I learned to yodel a bit because I needed something to "tear the house down" with, a show stopper. Cathy Fink and Todd Whatshisname had a two tape series on Homespun Tapes "Learn To Yodel" I'd recommend it. Takes you from that Cajun "ayee" to the Jimmie Rodgers blue yodel, to some pretty fancy-schmancy cowboy yodeling. Bill Staines makes a brief presentation where he breaks down his yodel breaks to "The Happy Yodel Song" and "Ballad of the Maples"