A week so later, I peeked in and saw some eggs...
Today I noticed a lot of activity going on at the nest, with the birds bringing lots of food in.
Peeking in the nest I saw why... The eggs had hatched.
While I watched the pair brought 3 bugs in under 15 minutes.
Carolina wrens like to nest in odd places like mailboxes and broken taillights, and will nest a couple of times a season. The chicks will fledge in 12-14 days.