An international team of ornithologists led by Louisiana State University researchers has discovered a cryptic new species of bulbul in the Malaysian part of the island of Borneo.

An uniformly olive-brown bird called the cream-vented bulbul (Pycnonotus simplex) occurs from southern Indochina throughout the Sunda Islands, except Palawan in the south-western Philippines.

In most of its range, this species has white eyes. On the island of Borneo, however, most individuals have red eyes, although there are also a few with white eyes.

For more than a century, ornithologists have thought the eye-color difference on Borneo was a trivial matter of individual variation.

Through persistent detective work and advances in genetic sequencing technology, Louisiana State University researcher Subir Shakya and co-authors have discovered that the white-eyed individuals from Borneo in fact represent a completely new species — the cream-eyed bulbul (Pycnonotus pseudosimplex).

“One of the reasons we knew we had a new species as opposed to just a variant of another species was because the two populations — the red-eyed and white-eyed populations — actually occur together on Borneo,” Shakya said.

The scientists sequenced the DNA of several bird specimens from Sumatra and compared them to specimens from other sites in the region to determine the degree of genetic relatedness of various birds from the different islands and the mainland of Asia.

Several bulbuls from Borneo and the surrounding region were among the specimens they compared. However, the white-eyed cream-vented bulbuls from Borneo appeared genetically distinct from all the other white-eyed and red-eyed cream-vented bulbuls they examined.

Further work to understand this discrepancy led to the conclusion that the white-eyed birds from Borneo were in fact a new species.

“We had found white-eyed individuals of the bulbul in old-growth hill forest in Crocker Range National Park in 2008 and in Lambir Hills National Park in 2013; we also found them in Batang Ai National Park in 2018. All of these areas are in Malaysian Borneo,” said team member Dr. Fred Sheldon, also from Louisiana State University.

The discovery is outlined in the Bulletin of the British Ornithologists’ Club.

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Subir B. Shakya et al. 2019. A cryptic new species of bulbul from Borneo. Bulletin of the British Ornithologists’ Club 139 (1): 46-55; doi: 10.25226/bboc.v139i1.2019.a3