A team of ornithologists from the National University of Singapore, Birdtour Asia Ltd., and the University of Queensland has described a new and cryptic species of the hawk-cuckoo genus Hierococcyx from Borneo, a large island shared by the Malaysian states of Sabah and Sarawak, the Indonesian state of Kalimantan, and the sultanate Brunei.
Breeding range map of Hierococcyx bocki from Sumatra and Peninsular Malaysia, Hierococcyx sp. from Borneo, and Hierococcyx sparveriodes. Image credit: Ayuwat Jearwattanakanok / Robert O. Hutchinson / James A. Eaton.
Hierococcyx is a small genus of birds within the cuckoo family Cuculidae.
First established in 1845, the genus currently includes nine scientifically recognized species.
Commonly known as hawk-cuckoos, they can be found in South, Southeast, and East Asia.
“Within the hawk-cuckoos of the genus Hierococcyx, two tropical and subtropical Asian species form a close-knit pair,” said lead author Dr. Frank Rheindt from the National University of Singapore and his colleagues.
“They are variably merged into one species or recognized as two monotypic species: the large hawk-cuckoo (Hierococcyx sparverioides) and the Bock’s hawk-cuckoo or dark hawk-cuckoo (Hierococcyx bocki).”
“These hawk-cuckoos are found in forests from the Himalaya and China to South-East Asia.”
“Hierococcyx sparverioides is the more widespread taxon, breeding widely across montane tropical, subtropical and even temperate mainland Asia and wintering to the south.”
“Hierococcyx bocki ranges in the montane forests of Sundaland.”
“Historically, species delimitation in Hierococcyx cuckoos, as in most other birds, has been guided by plumage differences,” they noted.
“Yet there is only subtle plumage variation across these two species.”
“Since the 1990s, the taxonomy of many tropical and subtropical bird species complexes has undergone a revolution with increasing insights into the importance of bioacoustic characters for species delimitation.”
“Species limits within numerous tropical and subtropical Asian bird species complexes have been re-drawn on the basis of bioacoustic evidence.”
In their new study, Dr. Rheindt and co-authors aimed to investigate the taxonomy of the Hierococcyx sparverioides–Hierococcyx bocki pair and to uncover evidence for cryptic species.
To do this, they used an integrative approach based on bioacoustic, plumage and morphometric data.
They analyzed a total of 107 sound recordings of these two species obtained from online sound libraries.
They also assessed plumage differences and morphometric traits measured on the basis of a series of museum specimens.
Their analysis unearthed a distinct, hit