Well, there is a way. Actually a couple of ways.
First thing you can do is to pump up the frequency range of the whistle part and to reduce the frequency range of the rest of the mix using an equalizer. This can be accomplished with either software or hardware. Do you have Audacity by any chance? There are a few EQ plug-ins that you can use with Audacity that should do the trick. EQ is covered in the Audacity manual if I recall correctly. Just look up the high and low frequencies of the whistle he is using (was that one low D?) and use those figures to set your floor and ceiling thresholds. You can play with the levels to see if you can isolate his playing. Problem is that if their is any other material in the same frequency range it will be brought out equally.
The second way I can think of involves a piece of software that is designed to isolate parts in a recording for sampling. There is likely some freeware out there for this. I just don't keep up with such things. These things work like Karaoke filters in reverse to filter everything but the lead voice or instrument out of the sample. That usually involves analyzing the stereo image and using wave cancelling to filter the parts. Roland makes a piece of software called R-Mix That will do what you need. It's a $200 package but also comes as an add-on to Cakewalk Sonar X2 Producer, maybe others. It is darned amazing. It can isolate just about any part of a recording.
Take a look at this YouTube overview.Once you isolate the part you save it as a a recording clip. Then you try to either analyze the melody by ear or use the usual pitch analysis tools (like Transcribe)to identify the notes. You could also play it through a pitch to midi filter to identify the notes. That's probably more than you'd want to get into.
Might be easier if one of us here gives it a go by ear.
Feadoggie