This is not part of any Islamic tradition that I'm aware of.
So why don't Muslim clerics CONDEMN it? Can't they excommunicate (or whatever they call it) any African Muslim who condones this practice?
Because their is no central religious authority in Islam (like the Papacy). (the first Arab Imperial state killed off virtually all of Mohammed's descendants)
Also, because in Africa-- the clerics are African themselves and probably seek to preserve the animist culture the were raised into.