Practice makeing the tone and cadence. I force air up from my diaphragm versus just "exhaling" I also, try to get the echo sound by letting my cheeks expand.
As far as voice yelping, I may not be the best, but I have called in and killed turkeys by doing it. I tighten my throat to get the higher pitch and somehow I get a little rasp, too. Maybe I should record my voice calling so you get the jist.