vealbunny said:
I think harpies probably do parthenogenesis, being an all-female species. Or maybe the "human female" appearance is just mimicry, and they actually have male and female sexes with very little distinction between sexes. Mermaids could have more potential for variety based on the species of fish they come from.
According to author Piers Anthony, there ARE male harpies but they're extremely rare, with only a handful born per generation. Female harpies are extremely protective of the males because of their rarity, and never allow them to leave the safety of the main harpy roost. In the absence of a male harpy, to reproduce female harpies must mate with male humans and male vultures in alternating generations.
The book that goes into this in detail is
Castle Roogna, the third book in the
Xanth series.