Thanks, everybody, and keep commenting if you have more to say. I am now paying more attention to what I do. This is what happens: I always learn songs orally either from recordings or from singers I meet. The form of Scots my songs take depends on which singer I've heard. Once I've heard multiple versions I will often sing whatever sings easiest for me. This means I will unconsciously start converting some sounds from Scots to English here and there -- sometimes "tae" becomes "to" -- and sometimes not -- it depends on the phrasing of the song. For example, in "Bonnie Susie Clelland" I sing "wha dearly lo'es me" in the refrains, but I might sing "The father" instead of "The feither." Probably over time the drift is toward American English, but I never change vocabulary and never change things deliberately.