This site is entirely covered with primary rainforest over an altitudinal range of 300–1,250 m. At 1,250 m, Monte Alen and Monte Mitra (also within the National Park) are thought to be the highest massifs in mainland Equatorial Guinea, although altitudinal information is incomplete. The park is bordered by the large and fast-flowing Uoro river to the west, while the main road from Niefang to Gabon forms the eastern boundary. There are no natural savannas, although some small areas of exposed rock with low bush occur locally near the summit; one small lake (Lake Atoc) is entirely surrounded by forest.
See Box and TableS 2 and 3 for key species. At least 265 species have been recorded from the park. Of special note is the recent discovery of three montane species: Coracina caesia (at 750 m), Dryoscopus angolensis (common above 1,100 m) and Phylloscopus herberti (common above 800 m). Phylloscopus budongoensis also occurs (from 325 m), and this site is the only one known so far in central Africa where these congeneric warblers coexist. P. herberti is also a restricted-range species of the Cameroon mountains EBA (086) (see Table 2); both it and C. caesia are, in addition, restricted to the Afrotropical Highlands biome (A07). Picathartes oreas is widespread and, indeed, its specialized habitat is well represented throughout the park. Other species of interest include Melignomon zenkeri (apparently not uncommon at forest edges), Muscicapa tessmanni and Batis minima (both recorded from open-canopy forest). There is a possible sight record of Apus sladeniae, but identification of this swift is so difficult that confirmation is necessary.
Non-bird biodiversity: Among the primates are Colobus satanas (VU, quite common), as well as Cercocebus torquatus (LR/nt), Mandrillus sphinx (LR/nt), Gorilla gorilla (EN) and Pan troglodytes (EN). There are small numbers of elephant Loxodonta africana (EN). The rare shrew Crocidura grassei (VU) has been collected. The frog Conraura goliath (VU) occurs at the southern limit of its distribution.
BirdLife International (2020) Important Bird Areas factsheet: Monte Alen National Park. Downloaded from http://www.birdlife.org on 24/01/2020.