Again, I think my 2 are defective. I'll give them a box or a bag and they investigate it but they won't really claim it or spend much time in it - they are getting a bit ancient now mind you, but even when they were younger they only played forts with a cardboard box briefly.
Now my dear departed Radar was an absolute fiend for a good cardboard box or paper bag.
BTW just as an aside, the easiest way to weigh a small bird like a budgie is to pop it in a small paper bag, scrunch up the top, and pop it on the scales