I was at the San Diego Wild Animal Park a few days ago on a "photo safari." One of the other people there was a professional wild life photographer (but I didn't get his name). He had a beauty of a lens.....wide to super tele (17 to 400? 28 to 400? something, and on a Nikon), but he told me he shot the whole thing on 5.6. I was surprised and thought a smaller aperture would have been used.
I opened up from 9 to to 5.6. I'm not thrilled with all the results, but that's due to reasons other than the aperture.