The only mammal native to Puerto Rico [1] is the bat. Eleven species live on the island, including the red fig-eating bat, which roosts in the forest canopy in the Caribbean National Forest, and the Greater Antillean long-tongued bat, which lives in caves and feeds on fruits and nectar from flowers.
Thanks to colonial trade ships, rats were introduced to the island in the late 1400s. They thrived here in great abundance, causing havoc on sugar plantations. Then someone had the brilliant idea of introducing mongooses from India to keep the rat population down. Unfortunately, mongooses are active during the day, and rats are active at night, so the effort failed, and now there’s a mongoose problem. They have no natural predators on the island, and they live up to 40 years. Mongooses are to be avoided at all costs as they are major carriers of rabies.
Paso Fino horses are a common form of transportation in rural areas of Puerto Rico [1], especially in Vieques [2] and Culebra [3], where they roam the island freely.
Some parts of Puerto Rico also have a feral dog problem. It’s not uncommon to see roving packs of mangy, skeletal canines rummaging for scraps in small towns and rural areas.
Links:
[1] http://www.moon.com/destinations/puerto-rico
[2] http://www.moon.com/destinations/puerto-rico/vieques-and-culebra/vieques
[3] http://www.moon.com/destinations/puerto-rico/vieques-and-culebra/culebra