These "birdfolk" were introduced in the splatbook "Creature Crucible PC2: Top Ballista", which focuses on the Flying City of Serraine and the various aerial humanoids inclined to live in it. For the most part, they resemble tall (6ft to 6'6") elves, but with large "bird-like" eyes, wing-arms and claw-like feet (like many depictions of a harpy - in fact, ancient Mystaran lore is that harpies were made as a mockery of faenare), and feathery crests on their heads, backs, abdomens and calves.
In fact, the faenare actually believe they are distant relatives of the elves, created by an elven Immortal from the Sphere of Thought. As evidence, they cite the existence of the "wind-haunted", cursed souls who hear strange, beautiful songs incessantly in their mind and which draws them away from their usual insular, clannish society.
Yeah, they got the typical elven xenophobia, but they're not as arrogant as most elves. The flavor text for faenare in Top Ballista has one explain that they are a people of variety, with wits, scallywags and even malcontents, just like the other races of Mystara. Hells, she even admits that they're not a materially focused race, so they don't create lasting physical beauty like dwarves, elves and gnomes. In her own words, they are the people of song, and from this, they find contentment.
They have many powerful magical abilities, mostly because this was Basic D&D and, as elf-kin, the faenare inherited that legacy of internal magic. For starters, they're immune to harpy charms, no "natural" avian creature of any kind, even a roc or a giant bird, will attack them, and they can talk with birds. Furthermore, they're immune to lightning, resistant to air-based attacks, and in a group of at least five, can produce a magical harmony that mimics the effect of a Bless spell. Finally, all faenare are "shamans", which lets them cast clerical or druidic spells.
Oh, and they can fly, but you probably figured that out already.
Faenare windsingers differ from their kinsfolk in that they have access to a number of unique magical songs, which basically function as unique spells. Also, they can reach experience levels normally impossible under the Basic D&D rules, maxing out at level 17 rather than the level 12 cap of the rest of their people.
Connections between the Faenare and the Avariel of the Forgotten Realms remains a matter of speculation.
|Dungeons & Dragons 1st Edition Races|
|Basic Set:||Dwarf - Elf - Hobbit - Human|
|Creature Catalog 1:|| Brownie - Centaur - Dryad - Faun - Hsiao |
Leprechaun - Pixie - Pooka - Redcap - Sidhe
Sprite - Treant - Wood Imp - Wooddrake
|Creature Catalog 2:|| Faenare - Gnome - Gremlin - Harpy |
Nagpa - Pegataur - Sphinx - Tabi
|Creature Catalog 3:||Kna - Kopru - Merrow - Nixie - Triton|
|Dragon Magazine:|| Cayma - Gatorman - Lupin - N'djatwa |
Phanaton - Rakasta - Shazak - Wallara
|Hollow World:|| Beastman - Brute-Man - Hutaakan |
Krugel Orc - Kubbit - Malpheggi Lizard Man
|Known World:|| Bugbear - Goblin - Gnoll |
Hobgoblin - Kobold - Ogre - Troll