Birbs…..birbs...BIRBS! Lol. I love them, you love them, we all do! ÚwÙ They be fluffy! But, before we start, first off, how are you today? And secondly the characters in this picture are aged up to my current NG time.
Anyways, this is sort of a continuation of pony races and what I have head cannoned for them. HOWEVER, hopefully it won't be as long as the Unicorns. And also, I'm not necessarily gonna do one on Earth ponies, not because I don't like them or they're boring or anything (they're GREAT). It's just that Lopoddity has a better HC for them and it would almost seem like copying if I did my own HC of them, lol. So, here's the link to her HC!:
https://www.deviantart.com/lopoddity/art/Notes-on-Equus-Terra-814888161

I absolutely find her HC to be very interesting and frankly, logical for the biology of these mythical creatures within the magical land of Equestria. And if you know me, I enjoy things that creatively make sense, lol XP. So sorry in advance for using a million of her ideas, but also not sorry because she deserves the phrase for her creativity! ÙwÚ

Alright, to clarify, I'm fully aware that hippogriffs aren't pegasus, and vice versa. I honestly feel like the two races shared a common ancestor that the two evolved from; I'ma call them Avequus for now (a mixture of aves for bird and equus for horse). More than likely, the avequus had a civil war or had a group travel westward and ended up in pony ground. The ancestors that traveled west ended up becoming the pegasus we know and love. The ancestors that stayed behind remained the race they already were (with a few evolutionary changes).

COMMON PEGASUS/HIPPOGRIFF FACTS:
Usually have muzzle markings that resemble bird beaks, markings around the eyes and a lighter underbelly. Their hair is commonly short or put up to prevent accidents or to keep out of their face (usually rocking mohawks, bobs, bowl cuts and pixie cuts). First to bear the most kin out of the pony kind. Baby pegasus are called chicks, Female pegasus are called hens, and well males are called cocks…..or drakes. I'm just gonna go with drake because I'm immature XP. Their color schemes usually consist of blues, whites, and yellows, but they can come in any color. Their names also are associated with aerial or sporty meanings. The dominant mate in a relationship will make a nest for their love, to show that they care and will sacrifice time and resources for them; to show commitment. So basically nests are like engagement rings in the pegasus and hippogriff society.
Naturally, pegasus have magic in them that allows them to fly. That can explain how Bulk Biceps can fly (but most of y'all already knew that). Most famous singers are pegasus or hippogriffs for their given vocal dynamics.

HIPPOGRIFFS: Princess Skystar here is your example for a normal typical modern hippogriff. (Another inspiration from Lop) they're usually rocking tropical color schemes and perky attitudes. Like what Lop also HC in this AMAZING picture:
https://www.deviantart.com/lopoddity/art/HC-Birbs-784793393
Hippogriffs wouldn't be gloomy, mean, dole and predatory beast like griffins, and I also agree that hippogriffs are quite literally the tropical version of a griffin. Hippogriffs are very tropical island or beach line driven and'll reside amongst them, because those are the perfect ecosystems to live in for them. If this were the real world, places like South America, Hawaii, and New Zealand are where you might find them.
They are naturally the second biggest bird-like species with the biggest wingspan (behind feathered dragons XP). And I say naturally because you have ponies like Celestia that are HUGE, but Celestia isn't natural, she's beautifully artificial ÚwÙ 👌. Like any other bird, they have the most angelic singing voice (of course besides the Sirens for reasons) and are the most striking in appearance (like I explained before). They have the most chicks out of all of them all (or I suppose out of the bird pony types species) AND since they too can turn into merponies, the males are the ones giving birth (another inspiration from LOPODDITY ÓwÒ:
https://www.deviantart.com/lopoddity/art/Quarantine-Doodles-834668924

ANCIENT PEGASUS: As you may know, Flash Magnus is a Pillar, and the Pillars are OLD. But due to that limbo state, it was able to truly preserve ancient history. Flash almost appears to be a mixture in between a pegasus and a hippogriff, with those long feathery ears, a beak-like muzzle, bigger sturdier body, and different front legs (it's the hooves. Coming from talons to hooves, this is what I could've imagined it looked like). He (and the ancient pegasus) almost seemed like the missing link for avequus evolving into pegasus.
But anyways, these ancient pegasus were Greek militia inspired, and were (at the time) stronger and bigger than most pony kinds. By the way, they have become entirely extinct (except for Magnus… for now 👀)

MINIATURE PEGASUS: Sure you could say midgets but there's so many of them in Cloudsdale we may as well deem them as their own thing XP. I randomly used Short Fuse as my example for a miniature pegasus, however other examples in my AU include, Rainbow Dash and Luna. The only other thing about them is that they're feistier and more daring to prove their worthiness (and also because everypony and beyond belittles them). However, these little ponies can fly WAY faster since they're much lighter as their wingspan is much longer than them. And since they're so small and light, like how RD was able to do, they can sleep or chill out on trees without breaking the branches.

MIXED PEGASUS: They are 50% pegasus and 50% whatever. Sometimes they lack the abilities to fly, like Scootaloo (or Scooter in my headcanon. I hc Scootaloo as trans), or the interest in it (like Cozy; she's a pegasus and a unicorn). As we may know, Scooter is mixed with an earth pony and a pegasus. Genetically speaking, since both of his parents are tall and bulky (well his father), Scooter was gonna have a body that would be bigger than his wings (like Bulk Biceps). And since I feel like Scooter possesses more earth pony than pegasus, the magical balance there isn't looking all too good. So this results in Scooter not being able to fly.

Now Cozy, she's not too fond of flight, because she does most of her work on land. End of story. XP Btw, if any hornless species is mixed with a unicorn, I'd feel like they would have this star or diamond like marking on their forehead to indicate where a horn should be. Also, VERY rarely a True Alicorn can be born from pegasus and unicorn parents.

ANYWAYS, that's all I have for now y'all. And again, THANK Y'ALL FOR YOUR CONSTANT SUPPORT!! I LOVE Y'ALL! ^{w^}

If you have any questions or whatnot, leave a comment down below! ^{^}

(P.S. I wonder if you can spot a Squid Game reference in this pic 👀)