So when I was shopping for my whistle I knew I wanted a Low D, but I have to admit I was confused about some of the terminology of the others. They were labeled mezzo, alto, soprano, and don’t forget High D. So it got me thinking. Where these fall in relation to middle c? Also how many octaves separate a Low and high whistle? Is D they highest key made (excluding obscure whistles)? There has to be a beginners guide somewhere. I know I could answer some of these questions if I had my whistle, but it’s taking a vacation @ US customs. 
I guess I’m stuck with you guys to entertain me. 
Generation makes mass market whistles in Eb, F, and G above soprano D, and no doubt some craftsmen makers will have similar or slightly different models. High G is really shrill and the holes are really close together, so if you’re an adult you’ll find it difficult. I don’t speak piano so I might have this wrong, but my impression is that the lowest note on a high D whistle is a ninth above middle C (a whole tone plus an octave), and that a low whistle in D is a whole tone above middle C. I’d use high D and soprano D interchangeably. You see terms like mezzo or alto used for keys like A & G, where you can have a whistle that’s only a few notes lower than a standard C or D whistle. I don’t think there’s an official definition.
That clears things up. Thanks!
As a further point, I’ll say that conventional whistle notation renders the notes an octave lower than they’d actually appear on a piano keyboard or ‘grand staff’ notation. It’s easier to read that way.
It’d be accurate for a low whistle, but all the conventions for notating whistle music were created before the invention of low whistles. To be exquisitely accurate it should have the ‘octavo’ symbol applied above the staff, but no one does that.
They make some high whistles that will drive dogs crazy 100’s of yards away from you! Bigly fun times doing that to dogs!