Rück’s Blue-flycatcher Cyornis ruckii: the evidence revisited

Nigel Collar (BirdLife International, Pembroke Street, Cambridge CB2 3QZ, UK)

KUKILA
Vol. 23 (2020)

Photographs and measurements of all four known specimens of Cyornis ruckii are provided. One of the two adult males has the underparts entirely blue, the other has the lower belly and vent greyish-white; a widely available illustration shows far too much white on the underparts. Contrary to speculation, the specimens are not aberrant Pale Blue Flycatchers C. unicolor. Review of early texts reveals that no locality was ever given for the first two specimens and that the second two, from near Medan, Sumatra, were almost certainly taken in primary forest, not exploited forest as currently stated. Searches should target primary lowland forest in northern Sumatra.