Background Taxonomic treatment of the Zoothera dauma species complex is highly variable and has been hampered by the absence of song recordings for the Nilgiri Thrush (Zoothera aurea neilgherriensis).
Methods I obtained two recordings of the song of neigherriensis from southern Indian. Here I publish sonograms and analyze song recordings for all but one currently described taxon from the Eurasian portion of the geographic range of this species complex. Principal component analyses were used to investigate song differences between taxa
Results The song of neigherriensis is a highly complex series of strophes remarkably similar to the song of the insular Zoothera major. Vocal analyses across the complex indicate four key groups of taxa differentiated in their songs: (1) simple flat whistled songs which include the northern aurea, toratugumi and the undescribed Taiwan population; (2) eastern populations of dauma (reported here for the first time) which sing like northern birds but with much broader bandwidth, (3) strongly down-slurred, thin whistles of tropical resident imbricata of Sri Lanka and horsfieldi of Indonesia, and (4) highly complex songs of Himalayan dauma, neilgherriensis and major.
Conclusions Zoothera dauma is unlikely to represent a single species given the simple singing populations from its eastern range and highly complex song from the Himalayan portion of its range. neilgherriensis should either be transferred from Zoothera aurea, where it is currently classified as a subspecies, and be placed as a subspecies within Z. dauma from the Himalayas or it should be recognized as a distinct species. Given the small number of songs available for analyses, I suggest the former course until it can be clearly demonstrated that neilgherriensis and Himalayan dauma are vocally distinct.
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