One Nest Box, Three Species Reared in One Season

I cleaned out the yard nest box today.  I finally was able to the see the layer cake of nests that were built within it that as far as I know successfully produced three families of birds, each of a different species between February and early July

Here is a side view of the nests.  On the bottom, constructed of mostly tree mosses, is that of Carolina Chickadee, just above that is a thin band of grasses etc. which represent the nest of hybrid Tufted Titmouse (this will appear better in the last photo) and finally the trashy nest of Carolina Wrens which filled the box.

Here a view of the Carolina Wren nest with an egg that never hatched...note the snake skin portions

  All three nests shown as layers...This nest box always produced a lot of birds...But only this one...Two others I have rarely have nests.  It has to be a matter of location.