Some sources claim that the Dayak fruit bat, Lesser short-nosed fruit bat, and Bismarck masked flying fox (flying fox is another name for fruit bat actually) have males lactate milk. How did the males of this species gain this ability and what do they use it for?
The Wikipedia article says they might assist in nursing…
My only guess would be is that the lactating assists mothers with nursing the young, otherwise I would have no clue. It’s a very interesting fact.