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The island of Borneo, located in southeast Asia at the southern edge of the South China Sea, is home to one endemic bird family, three endemic bird genera and 59 endemic bird species. All but one of the latter are forest dwellers, with most restricted to the spine of hills and mountains running down the middle of the island. The avian endemism has been shaped by the island's geological history. Borneo sits on a continental shelf. During glacial periods, when water levels were lower, Borneo was linked with other islands on the shelf and with the Malay peninsula in a large landmass known as Sundaland. This allowed bird species to move freely throughout the region until the waters rose again as the glaciers melted. Separated from their relatives by the sea, some of these species evolved over millennia into the endemics now found on the island. BirdLife International has designated the mountainous central spine of the island as an Endemic Bird Area (EBA) because of the number of endemic species found there, and has further designated several lowland regions and nearby islands as secondary EBAs. Habitat destruction is a major threat to Borneo's endemic birds, as forests are lost to palm oil plantations and timber harvesting.

Geology and geological history

Borneo is an island located in southeast Asia, on the continental shelf at the southern edge of the South China Sea. It lies south of the Philippines, west of Sulawesi, north of Java, and east of peninsular Malaysia. With an area of 748,168 km² (288,869 sq mi), it is the world's third largest island. More than half of the island is lowlands, rising to less than 150 m (490 ft). However, a spine of mountains runs down much of the central portion of the island. These include Mount Kinabalu, which at 4,095 m (13,435 ft) is the tallest mountain between the Himalayas and West Papua. The island is shared by three countries: Indonesia, Malaysia, and Brunei.[1] While the lowlands are the most productive habitat in terms of the number of bird species found there, the mountains are the seat of Borneo's endemism.[2] This is in large part due to the island's geological history.[3]

During the Pleistocene, the world's polar caps repeatedly advanced and retreated, alternately locking vast amounts of water into ice, and releasing it back into the world's oceans. This caused the water level in the oceans to repeatedly rise and fall. During glacial periods, when water levels were at their lowest, much of the Sunda Shelf was exposed. This linked what are now discrete islands (including Borneo, Java, Sumatra, and a host of smaller islands) with the Malay peninsula in one large landmass known as Sundaland. During periods when the shelf was exposed, birds could move freely across the whole landmass. When the waters rose again, these birds were cut off from their relatives, and evolved in isolation on the various islands. Temperatures were cooler overall during glacial periods, so montane birds (those generally restricted to the slopes of mountains) could move lower and spread across larger areas. During interglacial periods, they retreated to higher elevations and were separated again from other populations, including birds in the lowlands.[3][4] Studies have shown that some endemic montane species are most closely related to species in Borneo's lowlands, while others are more closely related to montane species on other Sundaland islands.[5]

Endemism and threats

The island is home to a single endemic family: Pityriaseidae, which contains a single endemic genus (Pityriasis) with a single endemic species, the Bornean bristlehead.[6] In addition, the island holds two other endemic genera, both of which are also monotypic: Chlamydochaera (the fruithunter) and Haematortyx (the crimson-headed partridge).[6] Two other monotypic genera formerly considered to be endemic to the island—Chlorocharis and Oculocincta—have since been merged into more widespread genera. Chlorocharis was merged into the large white-eye genus Zosterops after molecular studies showed it nested comfortably within that genus. The same studies showed that Oculocincta was embedded within the smaller white-eye genus Heleia, leading it to be moved as well.[7][8][9]

There are 59 endemic bird species on Borneo, according to the taxonomy proposed by the International Ornithologists' Union.[9] Nearly all of these are forest birds; only the dusky munia is not. In all, roughly 10% of Borneo's forest birds are endemic to the island. Of these, 60% are montane species, 30% are found on lower slopes, and 10% are lowland species.[10] However, Borneo's forests are under threat, particularly in the lowlands. Nearly 40% of the island's forests had been completely cleared by 2016, and another 34% had been selectively logged.[11] Some 80% of Kalimantan's forests have been sold to timber concessions.[12] Much of the original lowland forest has been converted to palm oil plantations; these now cover more than 32% of Kalimantan's lowland area.[11] This results in a huge loss of biodiversity. While the original dipterocarp forests are home to more than 220 bird species, for example, palm plantations support only about 14 resident species.[13] Some 80% of Kalimantan's forests have been opened up to timber concessions, even in protected areas.[12][14] Many highland forests fall into protected areas—including national parks and forest reserves—but such gazetting does not always guarantee true protection, with logging occurring even in those areas.[15]

