Evidence from citizen science and museum specimens suggests species rank for Erythrogenys [erythrogenys] imberbis (Salvadori, 1889), ‘Red-eyed Scimitar Babbler’

Summary. Rusty-cheeked Scimitar Babbler Erythrogenys erythrogenys (Vigors, 1832) comprises two subspecies in the Himalaya (nominate and ferrugilata) and two more, disjunctly (with Spot-breasted Scimitar Babbler E. mcclellandi interposing), in Myanmar and Thailand (imberbis and celata). Prompted by the observation that these two populations appear to exhibit differences in eye colour, we use citizen science data (343 online photographs and >100 sound-recordings) and 66 museum specimens to evaluate potential differences in bare-part and plumage colour, morphometrics and vocalisations. We find that Thai-Burmese birds are distinguished from their Himalayan counterparts by their red vs. white irides, dark vs. pale bills, browner ear-coverts, typically grey vs. whitish lores and the absence of a white submoustachial spot. They also less frequently have white flecks on the eye-rim and are, on average, less heavily streaked on the breast. Thai-Burmese birds are further characterised by their smaller size with significantly shorter wings and tail, and divergent voice of females in duet (a mellow peew and burry prreew vs. a staccato pip!). Cumulatively these multiple differences, fully consistent in iris colour, size and female voice, and highly indicative in other features, point to a more appropriate treatment of the Thai-Burmese birds as a species, Red-eyed Scimitar Babbler Erythrogenys imberbis (Salvadori, 1889).