Lying west of Mona Island is an uninhibited rocky outcrop, called Monito Island. Part of the Mayaguez municipality of Puerto Rico, the island measures only 0.15 square kilometre and rises to a height of 65 meters above sea level.  

Likewise Mona Island, Monito Island is also a nature reserve with 37 species and 36 genera of flora found here. The largest of these plant families are the Cactacceae, Poaceae and Malvacceae.  

Among the fauna are the nesting birds Brown Bobby, colonies of which are found all over the tiny island. On the beaches, various kinds of seabirds can be found. Being very disruptive birds, can be major cause for the absence of other winged species. An endangered speice of geckos, called the Monito Gecko is also found on this island.  

The island is quite flat on the southern and western edges, while rising up a little at the northeastern side. The whole island is completely covered by a low shrubby vegetation which dominated by Capparis flexuosa, Ficus citrifolia, Pithecellobium unguis-cati, and Guapira discolor.  

The southern and western portions are relatively flat and the highest elevations are toward the northeast, with a maximum of 63 m near the northeastern corner. A north-south fissure extends through the lowlands on the south side.