Endemic Bird Areas

Birdlife International defines Endemic Bird Areas (EBAs) as places where the breeding ranges of two or more range-restricted species—those with breeding ranges of less than 50,000 km² (19,000 sq mi)—overlap. In order to qualify, the whole of the breeding range of at least two range-restricted species must fall entirely within the EBA.[17] Borneo has one such area. The Bornean mountains EBA (157) comprises 130,000 km² (50,000 sq mi) of mountain ranges in Borneo's interior, at an altitude above 500 m (1,600 ft) in elevation. These mountains are found in all three countries which share the island. Two of Borneo's three endemic genera are found here; only the Borneo bristlehead is found at lower elevations. In total, 31 range-restricted species occur within this EBA.[18]

BirdLife International has also designated five Secondary EBAs for Borneo: two smaller island groups and three areas on Borneo itself. Secondary EBAs are those which either include the breeding range of only a single range-restricted species, or those which cover only part of a range-restricted bird's breeding area.[19]

• The North-east Bornean islands secondary area (s097) includes a number of small islands off the northern and eastern coasts of Borneo.[20] The grey imperial pigeon, which the International Union for Conservation of Nature (IUCN) considers to be a vulnerable species, is found on a dozen or so of the islands; the near threatened, range-restricted Mantanani scops owl is more common and widespread on the small islands off Sabah. Both species also breed on small islands near the Philippines. Three designated Important Bird Areas (IBAs) fall within this area.[20]

• The Sabah lowlands secondary area (s098) encompasses the lowlands of the Malaysian state of Sabah, at the northern end of Borneo. The breeding range of the white-fronted falconet, a near-threatened species, falls entirely within the area. Part of the breeding range of the white-crowned shama is also included. The secondary area includes eight designated IBAs.[21]

• The Kalimantan lowlands secondary area (s099) encompasses the lowland forest thought to contain the breeding range of the black-browed babbler, a presumably threatened species recently rediscovered, more than 170 years after the only specimen was collected.[22][23] There are no IBAs in this secondary area.[22]

• The Bornean coastal zone secondary area (s100) includes mangroves, coastal forest, and scrub on the island's western and southern coasts. These lie in the Malaysian state of Sarawak, and the Indonesian provinces of Kalimantan Barat, Kalimantan Selatan and Kalimantan Tengah. Part of the breeding area of the range-restricted Javan white-eye is found here; the vulnerable species also breeds on the Javan coast. The secondary area includes one designated IBA.[24]

• The Natuna Islands secondary area (s101) includes small islands in an archipelago located off the western coast of Borneo. The critically endangered and range-restricted silvery pigeon occurs in very small numbers here; it also occurs on Sumatra and a few smaller islands just off Sumatra's coasts.[25][26] One designated IBA lies within this zone.[26]

List of endemic species

IUCN Red List categories

Conservation status
EX	Extinct (0 species)
EW	Extinct in the wild (0 species)
CR	Critically Endangered (0 species)
EN	Endangered (1 species)
VU	Vulnerable (5 species)
NT	Near threatened (12 species)
LC	Least concern (39 species)
Other categories
DD	Data deficient (2 species)
NE	Not evaluated (2 species)

