Gallery,  page 16
Here's a curiousity.  We accidentally left a couple of four inch vent tubes (these will feed outside
air to the fireplace) uncapped.  Some Rock Wrens, as shown on below in a picture I stole from an
Audubon Society website, made nests in each of them.  The nests were just twigs and stuff, but it
turns out these particular birds make a walkway of small stones at the entrance to their nests.  
No one has figured out why, supposedly.  I took the bottom picture looking into one of the tubes.  
Each pebble is almost the size of a quarter, so these little birds had to work to get them up there.
 The birds squawked and scolded us a bit if we got too close to the tubes, but otherwise pretty
much ignored us and often perched within a few feet of us while we worked.