I am an ignorant dork!

Luckily, I keep looking for info to offset my ignorance.

Those were not two halves of one nest. They were two separate nests. And they didn't have "bottoms" cuz they attach like cradles against a vertical wall. They are the nest of Chimney Swifts and I obviously have a family nesting in my chimney. The mucilage on the corners of the nest is what attaches them to the wall. Here's are the nests. (I put the remaining egg in one of them to demonstrate what it would look like.)







Here's a close up.

I've seen the little guys flying into the chimney, but they are hard to photograph cuz they don't stop or light first. They just fly right in.

Here's a link to a swift webcam in Driftwood TX, (not far from my Central Austin home):

http://www.chimneyswifts.org/page2.html