Endemic species

Taxon. order[nb 1]	Common name	Picture	Scientific name	Habitat	IUCN status[nb 2]	Notes	EBA
1	Hose's partridge		Rhizothera dulitensis	Hill and lower montane forest[28]	VU IUCN	Also known as Dulit partridge[29]
2	Red-breasted partridge		Arborophila hyperythra	Hill dipterocarp forest; lower and upper montane forest[30]	LC IUCN	Also known as Bornean partridge[31]	157
3	Crimson-headed partridge		Haematortyx sanguiniceps	Hill dipterocarp forest; lower and upper montane forest[30]	LC IUCN		157
4	Bulwer's pheasant		Lophura bulweri	Hill and lower montane forest[32][33]	VU IUCN
5	Bornean peacock-pheasant		Polyplectron schleiermacher	Lowland and hill dipterocarp forest[33][34]	EN IUCN
6	Dulit frogmouth		Batrachostomus harterti	Hill dipterocarp forest; lower montane forest[30]	NT IUCN		157
7	Bornean frogmouth		Batrachostomus mixtus	Hill dipterocarp forest; lower montane forest[30]	NT IUCN
8	Bornean swiftlet		Collocalia dodgei	Upper montane forest[35][36]	LC IUCN	Sometimes considered to be a subspecies of the cave swiftlet or the glossy swiftlet[37]
9	Bornean ground cuckoo		Carpococcyx radiceus	Lowland primary dipterocarp and riverine forest[38][39]	NT IUCN
10	Mountain serpent eagle		Spilornis kinabaluensis	Upper montane forest[30]	VU IUCN		157
11	Whitehead's trogon		Harpactes whiteheadi	Lower and upper montane forest[30]	NT IUCN		157
12	Mountain barbet		Psilopogon monticola	Lower and upper montane forest[30]	LC IUCN		157
13	Golden-naped barbet		Psilopogon pulcherrimus	Upper montane forest[30]	LC IUCN		157
14	Bornean barbet		Psilopogon eximius	Lower and upper montane forest[30]	LC IUCN		157
15	Brown barbet		Caloramphus fuliginosus	Lowland dipterocarp forest and lower hill forest, swamp forest and kerangas forest[40][41]	LC IUCN	Sometimes known as the Bornean brown barbet[42]
16	White-fronted falconet		Microhierax latifrons	Lowland dipterocarp forest[43][44]	NT IUCN		s098
17	Hose's broadbill		Calyptomena hosii	Hill dipterocarp forest; lower montane forest[30]	NT IUCN		157
18	Whitehead's broadbill		Calyptomena whiteheadi	Lower and upper montane forest[30]	LC IUCN		157
19	Bornean banded pitta		Hydrornis schwaneri	Lowland and hill dipterocarp forest[45][46]	LC IUCN
20	Blue-headed pitta		Hydrornis baudii	Lowland dipterocarp forest[45][46]	VU IUCN
21	Black-crowned pitta		Erythropitta ussheri	Lowland dipterocarp forest[45][47]	NT IUCN
22	Blue-banded pitta		Erythropitta arquata	Hill and lower montane forest, particularly bamboo groves[45][47]	LC IUCN
23	Bornean bristlehead		Pityriasis gymnocephala	Lowland and hill dipterocarp forest[48][49]	NT IUCN
24	Bornean whistler		Pachycephala hypoxantha	Lower and upper montane forest[30]	LC IUCN		157
25	Black oriole		Oriolus hosii	Lower and upper montane forest[30]	NT IUCN		157
26	Bornean black magpie		Platysmurus aterrimus	Lowland forest and swamp forest	LC IUCN	Formerly considered to be a subspecies of the black magpie; split in 2021
27	Bornean green magpie		Cissa jefferyi	Lower forest[48][50]	LC IUCN
28	Bornean treepie		Dendrocitta cinerascens	Hill dipterocarp forest; lower and upper montane forest[48][50]	LC IUCN
29	Charlotte's bulbul		Iole charlottae	Lowland and hill dipterocarp and peat swamp forests[51][52]	NT IUCN	Sometimes considered to be a subspecies of the buff-vented bulbul[53]
30	Bornean bulbul		Rubigula montis	Lower and upper montane forest[54][55]	LC IUCN
31	Cream-eyed bulbul		Pycnonotus pseudosimplex	Lowland and hill dipterocarp and peat swamp forests; lower montane forests[56][57]	LC IUCN
