Oops, forgot to get back to this thread - sorry!
I tested the eggcup theory (with an unbroken egg, luckily), and it was slipping and sliding all over the place. So I suspect napkin-holder, which is a shame as bird-shaped glass eggcups would be terribly fun to have on the breakfast table!
The birds are 75mm tall, 20mm deep at the thickest part (they're slightly wedge-shaped), and the hole has a diameter of 30mm.