Centropus chalybeus (Salvadori, 1876)

Bishop, K. David, 2023, The avifauna of Biak Island, Papua, Indonesia with comments on status, conservation, natural history and taxonomy, Bulletin of the British Ornithologists’ Club 143 (1), pp. 3-62 : 27

BIAK COUCAL Centropus chalybeus # RR, Near Threatened

Local name Man Sow Sow (Sansundi, Kuneff).

Range Biak, Supiori.

Status Endemic species. Rand & Gilliard (1967) speculated that it may also occur on Numfor but, despite several birders having visited the latter recently, the species has not been found there suggesting that it is endemic to Biak. Generally inconspicuous except when vocalising. July 1982: KDB found the species noticeably commoner on Supiori than Biak, but just as inconspicuous. He observed two in forest below 60 m. The first clambered up a vine-covered tree at the edge of a treefall clearing 5 m from the Wandei River . The second bird was also perched in a dense vine-covered tree 5 m above ground, c. 10 m from a dry creek. Even when it moved further into the canopy it remained silent, but calling birds were heard up to c. 300 m.

Voice A low, resonant, hollow, hooting call, comprising a single note repeated over and over, ascending and descending in waves. KDB has also recorded chalybeus counter-singing. Although a close relationship to its presumed sister species, Greater Black Coucal C. menbeki , is indicated by mtDNA (Sorenson & Payne 2005), their vocalisations differ markedly. The song of chalybeus is a series of identical upslurred notes repeated at varying speeds, but that of menbeki comprises ‘low-pitched, resonant, far-carrying, booming hoots, given in a slow and cadenced series that descends in pitch’ ( Pratt & Beehler 2015). The call of chalybeus is a ‘gruff cough that turns into a decelerating chatter’ ( Gregory 2017; KDB tapes) whereas menbeki utters a guttural series of dry, rattled notes that rise in pitch ( Pratt & Beehler 2015). Woxvold & Bishop (2020) provided sound-recordings of a variety of calls.