I was thinking about a fern. Hmmmm, I don't know. Seems like a plant in there would be nice. Most of the lists don't have pictures so I don't even know where to start....How about some shade type impatiens? Jade looks cool and does well in the shade too. In my experience bamboo needs quite a bit of light. Even the so called 'indoor varieties'.
Here's a list of aviary safe plants
Bird Aviary Safe Plants
edit: weird, this one says avoid ficus. I always thought ficus was on the safe list, as it is on Kelli's list..