An idea which I always think of but have never tried. . .
We've had a copy of the Peterson's North American Birds interactive CD ROM on our computer for years and like it a lot. It gives you all of the text, drawings and maps from the Peterson Guides, in addition to striking photographs and well-recorded calls for all of the species. We do not own a notebook computer. If we had one, and it wasn't too bulky or obtrusive, I think that the CD ROM would make an excellent field guide to carry with you. It is very easy to navigate within the program and, if there were halfway decent speakers or an earphone jack on the notebook computer, would be a good way to carry the calls you need in an easily retrievable format.
Just a thought.
Larry and Mona