Harpies and Sirens

Harpies have four distinct limbs plus two wings on their backs, and have avian faces that end in cruel, hooked beaks. Their hands and feet both end in razor sharp talons, and their bodies are covered in feathery fluff.
Sirens look like giant colourful birds, but their faces are human.

Harpies and Sirens are both almost entirely female. The rare few males of either group are enslaved by the females and used as breeding studs. Groups without a male will capture Atlantean men and use them until they get hungry.
Once impregnated, a Harpy or Siren will lay a clutch of eggs in only a few short weeks.

Both of the bird-monsters grow abnormally fast, becoming capable of threatening the Ten Kingdoms only three to four years after hatching. Neither group has an exceptionally long lifespan; Harpies tend to live for twenty years if they aren't killed, while Sirens can live up to fifty to sixty years.

Harpies and Sirens almost exclusively consume intelligent beings for sustenance, something that they only need to do about once every one to three months but are happy to do as often as possible. This mostly consists of offerings from the lesser monsters they rule over, but also extends to Atlanteans that can be captured. They do not attempt to take back the corpses of fallen enemies for food, they only want to eat a being if it is still screaming when they start.
It is common for merchant ships to be attacked by flocks of Harpies, who will attempt to carry off members of the crew for food, while Sirens can take entire vessels. A Siren's voice-curse gains power when travelling over water, and sailors will willingly sail right into the Sirens' clutches once ensnared.

Both kinds of bird-monster has a matriarchal structure centered on either the strongest, or the most magically gifted, female in the flock.
As the only avian monsters, Harpies and Sirens have a distinct advantage over landbound monster species; and they use this advantage to enslave Gnolls, Bugbears, and Trolls whenever they encounter them. These monsters are forced to hunt and build to appease their masters, as well as keep their numbers up so that the birds can eat the weak.

Arrows fletched with feathers from a Siren cannot be blown off their course by Siren magic, normally a major hurdle in hunting the monsters. Feathers only hold this potency for one year after they fall from the Siren.
Centaurs and Satyrs will sometimes make jewelry out of the talons of Harpies that they slay.

Sirens are predominantly found on the coast, and there are many flocks of them hidden on small islands between the Ten Kingdoms.
Harpies live both on the coast, as well as in the mountainous areas of New Atlantis.

Both Harpies and Sirens have exceptional eyesight and hearing.
Sirens posses a powerful magic curse that is channeled through their voice. On land, this takes the form of a sonic attack that can disorient listeners. Over water, the curse magnifies into a hypnotic effect that calls men to jump into the ocean and swim towards the Siren. This power is greater over the ocean or sea, but also applies to the voice travelling over fresh water. They are also capable of hearing the "echo" of other magic users when their voice bounces off of them.

Only the leader of a flock of Harpies is worthy of a name, and naming oneself is the same as challenging her for supremacy. Harpies choose names that they think will inspire fear, either in their flock or their enemies.
Sirens make up a name for themselves when they find the need for one, and a magical aspect of their nature marks them with that name forevermore. Calling themselves by a name that is not their own will strip them of their voice-curse for one week. Their names vary wildly, as each Siren is an individual and could have been influenced by anything.

The largest flock of Harpies in New Atlantis is a pirate outfit that goes by the name "Sharkrender's Wings." They patrol the southern coast of Chivetna, harrying both Azium and Diaspraea and, in recent years, elevating a more than two-thousand year old feud between those Kingdoms.

Harpies and Sirens rarely bother with clothes at all, as they serve no purpose unless heavy enough to be armor and interfere with their flying if they are.

Aven, both varieties, are Harpies' and Sirens' most hated enemies; and are considered the most delicious morsels in the world as a consequence. The consumption of living beings is normally more of a compulsion for bird-monsters; but in the case of Aven it is their true pleasure, and they will often find ways to enhance or extend the torture.