When in doubt about the origins of a monster, blame it on an aelf. In this case, evidence of the existence of harpies is well-attested back into the 2nd age. And their structure matches fairly well with what you'd get if a Twisted-worshipping aelf biomancer with a particularly...odd...fetish took a goblin and a vulture and merged the two. --The Immortal Bard, Bestiaries of Legend You're a fine one to talk about elves and fetishes...although yours are more "is female and doesn't run away." -- Dovara Brightsong, head of the Bardic College at Kaelthia and descendent of the Bard himself.
Harpies are a rare species of monstrosity known to inhabit many of the waste and fringe lands of Noefra and other continents. They are roughly a cross between a goblinoid torso, arms/hands (although clawed) and upper legs and head and a vulture's wings and lower legs/claws. The males of the species (rarer than the females) have raptorial beaks as well; the females have fully goblinoid heads but sharpened carnivore teeth. Both sexes have aggressively exaggerated secondary sexual characteristics and external genitalia. They are obligate carnivores, although like dogs they can eat small amounts of grains and other vegetable matter.
Standing between 3'6" and 4' tall, with 6-8' wingspans, they are clumsy fliers and not particularly adept on land. As for intelligence, they are human-level with a particular aptitude for languages. Their carnivorous bent and dangerous song makes them outcasts in the civilized societies of the Federated Nations. While not kill-on-sight like undead, they are not welcome. As such, they gather in small flocks in uninhabited or tribal lands (especially along the southern reaches of the Windwalker Confederacy) where they can hunt small creatures. Many have gone full on into the worship of various malign powers including demons. These groups particularly like to prey on the small-folk, including goblins that they can lure over cliffs.
Temperamentally, they are generally cowardly but aggressive, with strong and often violent tempers. Finding clothes that fit them is difficult, and their lack of good manipulating members make them clumsy with tools. So they rarely bother with clothing or more than rudimentary weapons, relying on their claws, teeth, and (in the case of the females), their song. Their diet of meat (fresh or not) and lack of manipulators makes them often foul-smelling and covered in blood and other rancid matter, and their nests are frequently befouled as well with their own droppings. The males lack the musical capabilities and are less facile with spoken languages (due to their beak-like faces) and are often more aggressive than the females.
These properties are not inherent, however--there are a few legends of "well-kept" harpies who use their song for good and keep themselves clean and presentable. Those are not substantiated, however. Harpies are not known for magical or religious properties.
Female harpies are born with the capacity to produce a bewitching magical song; those that cannot resist its pull are forced to walk ever closer until the harpy eviscerates them and begins feasting while the prey is still alive. They can tune the song to lure humanoid creatures or beasts, but not both with the same song.
Harpies nest in groups of 2-3 females and 1-2 males, producing several eggs each year in late winter/early spring. These eggs are large, roughly the size of an ostrich egg, and hatch over the course of roughly 6 weeks. The child is born small and weak, with fuzzy feathers all over their backs. They have sharp teeth/beaks from birth as well as claws and talons. They mature rapidly, reaching adulthood within two years, at which most flocks kick them out. Casualties among the fledglings are quite high in the wild, with 1-2 out of 10 eggs producing adults. They pick up languages very fast--within the first two months they have learned to speak as well as whoever is raising them. They are voracious, eating their weight in fresh (or slightly decaying, they don't really care generally) meat every day.
Harpies live between 15 and 20 years if not killed much sooner by violence, starvation, or other causes. Most do not live beyond 5-10 years.