Caño Negro is one of the premier areas in the Americas to observe huge concentrations of both migratory and indigenous birds, along with reptilian river wildlife. The refuge is the only location in Costa Rica where the Nicaraguan Grackle regularly nests.

Caño Negro is created by the seasonal flooding of the River Frio so, depending upon what time of the year you visit, you may find yourself travelling around a broad lake in a motorboat or walking along mud-caked riverbeds. The rainy season is May-November when Caño Negro is at its fullest. However, the rainy season is not necessarily the best time to see most wildlife. The best time for birders is considered to be from January until March, when most migratory species of birds are in residence.