Yesterday, I went to monitor blue bird boxes at a local county park. We checked about seven boxes and found three with nests. One nest belonged to a Carolina Wren. The other belong the a Nuthatch. The eggs of those two birds look exactly the same so you have to identify by the type of nest. Nuthatches have a shallow nest with pinestraw and mulch. The Carolina Wren was much deeper. Our last box contained a blue bird nest with six eggs!
This is a abandoned nest from the Eastern Blue Bird. The blue bird can have 3-7 eggs at a time, though 4-5 is the most common. They can have up to three nests a year. Blue Bird eggs can be light blue or white.
When you are checking a Blue Bird box always come from the side. Knock to let the birds know you are there. It might help if you bring a mirror to see in a deep nest. Watch out because blue birds, will try to dive at you to scare you away.