Minecraft wiki entry for Chicken, associated text: Chickens are the only Overworld mob that can breed without a separate item. Chickens lay eggs at random, and an egg thrown at the ground has a 1⁄8 chance of spawning a chick. If a chick spawns from a thrown egg, there is a further 1⁄32 chance (overall 1⁄256 per egg) to spawn 3 extra chicks. It is theoretically possible for a stack of 16 eggs to yield 64 chickens, if all spawn chances succeed for all eggs.