Corcovado offers Costa Rica's best wildlife viewing with virtually guaranteed sightings of diverse species. Commonly seen mammals: All four monkey species (howler, white-faced capuchin, spider, and squirrel monkeys—often in large troops), two-toed and three-toed sloths, white-nosed coatis (traveling in groups of 20+), agoutis (large rodents), collared peccaries (wild pig relatives traveling in herds), northern tamanduas (anteaters—less common but frequently spotted at Sirena), and incredibly, Baird's tapirs—Corcovado is one of few places in the world where these endangered gentle giants are regularly seen, especially near Sirena Station. Birds: Flocks of scarlet macaws (50+ birds together—breathtaking sight), toucans, trogons, tanagers, oropendolas, woodpeckers, and over 400 species total making it a birder's paradise. Reptiles and amphibians: American crocodiles (sometimes spotted catching prey at river mouths), boa constrictors, fer-de-lance snakes, poison dart frogs, and countless other species. Rarely but possibly seen: Jaguars, pumas, ocelots (Corcovado has highest big cat density in Costa Rica but they remain elusive), tayras, and giant anteaters. One overnight visitor reported seeing: "Tapir, all four monkeys, coatis, agouti, peccaries, sloths, tamandua, boa constrictors, a crocodile eating its kill, a tayra and more." Wildlife density at Sirena Station is extraordinary—animals concentrate there and are accustomed to humans, providing close encounters impossible elsewhere. However, the jungle is not a zoo—sightings depend on season, weather, luck, and especially guide skill. Early morning starts and overnight stays dramatically increase viewing opportunities.