Sheep

 are livestock animals that can be sheared when full to obtain Fleece. See Livestock for details.

Whenever there are fewer than 4 left on the map (2 for small worlds), one will spawn in on a random Grass tile.

Feed Efficiency
will become full at 25 energy.

If shears have been unlocked, they will wait up to 60 seconds to be shorn before becoming hungry again, but will wait indefinitely in a Crude Shearing Shed.