Well, thanks everyone. I've heard Duke singing enough in movies to get the impression that carrying a tune wasn't one of his strengths. And the whistling in that song was at least as good as anything I've ever heard even Bing Crosby do, so...
I don't really know which movie has my favorite music. I do love the love theme from The Quiet Man, of course - the "Isle of Inisfree." Very, very pretty.
I also really like the theme from The High and the Mighty. I've never seen the film, but it's one my dad's told me about before. He hasn't seen it since he was a kid and he wishes they would show it again on TV or release it for home video. I understand that it's tied up in legal battles and the like but maybe someday.
Anyway, does Duke actually do the whistling? That's some mighty pretty whistling!