I just adore bird's nests...
They are pretty, delicate, intricate and crafted with love I'm sure. And I can't help but think what fabulous centerpieces they would make! Of course, I would use only abandoned bird nests...but placed on a pretty plate or a cake plate they would be quite stunning.
For a more natural rustic centerpiece idea I would place them on wood rounds, a mossy branch or the table itself. If the idea of hunting down a lot of empty nests seems like a big task (which it can be), how about using just one or two at your reception. It would be such a pretty little detail!
...photography craig wall