Bone doesn't rotate at right axis I created an armature for my birds wing. The wing should be exactly rotated from the edge of the part of the wing. But everytime I rotate it by the x axis it leaves this line and there is some space between it (see the picture). This is because the part of the wing isn't parallel to the ground, but it goes up a bit in the Z axis. I don't know what to do, to tell the bone to rotate by another custom axis...

My .blend file:
You have three options,

1) what you want is to rotate bone on custom axis, for this please see 
Rotate object on axis between two points

2) if (1) this is cumbersome then i'll suggest, join all mesh (KFlügelR, FlügelL, Vogel, FlügelL, KFlügelL) together (select all mesh and do ctrl+j ). Then assign the armature to this joined mesh, use auto weight for first try . ( if you do not know how to do this then just ask :) )

3) Make the mesh so that its pivot is aligned to the bone orientation.

I'll suggest option (2), as it should be the right way anyhow.