A chicken is a passive mob found in most grassy biomes, and the main source of raw chicken, feathers and eggs. They have three variants based on the temperature of the biome they spawn in. 

Chickens spawn naturally in the Overworld in most grassy biomes except snowy plains, meadows, cherry groves, mangrove swamps, and pale gardens.

Each chicken has a 5% chance of spawning as a baby.

In Java Edition, chickens spawn in groups of 4 on grass blocks in any light level. Individual chickens rarely may spawn after world generation.

In Bedrock Edition, chickens spawn in groups of 2-4 on grass blocks in a light level of 7 and more. Individuals regularly spawn after world generation.

In Java Edition, chickens are more common in sparse jungles.

In Java Edition, chickens may be found in the Nether when a baby zombified piglin spawns as a chicken jockey. This can also happen with every other baby variant of the zombie.

A chicken normally wanders aimlessly when idle. Sometimes they remain in a small area, even if it's just a 1 block space. They follow players holding various seeds within a 6×4×6 cubic area. Chicks follow adult chickens.

Chickens avoid falling off cliffs (>3.5 blocks). They flap their wings when they are in midair and fall slowly, thus chickens are immune to fall damage.

Chickens can be attached to leads.

When harmed, chickens flee around for a few seconds.

Unlike other mobs, chickens attempt to jump up to climb stairs instead of climbing them normally.[1]

Ocelots, untamed cats‌[JE only], and foxes pursue and attack chickens. While chickens do flee when attacked, they otherwise make no attempt to avoid foxes.

While in a loaded chunk, an adult chicken lays an egg every five to ten minutes (6000–12000 ticks), unless it is, or was, a part of a chicken jockey. If the player is close enough to a chicken when it lays an egg, a pop sound is heard.

Chickens can stay underwater for 15 seconds or can swim, visibly flapping their wings and staying on the water surface. While swimming, a chicken needs only one block of air above its head.