Mice
Could be them too.
I had a bat living in the kitchen ceiling. In the cavity of an old flouresent light that had been covered up. I removed the light to fill in the ceiling and left the hole open overnight.
The bat came in between the siding and the vent for the range exhaust vent.
I came down the next morning and it was hanging out in the family room. Literally hanging off the wall of the bookcase.
Just chillin