32	Pale-faced bulbul		Pycnonotus leucops	Upper montane forest[54][58]	LC IUCN	Sometimes considered to be a subspecies of the flavescent bulbul[59]
33	Bornean stubtail		Urosphena whiteheadi	Hill dipterocarp forest; lower and upper montane forest[30]	LC IUCN		157
34	Friendly bush-warbler		Locustella accentor	Upper montane forest[30]	LC IUCN		157
35	Chestnut-crested yuhina		Staphida everetti	Hill dipterocarp forest; lower and upper montane forest[30]	LC IUCN		157
36	Pygmy white-eye		Heleia squamifrons	Hill dipterocarp forest and lower montane forest[30]	LC IUCN		157
37	Mountain blackeye		Zosterops emiliae	Upper montane forest[30]	LC IUCN		157
38	Bare-headed laughingthrush		Melanocichla calva	Lower and upper montane forest[30]	LC IUCN		157
39	Black-throated wren-babbler		Turdinus atrigularis	Lowland dipterocarp forest[60][61]	NT IUCN
40	Black-browed babbler		Malacocincla perspicillata	Probably lowland forest[62][63]	DD IUCN	Rediscovered in 2019, more than 170 years after the only specimen was collected[23]	s099
41	Mountain wren-babbler		Gypsophila crassa	Lower and upper montane forest[30]	LC IUCN		157
42	Bornean wren-babbler		Ptilocichla leucogrammica	Lowland dipterocarp and peat swamp forests; kerangas forest[60][64]	VU IUCN
43	Chestnut-hooded laughingthrush		Pterorhinus treacheri	Hill dipterocarp forest; lower and upper montane forests[65][66]	LC IUCN
44	Everett's thrush		Zoothera everetti	Lower and upper montane forest[30]	NT IUCN		157
45	Fruithunter		Chlamydochaera jefferyi	Lower and upper montane forest[30]	LC IUCN		157
46	White-crowned shama		Copsychus stricklandii	Lowland and hill dipterocarp and peat swamp forests; lower montane forest[67][68]	LC IUCN	Sometimes considered to be a subspecies of the white-rumped shama[69]
47	Dayak blue flycatcher		Cyornis montanus	Montane forest	LC IUCN	Sometimes considered to be a subspecies of the hill blue flycatcher (aka Javan blue flycatcher)	157
48	Bornean blue flycatcher		Cyornis superbus	Lowland and hill dipterocarp forest[70][71]	LC IUCN
49	Crocker jungle flycatcher		Cyornis ruficrissa	Montane forest	Not recognised by IUCN	Sometimes considered to be a subspecies of the Philippine jungle flycatcher	157
50	Eyebrowed jungle flycatcher		Vauriella gularis	Lower and upper montane forest[30]	LC IUCN		157
51	Bornean forktail		Enicurus borneensis	Streams in lower to upper montane forest[72][73]	Not recognised by IUCN	Sometimes considered to be a subspecies of the white-crowned forktail[74]
52	Bornean whistling thrush		Myophonus borneensis	Lower and upper montane forest[75][73]	LC IUCN
53	Bornean leafbird		Chloropsis kinabaluensis	Lower and upper montane forest[76][77]	LC IUCN
54	Yellow-rumped flowerpecker		Prionochilus xanthopygius	Lowland, hill and lower montane forest[78][79]	LC IUCN
55	Spectacled flowerpecker		Dicaeum dayakorum	Lowland and hill dipterocarp forest[80][79]	DD IUCN	Described to science in 2019[81]
56	Black-sided flowerpecker		Dicaeum monticolum	Hill dipterocarp forest; lower and upper montane forest[30]	LC IUCN		157
57	Bornean spiderhunter		Arachnothera everetti	Lowland, hill, and lower montane forest[82][83]	LC IUCN	Sometimes considered to be a subspecies of streaky-breasted spiderhunter[84]
58	Whitehead's spiderhunter		Arachnothera juliae	Lower and upper montane forest[30]	LC IUCN		157
59	Dusky munia		Lonchura fuscans	Scrub, gardens, grasslands, and rice paddies[85][86]	LC IUCN

See also

• Deforestation in Borneo

Notes

Citations

References

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