A group of ornithologists from the National University of Singapore, Bird Tours Asia Ltd., and the University of Queensland has identified a new and enigmatic species of the northern cuckoo, known as Hiero cock. Borneo is a substantial island that is divided among the Malaysian states of Sabah and Sarawak, the Indonesian state of Kalimantan, and the Sultanate of Brunei.
Breeding range map of Hierokokbokki from Sumatra and the Malay Peninsula, Hiero cock sp. from Borneo, and Hierococcus sparbeliodes. Image credit: Ayuwat Jearwattanakanok / Robert O. Hutchinson / James A. Eaton.
Hiero cock is a genus of small birds within the cuckoo family, Cuculinae.
This genus was first recognized in 1845 and currently comprises nine scientifically acknowledged species.
Commonly referred to as hawk cuckoos, they reside in South Asia, Southeast Asia, and East Asia.
“Within the genus A. Hiero cock, the two species maintain strong pair bonds in tropical and subtropical Asia,” stated the lead author, Dr. Frank Reindt from the National University of Singapore and collaborators.
“They are sometimes classified as a single species or recognized as two distinct monotypic species: the big hawk cuckoo (Hierococcus sparbelioides) and the Bockhawk Cuckoo or Darkhawk Cuckoo (Hierokokbokki).
“These hawk-cuckoos inhabit forests that stretch from the Himalayas to China and Southeast Asia.”
“Hierococcus sparbelioides is a more prevalent taxon, extensively breeding across tropical, subtropical, and even temperate mountainous areas of the Asian continent, migrating southward during winter.”
“Hierokokbokki has a range typical of montane forests in Sundaland.”
“Historically, the species boundaries of Hiero cock have largely depended on variations in plumage,” the researchers mentioned.
“Nonetheless, there are only minor differences in the plumage between these two species.”
“Since the 1990s, the taxonomy of numerous tropical and subtropical bird groupings has transformed, driven by a growing understanding of the role of bioacoustic traits in defining species.”
“Species limits for many tropical and subtropical Asian bird complexes have been revisited based on bioacoustic data.”
In a fresh study, Dr. Reindt and co-authors studied the interactions between Hierococcus sparbelioides and Hierokokbokki, unearthing evidence for a newly identified species.
Utilizing an integrated approach that included bioacoustic, plumage, and morphometric data, they analyzed 107 audio recordings of the two species sourced from an online audio library.
They also evaluated differences in plumage and morphometric features by using various museum specimens.
Their findings indicated a previously unnamed population of Hierokokbokki that resides on Borneo, distinguishable primarily by its unique three-syllable main call.
Considering the significant role of vocalizations in cuckoo classification, this population was formally described as a new species: Hierococcyx tiganada.
“The new species from Borneo closely resembles its sibling species, Hierokokbokki, native to Sumatra and Peninsular Malaysia,” the researchers noted.
“Though visually alike, adults of the new species exhibit a slightly grayer mantle, particularly on the upper mantle near the crown, leading to a more subtle contrast between the gray crown and the brownish back relative to Hierokokbokki.”
“The most distinguishing characteristic of these two species lies in the structure of their vocalizations: the new species consistently produces a three-syllable call, while Hierokokbokki produces a two-syllable call.”
“The differences between the new species and Hierococcus sparbelioides reflect the same features that set it apart from Hierokokbokki,” they elaborated.
“Hierococcus sparbelioides also has two-syllable vocalizations.”
“Adult Hierococcus sparbelioides are generally larger, with less dark gray shading near the eyes, a more brownish mantle that contrasts less with the crown, and a pronounced dark red stripe visible against the whitish background of the upper thorax (contrastingly, the new species exhibits a solid red-purple color without stripes).
According to the scientists, Hierococcyx tiganada inhabits mountainous rainforests above 1,000 meters elevation.
“Despite the troubling conservation status of many Southeast Asian avian species reliant on rainforest habitats, the researchers concluded that Hierococcyx tiganada is likely not threatened.”
“Borneo’s lowland rainforests have experienced substantial degradation over the last three decades; however, many montane forests in central Borneo have endured as they remain remote and inaccessible to logging and other extractive practices.”
“Hierococcyx tiganada is relatively well-documented with three known locations in Sabah and an additional site in Sarawak.”
“Records from Kalimantan are notably sparse, and the species does not seem to inhabit the Meratus Mountains of South Kalimantan.”
“Nonetheless, this species likely exists widely across extensive mountainous regions of northern Borneo, often near the borders of Kalimantan, Sarawak, and Sabah; the scarcity of records may indicate insufficient observational coverage beyond established birdwatching locales.”
Hierococcyx tiganada is the first Hiero cock species described in the 20th/21st century.
“This discovery underscores the profound significance of bioacoustic research in biodiversity exploration and further amplifies Borneo’s biogeographical significance,” the authors concluded.
Their study will be published in Asian Ornithology Journal.
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Frank E. Reindt et al. 2025. Discovery of a mysterious new hawk cuckoo species (genus Hiero cock) from Borneo. Asian Ornithology Journal 41:34-43
Source: www.sci.news
