CREDIT! I'm just a regular run of the mill hunter passing on what has worked for me over the years.