Chicken

Chickens (also known as Ducks ) are passive mobs.

Natural generation
Chickens naturally generate on grass blocks with 2 blocks of free space above it at light level of 9 or more.

Baby chicken


Chickens can be bred with wheat seeds (or beetroot seeds in Pocket Edition).

Growth of chicks can be accelerated by wheat seeds; each item adds 10% of the remaining time.

Other
Thrown eggs have an $1/8$ chance to spawn a baby chicken. After that, there is a $1/32$ chance to spawn 4 chicks instead.

If the egg was thrown at a wall at certain angles, the chicken may spawn in the wall and either suffocate (opaque blocks) or pass through entirely (transparent blocks).

Behavior
Chickens are 0.875 blocks tall, 0.5 blocks wide and 0.8125 blocks long.

Chickens appear to wander around aimlessly, without attempting to stay out of water or avoid falls. When falling they will flap their wings quickly and fall slowly. They are immune to fall damage.

While in a loaded chunk, a chicken will lay one egg every 5 to 10 minutes (6000 to 12000 ticks), unless it is or was a part of a Chicken Jockey.

They share some behaviors with other "farm animals":
 * They are drawn to light when in a dark environment.
 * When struck, they run around quickly and aimlessly.
 * They can swim, visibly flapping their wings as they stay on the surface,
 * They can be led around by holding a seed, and are also able to breed with seeds.

Chickens are attacked by wild ocelots.

Chicks do not lay eggs. Due to their small size, they can pass through openings even smaller than a full block. A chick's height is somewhere in between 0.51 to 0.80 blocks.

Trivia

 * When a chicken is killed off a ledge, the corpse also falls more slowly than normal, and the wings still make a flapping animation.
 * Chickens are able to "hide" within hoppers due to their small size, protecting them from lava or water that might be directly on top of the hopper.
 * A few weeks before the end of Beta, Notch tweeted that he changed the chickens to ducks, causing a turmoil on Twitter. A few days later, Jeb, still getting feedback on the idea, stated that it was just a joke.
 * While you are loading/creating/exiting a world in a Console Edition, the message that appears can say "Is it a Chicken, or a duck?". Also, the summary for the mobs avatars at the end says "... and a chicken... Or is it a duck?".