Bird Houses & Nests

Every year we had birds using our bird house to lay their eggs and bring their babies into the world.

For some reason they haven't done it this year.

I noticed a lot of insulation inside the bird house and wondered whether this was done by the birds themselves, or by small squirrels that have been with us all winter.

I am going to completely clean it out for next Spring. I will also be keeping a close watch on it after I do until next Spring to be sure it is still clean and empty for the birds to use.

Anybody have any thoughts or suggestions?