We noticed a lot of activity going on around the jar about 6 weeks ago, and at first we just thought birds were getting leaves and stuff out of the jar to build a nest somewhere. But when I peeked in, I was surprised to see that they were actually building a nest IN the jar! We discreetly checked every few days until there were five little speckled eggs in the nest. We went out of town for two weeks, and came home just days before the hatching. It's been so fun to peek in and see them growing!
My only wonder is... how will the babies get out of the jar?! I guess we'll find out soon!
(Oh, and from the eggs and watching mom and dad bird, we were able to identify them as House Wrens!)