Think of a case where there is a treadmill mounted vertically inside the container with perches attached at intervals so the bird can step from one to the other in such a way that it stays in the same position relative to the conveyor apparatus and the container. The weight-force of the bird will be transferred through the conveyor apparatus to the container, just as it would be transferred through the air to the container, and with the same effect as though it was sitting on a stationary perch.

Sorry, I just had to do it.[sm=bananahead.gif]

Don't kill me.

By the way, I love the Swallow Dialogue from Monty Python. I'm glad someone got my hint.