I tried with cooked bone, that tends to be what I have more of lying around :D
I don't recall the voltage I tried, but it was probably something in the range of 5-9v. I didn't try with a very thin slice, it was a few mm thick. Probably a thinner slice is the thing to try. That's a bit hard with bird bones (hollow), so maybe I'll have to cook something else. I don't have a microtome, so I'll have to cut some thin slices by trial and error.
I would hazard a bet that orientation matters. The studies that measured bone piezoelectricity seemed to suggest some orientations made more sense than others, but I don't recall what exactly. In any case, they had... very different applications in mind.