In the Iberian Peninsula and the Americas, a burro is a small donkey. The Domestic Animal Diversity Information System (DAD-IS) of the FAO lists the burro as a specific breed of ass. In Mexico, the donkey population is estimated at three million. There are also substantial burro populations in El Salvador, Guatemala, and Nicaragua. Burro is the Spanish and Portuguese word for donkey. In Spanish, burros may also be called burro mexicano ('Mexican donkey'), burro criollo ('Criollo donkey'), or burro criollo mexicano. In the United States, "burro" is used as a loan word by English speakers to describe any small donkey used primarily as a pack animal, as well as to describe the feral donkeys that live in Arizona, California, Oregon, Utah, Texas and Nevada.Among donkeys, burros tend to be on the small side.