Ornithologists have described two new species of the flycatcher genus Cyornis and the white-eye genus Zosterops from southeastern Borneo, Indonesia.
Cyornis is a genus of passerine birds in the Old World flycatcher family Muscicapidae.
This genus contains 25 currently recognized species, including some species that were previously placed in the genus Rhinomyias.
It is distributed throughout southern Asia, from the Indian subcontinent to Southeast Asia, the Philippines and Indonesia.
Most Cyornis flycatchers are sexually dimorphic in plumage, with males being blue above and mainly blue and white or orange and white below, although a few species are sexually monomorphic and lack bright colors.
Zosterops is a genus of passerine birds containing the typical white-eyes in the family Zosteropidae.
The genus comprises over 100 species distributed in the Afrotropical, Indomalayan, and Australasian realms.
These birds are supreme island colonizers, which is why so many different white-eye species have evolved so rapidly, as different island populations become isolated and split off from their source population.
The most characteristic feature of Zosterops white-eyes is a conspicuous white feather ring around the eye, though some species lack it.
The new Cyornis and Zosterops species inhabit the Meratus Mountains of southeastern Borneo.
“The avian biodiversity and endemism of Borneo is impressive, with some 50 endemic species described from the island under earlier taxonomic arrangements,” said co-author James Eaton of Birdtour Asia Ltd. and his colleagues.
“Many of these are montane specialists, with around 27 species endemic to Borneo’s highlands.”
“Although the mountains of the Malaysian states, Sabah and Sarawak, are relatively well-explored, much of the montane part of Indonesia’s Kalimantan provinces has seldom been visited.”
“One of the least-known areas and probably the most isolated mountain range are the Meratus Mountains, South Kalimantan province, a 140 km long north-south arc of uplands clothed with about 2,460 km2 of submontane and montane forest, rising to the 1,892 m summit of Gn Besar (several other peaks exceed 1,600 m).”
The new Cyornis species is most closely related to the Dayak blue flycatcher (Cyornis montanus) but morphologically distinguished by lighter blue on the upperparts and more whitish and less reddish on the underparts.
The new Zosterops species is most closely related to the lemon-bellied white-eye (Zosterops chloris) but distinguished by olive upperparts and darker underparts.
“Both new species are probably confined to the Meratus Mountains, which are currently surrounded by degraded lower elevation secondary woodland or converted agricultural landscape,” the researchers said.
“They appear to have diverged from their sister species through geographic isolation in this remote mountain range compounded by altered population dynamics in a depauperate montane bird community.”
“Although both species are relatively common in the restricted area of the Meratus Mountains, continued habitat alteration and the imminent threat of poaching may be in the process of endangering them.”
“Therefore, we recommend the IUCN Red List status of Vulnerable for the new species based on criteria B1 and B2.”
The Meratus flycatcher and white-eye are described in a paper published in the Journal of Ornithology.
M. Irham et al. Description of two new bird species from the Meratus Mountains of southeast Borneo, Indonesia. J Ornithol, published online January 11, 2022; doi: 10.1007/s10336-021-01937-2
J.A. Eaton et al. 2016 A short survey of the Meratus Mountains, South Kalimantan province, Indonesia: two undescribed avian species discovered. BirdingASIA 26: 107-113
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