The EBA includes the mountain ranges in the interior of Borneo, the largest of the Greater Sunda Islands. These mountains extend into the territories of three different countries: the Indonesian provinces of Kalimantan Barat, Kalimantan Tengah, Kalimantan Timur and Kalimantan Selatan; the East Malaysian states of Sabah and Sarawak; and the nation of Brunei. The highest mountains present are those in Sabah in the north of the island, and these include Mt Kinabalu which rises to 4,094 m. High ranges with peaks of over 2,000 m extend southwards from here into southern Sarawak and northern and central Kalimantan.

The natural vegetation virtually throughout Borneo is tropical rain forest, and the restricted-range birds are mainly found in montane forest above c.1,000 m, although several occur below this altitude in hill dipterocarp forest on the lower mountain slopes (Wells 1985; see Whitmore 1984). The lower altitudinal limit of the EBA has been defined as the 500-m contour.

The Bornean mountains are rich in restricted-range species, and their distinctive avifauna includes four endemic genera, Haematortyx, Chlamydochaera, Oculocincta and Chlorocharis. A further 13 species are endemic to Borneo (Andrew 1992; see Collar and Long 1996), but all of these occur too widely in the lowlands to be treated as restricted-range species, other than Microhierax latifrons and Malacocincla perspicillata whose ranges define Secondary Areas s098 and s099 respectively.

Many of the mountains on Borneo are ornithologically unexplored or poorly known, particularly those in Kalimantan, so knowledge of the habitat requirements and distributions of the restricted-range birds within the EBA is inevitably incomplete (see Smythies 1981, Mann 1987, Davison 1992). Most of these species are found in both lower and upper montane forest, and some also range down into hill dipterocarp forest below 1,000 m. Batrachostomus harterti, Calyptomena hosii, Pycnonotus nieuwenhuisii and Oculocincta squamifrons were categorized as lowland-forest-slope specialists by Wells (1985), although most of them occur in lower montane forest as well as hill dipterocarp forest.

Several species appear to have particularly restricted ranges on Borneo, but in most cases this is probably a reflection of the uneven ornithological coverage of the island. Spilornis kinabaluensis, Otus brookii (in this EBA), Zoothera everetti, Garrulax calvus, Bradypterus accentor and Oriolus hosii are only recorded from East Malaysia (and Spilornis kinabaluensis in Brunei) in the northern and western parts of the EBA. However, some of these species probably occur also in Kalimantan, where recent survey work has resulted in the first Indonesian records of Harpactes whiteheadi, Megalaima pulcherrima, Rhinomyias gularis and Arachnothera juliae, and the first record of Zosterops atricapillus in Kalimantan (Robson 1993b, S. van Balen per Rudyanto in litt. 1996). Four species are not recorded from Sabah: Otus brookii, which is only known (in this EBA) from Mt Dulit in Sarawak, Batrachostomus harterti, Pycnonotus nieuwenhuisii, which is only known (in this EBA) by one specimen from Kalimantan and recent sightings in Brunei (and could be an extremely rare morph of another species, or be of hybrid origin: Williams in prep.), and Oriolus hosii, which is only recorded from Sarawak. None of the restricted-range birds has been recorded in the mountains of Kalimantan Selatan in the south-east of the EBA, but some of them are likely to occur in the montane forests there.

None of the restricted-range birds of this EBA is classified as threatened, although four are treated as Data Deficient, three of these because they are only known from a small number of records from relatively low altitudes, and the fourth, Spilornis kinabaluensis, because it probably has a small population and may be sensitive to minor degradation of its habitat. Thirteen more-widespread threatened species occur in the forests of Borneo, but these are mainly birds of the lowlands, and only in hill dipterocarp forest do they overlap in distribution with the restricted-range species which characterize the EBA-although Bulwer's Pheasant Lophura bulweri (classified as Vulnerable) also occurs in lower montane forest. The concentration of threatened species in the lowlands is a reflection of the fact that most forest loss and degradation on Borneo has taken place there, whereas the montane forests remain relatively untouched as yet (Collins et al. 1991).

Protected areas have been gazetted in all parts of this EBA, with several reserves in each of Kalimantan, Sabah, Sarawak and Brunei. Many of these contain large areas of montane and hill dipterocarp forest, and together they include well over 10% of the EBA. Crocker Range National Park and Kinabalu Park in Sabah are notable because they include the full range of habitat types found in the EBA, and therefore support populations of almost all of the restricted-range species. Several of the reserves in Kalimantan include very large areas of montane habitats within their boundaries, notably Sungai Kayan-Sungai Mentarang Nature Reserve, Gunung Penrissen-Gunung Nyiut Game Reserve, Gunung Bentuang Nature Reserve and Bukit Baka-Bukit Raya National Park.

Recommended citation
BirdLife International (2023) Endemic Bird Areas factsheet: Bornean mountains. Downloaded from http://datazone.birdlife.org/eba/search on 04/06/2023.