This is a vanilla mob creation. It adds birds that randomly spawn around players that come in red or brown variants as well as baby and adult. They can fly, walk around, be fed, grow into adults, make nests, and drop items that can be used to custom craft some items! No resource packs or mods are used and it works completely in vanilla 1.8.

(Note: This was made for Minecraft version 1.8, not yet tested with multiplayer but should work)

[ Reddit Post ]

I would suggest using the following gamerules when using the schematic:
/gamerule commandBlockOut false
/gamerule logAdminCommands false

UPDATE 1: Fixed a little screw up with the randomizer. I forgot to remove some testing blocks that stop them from making nests and spawning naturally! Sorry about that!

UPDATE 2: Continuing the first update, fixed bird flying.

UPDATE 3: Improved glitch where birds close to each other glitch into each other. Do not spawn birds closer than 3 blocks near each other or force them together.

UPDATE 4: Improved glitch more where birds close to each other glitch into each other. Bird model resets after glitching. (Thanks MC Labs15!)

UPDATE 5: Hid annoying scoreboard left on screen when loading world download.

UPDATE 6: Fixed bird head displaying as Steve.

WARNING: Don't spawn birds directly next to each other or force them together! When they come near each other they glitch really badly :P! If they are above 3 blocks apart they will be ok.

Features:

Birds
- Randomly spawn around a player
- Fly through air, walk on ground, hop occasionally, and make sounds!
- Red, Brown, Baby, and Adult varieties of birds
- Can be fed by dropping wheat seeds on them
- Drop Odd Bird Egg when fed as an adult which breaks when dropped from heights to get Yolk, Egg White, and Egg Shell
- Create nests rarely when adult and on a leaf block
- Nests spawn 3 baby birds over time, then break into sticks
- Rarely drop Bird Wing when killed
- Killed by arrows only
- Animated wings

Crafting
- Crafting Machine for custom recipes (may expand on this in the future in a different post)
- Two recipes for Omelette and Winged Armor
- Omelettes provide +2 max health when held in hand and can be eaten
- Winged Armor when worn gives speed, jump boost, and feather falling IV

Flying Machine
- Created when placing Winged Armor on armor stand with leather cap
- Can be ridden and flown in any direction you look!
- Animated wings

Guide Book (Not Normally Obtainable)
- Can be obtained at the command blocks that control everything by clicking the labeled sign
- Tells all features that come with this as well as information on all items and crafting

Download comes with:
- World download with command blocks
- Schematic of command blocks
- Note: You can find all items in a double chest at the command block mechanic

Using it in your world:
- Once pasted into your world, simply flick the lever up at the starting area to power the bird mechanic and press the button to create all scoreboards

- If you'd like to change the probability of bird chirping, bird flying, nest spawning, and/or bird spawning, you'll have to take out wool items from the hoppers that are facing into droppers in the randomizer. The more you take out, the more likely it will occur. From the hopper clock to the longer end, the hoppers link (you can see to where by following the redstone trail) from bird chirping, bird flying, nest spawning, then bird spawning. Current probabilities are 1/9, 1/81, 1/729, and 1/6561 respectively.

Easter Egg (shh!)
Turn Birds into Notch Birds! (Use on already existing birds)

Adult birds:
/entitydata @e[​name=birdbigm] {Equipment:[{id:minecraft:skull,Count:1b,Damage:3s,tag:{display:{Name:"Notch"},SkullOwner:{Id:3B6671CB-52F8-2ED6-1C41-ABA9F84EC02D,Properties:{textures:{Value:e3RleHR1cmVzOntTS0lOOnt1cmw6Imh0dHA6Ly9pLmltZ3VyLmNvbS9HY2FOUGhsLnBuZyJ9fX0==}]}}} }]}

Baby birds:
/entitydata @e[​name=birdm] {Equipment:[{id:minecraft:skull,Count:1b,Damage:3s,tag:{display:{Name:"Notch"},SkullOwner:{Id:3B6671CB-52F8-2ED6-1C41-ABA9F84EC02D,Properties:{textures:{Value:e3RleHR1cmVzOntTS0lOOnt1cmw6Imh0dHA6Ly9pLmltZ3VyLmNvbS9HY2FOUGhsLnBuZyJ9fX0==}]}}} }]}