| Summary: | Crested Argus Rheinardia ocellata has two highly disjunct populations in Vietnam and Lao PDR (nominate ocellata) and Malaysia (subspecies nigrescens). When evidence from the small sample of museum specimens is supplemented by novel photographic and acoustic evidence, Malaysian nigrescens proves to be distinct on a suite of characters: yellower bill with blackish nares, buffier supercilium, throat and breast, different-coloured and -structured crest, different-patterned upperparts and tail, a purer, more fluent, longer, lower Short Call (used by advertising males), markedly divergent from the explosive, nasal, double-noted equivalent in nominate ocellata, and a higher number of loud notes in the Long Call including an unexplained bimodal vs. unimodal pattern (hence either average 8.6 or 14.5 vs. 7.1 loud notes per call). In combination these characters indicate a level of differentiation compatible with species rank for nigrescens, and this is strongly reflected in Tobias criteria scoring. The conservation of the two forms requires urgent reconsideration.
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