Black Rats (Rattus Rattus) were as common to ships as ship's biscuit in the 17th century. The dark isolated holds, the abundance of food and little danger from other animals made a ship an ideal home for rats. The nocturnal animal would eat just about anything on a ship including stored sails and ropes, wooden chests or even parts of the ship.
Although Mayflower must have had her share of rats making the voyage with the colonists, Governor William Bradford never mentioned them as one of the dangers they faced during the ocean crossing. This toy rat is the actual size of a Black Rat.