Both Protra and NPH are pretty fine grained films and do pretty well up to 16x20, I use NPH for my wedding work and quite often go to 16x20 with no problems, but of course I am dealing with frame filling images of people, so they are designed to be viewed from a certain distance, if shooting birds, you might be pushing the envelope to get some of the smaller birds large enough to see clearly, but you would have to do some experimentation to see what works for you.

Dave