Spotting

I also think birch poypore because there are not many bracket mushrooms that have a kidney shape. They tend to grow in singles. If it were something like oyster mushrooms, you would have a bunch of them growing together.

http://greennature.com/shelf-mushrooms.h...

Ill upload a pic of the underside too~ I thought I did before. It's very smooth underneath

Might be Birch Polypore (Piptoporus betulinus) as it looks about right and it is on a birch tree, but it is hard to make fungi IDs without photos of the underside