[3] The region is one of high biodiversity, as the area is the meeting zone where North and South American floral and fauna communities mixed when the continents were connected three million years ago.

Native mammals include the white-lipped peccary (Tayassu pecari), jaguar (Panthera onca), margay (Leopardus wiedii), Central American spider monkey (Ateles geoffroyi), Central American squirrel monkey (Saimiri oerstedii), Panamanian night monkey, (Aotus zonalis), giant anteater (Myrmecophega tridactyla), Handley's tailless bat (Anoura cultrata), Talamancan yellow-shouldered bat (Sturnira mordax), spectral bat (Vampyrum spectrum), and yellow isthmus rat (Isthmomis flavidus).

Some near-endemic birds are altitudinal migrants, moving between the ecoregion and the higher-elevation Talamancan montane forests to the north.

Endemic and near-endemic birds include the brown-backed dove (Leptotila battyi), Costa Rican swift (Chaetura fumosa), Veraguas mango (Anthracothorax veraguensis), white-crested coquette (Lophornis adorabilis), charming hummingbird (Polyerata decora), Baird's trogon (Trogon bairdii), fiery-billed araçari (Pteroglossus frantzii), golden-naped woodpecker (Melanerpes chrysauchen), black-hooded antshrike (Thamnophilus bridgesi), Coiba spinetail (Cranioleuca dissita), orange-collared manakin (Manacus aurantiacus), turquoise cotinga (Cotinga ridgwayi), riverside wren (Cantorchilus semibadius), spot-crowned euphonia (Euphonia imitans), black-cheeked ant tanager (Habia atrimaxillaris), and Cherrie's tanager (Ramphocelus costaricensis).

[6] Endemic amphibians include the Airstrip caecilia (Oscaecilia osae), so-called because it is only found near the La Sirena airstrip on the Osa Peninsula, the critically endangered Golfito robber frog (Eleutherodactylus taurus), and the endangered Golfodulcean poison frog (Phyllobates vittatus).