Distinctive; previously considered closest to O. ruficeps, but molecular data place it as sister to O. frontalis#R. For some time there was much confusion over names of present species, O. ruficeps and O. sepium; consequently, some statements in recent literature require reconfirmation. Proposed race nuntius (Cagayan Sulu, Philippines) included in nominate; however, population of Palawan, which has never been named, has proved genetically distinct, to point where (in one opinion) slightest phenotypic difference would be considered sufficient to carry it to species rank#R (comparison of voices reveals no obvious differences, but targeted sampling might reveal subtle or average distinctions). Three subspecies recognized.
Food and feeding
Status and conservation
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