I have 5 cockatiels. (Started with a bonded pair. Guess what happened.) They all live in a huge cage that was probably meant for larger birds. I've recently discovered that they really, really love paper bags. I'll put one in the bottom of the cage, and they start chattering away to each other about it, and then go down to investigate. The old man of the flock loves playing hide and seek in it. They proceed to chew holes in it over the next few days, until it's time for a new bag.