Bird mounts

Bird mounts are mounts, that are obtained from a variety of different ways.

Achievement

 * Corrupted Egg of Millagazor is rewarded from Glory of the Firelands Raider.
 * Felfire Hawk is rewarded from Mountacular.
 * Frenzied Feltalon is rewarded from A Horde of Hoofbeats.

Drops

 * Reins of the Raven Lord is a rare drop from Anzu in heroic Sethekk Halls.
 * Flametalon of Alysrazor is a rare drop from Alysrazor in the Firelands.
 * Smoldering Egg of Millagazor is a rare drop from Ragnaros in the Firelands.
 * Voidtalon of the Dark Star is contained in the object "Voidtalon Egg". The egg is found from stepping into an Edge of Reality, which rarely spawns all around.
 * Clutch of Ji-Kun is a rare drop from Ji-Kun in Throne of Thunder.
 * Sharkbait's Favorite Crackers is a rare drop from Harlan Sweete in Freehold on mythic difficulty, or from the Mythic Plus Challenger's Cache.
 * Squawks can drop from any difficulty of Island Expeditions.
 * Waste Marauder
 * Clutch of Ha-Li
 * Reins of the Colossal Slaughterclaw drops from Supplies of the Undying Army.
 * Slime-Covered Reins of the Hulking Deathroc drops from Violet Mistake.
 * Predatory Plagueroc drops from Gieger.

Quest

 * Shadowblade's Murderous Omen is a Rogue-only quest reward from Hiding In Plain Sight.
 * Kirin Tor Summoning Crystal, which teaches you how to summon the Violet Spellwing, is a reward from Blood of a Titan (quest)

Vendor

 * Reins of the Corrupted Dreadwing is purchased from in Tanaan Jungle at a cost of  upon reaching  with Order of the Awakened.
 * Mephitic Reins of Dark Portent, Bloody Reins of Dark Portent and Midnight Black Reins of Dark Portent can be bought once Power Ascended is achieved for Assassination, Outlaw and Subtlety specializations respectively. Zan Shivsproket sells them in the Hall of Shadows for each once the quest mount is obtained.
 * Siltwing Albatross is bought for from vendors in Boralus and Zuldazar.
 * Wastewander Skyterror

Abominable Stitching

 * Bonesewn Fleshroc

Collector's Edition

 * Reins of the Dread Raven is a flying mount included in the World of Warcraft: Warlords of Draenor Collector's Edition, or can be bought as part of a bundle from the Blizzard Store.

Trading Card Game

 * Magic Rooster Egg is gained by using a code from a specific card from the World of Warcraft Trading Card Game.

Stormcrow
The Stormcrow (mount) is a bird mount that was datamined from the game during Mists of Pandaria. It has never been implemented, but does have a miniature version that is available as a companion pet.

Druid Travel Form
Druid Travel Form functions the same as a mount, and most of the flight forms are birds, excluding the Troll and Zandalari troll who have a bat and pterrordax form respectively.