Bird Nest

Bluebird house number 1! Pretty sure this is not a bluebird nest. Lol. I was surprised when I opened my birdhouse to find this packed nest. It reminds me more a gerbil nest! Lol. Any idea who built it? There were no eggs, but there is a small red feather in the side there (you can see it in the picture.) I don't think House Finches build like this (the males have red feathers as such.)