We went to the Penguin encounter, which means we had a private guided tour ($35/person, reservations required). First we visited the kitchen where bird feeding is launched and we spent around 40 minutes in a conference room with a penguin just walking around. Eleven African penguins live in a very nice penguin enclosure, and several of them (maybe all) have a responsibility to meet small groups like ours from time to time. It was fascinating -- the children who were with it were very enthusiastic. These birds are in a sense pets, although they really are reluctant to be stroked, the trainer had to hold the penguin tight so we could see what he felt like.
We also watched the public animal behavior demo, with a large macau flying through a hoop held up by a trainer. Also fascinating. The open bird cages are also quite nice.
I recently spent 6 months in San Diego, where the zoo and wild animal park have much larger bird houses and more birds. However, for its size the Pittsburgh aviary is very good. (The name National does not mean it has any connection with the national government.)