One thing I simultaneously love and hate about D&D, in all its forms, is the proliferation of races within a confined setting.
Each Monster Manual has dozens of sentient races, and back in the 3rd Edition days, most of these had opportunities to use as player characters. While I understand that these are for a more "toolbox" approach, settings like the Forgotten Realms tried to use everything - and what you were left with was three or four races that filled the exact same niche, whether it was story-based or ecologically - for every niche.
In terms of story, there are approximately a billion different first-level threats to choose from - but for most GMs, it comes down to Goblins, Kobolds, or some kind of low-level Undead.
I wanted something a bit different, so I decided to take a look at Kenku - bird-like humanoids, resembling crows/ravens with no wings and a human-like stance. Their culture is pretty weakly defined - they're born in nests, live near large cities, are sneaky and secretive, and make good Rogues/Assassins.
That's about it.
So, here's an attempt to flesh them out a little, and make them a good fit for a new setting.
Above all things, Kenku hold secrets to be most important - after all, Knowledge is Power, and what holds more power than a well-kept secret? Most worship a minor God of Secrets and Lies - Crow/Raven (occasionally referred to as The Corvus, The Dark Bird, or The Great Bird, mainly by it's Clerics), a two-faced god, with Crow representing Secrecy, Knowledge and Magic, and Raven representing Darkness, Death and Stealth. There are many, many supposed creation myths attributed to the Kenku and Crow/Raven - whether they were brothers who simultaneously ascended to divinity, entagling their divine essence with one another, or The First Bird, which flew itself to Heaven and took a place protecting all its kindred. Some even claim that The Corvus was once the pet of a now dead God, who took his essence and took over His portfolio. Only one thing's certain - if it was a Kenku who told you the tale, chances are they are lying. The true secret of their origins (if indeed it can be said to exist) is "The Secret" for Kenku - the other tales are lies and misdirection, either to protect the true knowledge, or just as a practical joke on those who might ask.
Due to their desire for intrigue, many take up home in or around larger settlements of intelligent Humanoids, and attempt to work their way into the political scene - either directly (in more tolerant areas), through underground criminal rings, or through patsies and representatives. Due to the knowledge they hoard, many high-ranking Kenku have other humanoids over a barrel, with little choice but to be their stand-ins in the games of politics for fear of what secrets might be released. Many learn several languages, including "dead" ones, and their natural ability to mimic the voices of others feeds directly into that - no point in pretending to be a Gnoll when you don't speak either Gnoll or Abyssal, right?
Kenku live in family units (referred to as clutches), with several family units (normally extended families, those related by blood, etc.) forming a Murder. Most Murders are fairly close-knit, and form an extended family. When large numbers of Kenku are present, several Murders may come together to form a Flock, a loose association of families and aquaintences. Flocks can occasionally include non-Kenku families, mainly those who have a member who has done the Flock (or a particularly high-ranking Murder) some great kindness.
Kenku take several names and aliases, in part due to their obsession with secrets - their real names are often obscured amongst a web of nicknames, false identities and adopted titles. This makes them pretty hard to track, both via magic and through more mundane means. These names are taken from deeds (Slasher, Goblin-Killer), characteristics (Red-Eye, Strongarm) or even just cribbed wholesale from other races.
Kenku are most commonly seen associating with their own kind, but seem to have a special place within their society for Kobolds - possibly, the Kobold's natural talent for stealth and trickerey appeals to the Kenku, and their downtrodden underclass status makes them perfect spies. They also share a common desire for knowledge, specifically in the arcane for Kobolds - but to a Kenku, all knowledge is useful, and Kobolds seem pretty willing to share that knowledge with them. They have no real emnity with other races, but their secretive nature makes them far less likely to socialise outside their own kind than most races.
Kenku stand roughly 4'6"-5'6", with very few being taller (but a fair number being smaller). Being descended from birds, their bone structure is partly hollow - making them both lighter and somewhat less resiliant than other races.
Kenku mostly take up adventuring for the simple reason of finding lost tomes of information, old maps, journals - whatever bits of information they can scavenge. Some go to find the secrets of the universe - many following this path end up out on the Planes, and Sigil's got a healthy population of them (mostly in the Hive Ward, though a few have worked their families up to prime Lady's Ward homes). Some have a specific piece of information in mind, and some just wait and see what comes to them.
Many follow the path of the Thief and Sneak - Rogues, Assassins, and Bards are all very common amongst Kenku. Some follow the path of magic, with Wizards being most common (despite worshipping a God of Magic, Kenku are no more inclined to Sorcery than other races) - their lust for arcane power only tempered by their drive for secret rituals and knowledge. Fighters and plain warriors are uncommon - most who do become swordsmen are more likely to use their heads and think their way out of a fight than actually battle.
See - easy. You can keep the same stats and abilities for 3.5/4e, though I might recommend swapping one of their bonuses of an Int boost.