The most important feature of the Rio Bravo is that it appears to support complete and fully functioning faunal communities characteristic of the area. Populations are for the most part healthy, including those of species that are under pressure elsewhere in the Central American range. Over 70 mammal species and 350 bird species have been recorded in the Rio Bravo.
The fauna has also been well-studied with research and survey projects covering all the major groups. In general terms diversity is high including foraging and breeding habitat for a range of species of conservation concern. As with the flora the most important characteristic is that they occur in fully functioning communities characteristic of the area, most clearly demonstrated by the diversity and relative commonness of top predators (large cats, birds of prey). The area has therefore been selected for re-introduction of the globally threatened Harpy Eagle, Harpia harpyja, a species highly dependent on extensive areas of unbroken forest.
The bird population is very diverse with at least 350 species, , including 9 Yucatan endemics and a substantial proportion of migrant species. Five are red-listed, of which one is endangered and the rest have limited ranges: great curassow Crax rubra, black rail Laterallus jamaicensis, ocellated turkey Meleagris ocellata, crested eagle Morphnus guianensis, and yellow-headed parrot Amazona oratrix. Recent survey work indicates that the avifauna includes 38 species considered imperilled, vulnerable, or of conservation concern under criteria used by international conservation agencies.
The known mammal fauna includes over 70 species. of which more than half are bats. Some 9 species are red-listed – Mexican black howler monkey Alouatta palliata mexicana, Yucatan spider monkey Ateles geoffroyi yucatanensis, grey-headed tayra Eira barbara senex, river otter Lutra longicaudis, red brocket deer Mazama americana, false vampire bat Vampyrum spectrum, jaguar Panthera onca, Baird’s Tapir Tapirus bairdii, and manatee Trichecus manatus. The presence of a further two – cacomistle Bassariscus sumichrasti and Central American pygmy opossum Caluromys derbianus – has been reported but needs confirmation. Several species considered under pressure from hunting in the region – such as the four cat species apart from Jaguar that also occur, and both collared and white-lipped peccary Pecari tajacu and Tayassu pecari – are also present, as are two regional endemic squirrels. Four endemic rodent species have been reported in northern Belize and may be expected on the Rio Bravo .
The insect fauna undertaken between 1996 and 1999 contain a number of new country records, important extensions in known range, and unidentified – and probably new – species. This is, however, almost certainly a reflection of collecting effort rather than intrinsic site quality.
The fish fauna ……
The herpetofauna includes the following red-listed species: narrow-bridged musk turtle Claudius angustatus (limited range), Central American river turtle or hicattee Dermatemys mawii (endangered), Tabasco mud turtle Kinosternon acuta (limited range), common slider Trachemys scripta (limited range), and Morelet’s crocodile Crocodylus moreletii (limited range). All are frequent to common on the Rio Bravo and the area is considered a stronghold for the hicattee.