Cerro San Gil contains almost 50% of the total biodiversity of the country: 54% of all known vertebrate species, including 56% of amphibians, 48% of reptiles, and 67% of bird species can be found in this unique rainforest. Because of its topography and geological history, Cerro San Gil also has high levels of endemism in its flora and fauna, especially in the lowlands of the Tamejá and Las Escobas watersheds. The few studies carried out in the region have found endemic species of amphibians, trees, palms and insects, thus confirming the importance of this forested remnant at the national and regional levels. In Cerro San Gil, there are at least 84 species of mammals; some of these species need large tracts of forests and/or natural habitat to ensure their survival, including Jaguar (Panthera onca) (NT), and Baird’s Tapir (Tapirus bairdii) (EN). San Gil is also one of the most biodiverse areas for bats in Guatemala, with 36 species.
Guatemala’s Caribbean Region is a center of endemism for amphibians, particularly for the genus Craugastor (or Eleutherodactylus, family Brachycephalidae). In Cerro San Gil, two endemic species of this genus have been reported, Bob’s Robber Frog (Craugastor campbelli) and a new species (C. sp. nov.), as well as two endemic species of salamanders, Bonita Moss Salamander (Nototriton stuarti) (DD) and an undescribed species (Oedipina sp. nov.). Also, 31 species of endemic plants have been described for Cerro San Gil.
Cerro San Gil is a registered Important Bird Area for Guatemala, and is a key stopover and wintering habitat for more than 100 migratory birds. Many of these species have population declines and are considered threatened. In particular, there are several species dependent on lowland forests with population declines: Wood Thrush (Hylocichla mustelina), Tennessee Warbler (Vermivora peregrina), Chestnut-sided Warbler (Dendroica pensylvanica), Louisiana Waterthrush (Parkesia motacilla) and Kentucky Warbler (Oporornis formosus). With a total over 423 species of birds, Cerro San Gil is a haven for resident and migratory birds in Caribbean Guatemala.