The La Fortuna area is excellent for wildlife despite its level of tourism. The forests around the volcano and along the rivers hold sloths (both two-toed and three-toed), howler and spider monkeys, dozens of frog species including the iconic red-eyed tree frog, caimans along the Laguna de Arenal and smaller waterways, and over 400 bird species. Toucans — specifically the keel-billed toucan and the collared aracari — are almost comically common. Hummingbirds are attracted to the flowers at almost every lodge.
Early morning and late afternoon game drives (by vehicle) or walks produce the best results. The area around the Caño Negro wildlife refuge, about 90 minutes north near the Nicaraguan border, is worth a half-day trip for serious birders: a shallow lake system with exceptional waterbird concentrations. Several operators run guided night tours from La Fortuna that focus on frogs, insects, and nocturnal mammals — these are generally excellent value and require no special skills.