One of the most common birds that will use nesting boxes is the Chickadees. From my research it appears that the Black Capped Chickadees is more likely to use a nesting box as opposed to the smaller Carolina Chickadee. I have both of these characters in my garden and I have been fortunate to attract a Black Capped to a nesting box I placed under some pretty large pines. Last year I had a Chickadee build a nest but a critter killed one of them. This year I put a homemade squirrel guard on the box entrance and that seems to have done the trick.
Generally they have 5-10 eggs and at last count my box had 9 eggs. I snapped this pic really quickly and I didn't bother checking to see if the count had gone above 9 - the way I see it these little guys are going to be VERY busy this spring. I have 2 kids and I couldn't imagine having to look after another 7 of them..... BTW, as you can see the eggs are pretty small, white with brown speckles.
The lady of the house was waiting eagerly to return to brooding so I quickly closed up the box and moved off.
For detailed info about these amazingly cute bundles of joy check out Whatbird.com