nesting box (for garden birds)

Thank you to Kdor for the nice design.

Now this is a nesting box for garden birds.

I design it in two versions. To hang it in the tree (not sure whether this is a good idea - make sure the wind can not move it to much) or to mount it on the wall (with a screw on the backside). It's my first nesting box so I read this german text for the dimensions and the holes https://www.berlin.de/special/haustiere/4296503-2840263-nistkasten-selber-bauen-lochgroesse-ist-.html I guess this is a usable res