If you have, then here is the answer.
They are placed upside down in small containers and put on a scale. Looks kind of silly doesn't it?
It's just one of the things I learned in the past two weekends while meeting up with and helping out other naturalists who were banding birds. I really learned a lot and appreciated everything. Many birds were banded and data entry was recorded.
Here's a layout of the table and some gear we used.