Hybrid Black-throated x Naumann’s Thrush at Pui O, Lantau on 7th November 2009
Michael R. Leven (on behalf of the Records Committee)
Introduction
http://www.hkbws.org.hk/BBS/view ... mp;highlight=Thrush
A thrush was photographed at Pui O on 7th November by Vivian Cheung (see link above) and XinTian Yu (from Shenzhen - see below). It was initially identified from photographs as Black-throated Thrush
Turdus atrogularis, but it was soon noted that it showed some red colouration in the tail, suggesting that it might be a hybrid between Black-throated Thush and Red-throated Thrush
T. ruficollis. Subsequently, John Allcock drew attention to Moores (2002) and suggested that the bird might be a hybrid between
T. atrogularis and Naumann’s Thush
T. naumanni due to the extensive rufous mottling/spotting on the flanks. Though this last feature is reasonably apparent in the last of the three photos in the original post (below), it is more apparent in a photo submitted by Xin Tian Yu:
Discussion
The closely related group of thrushes comprising Black-throated, Red-throated, Dusky and Naumann’s Thrushes (
Turdus atrogularis,
T. ruficollis,
T. eunomus and
T. naumanni) has at various times been treated as one polytypic species (e.g. Portenko 1981); and as two species, Dark-throated Thrush (containing the taxa
atrogularis and
ruficollis) and Dusky Thrush (containing the taxa
eunomus and
naumanni) (e.g. Vaurie 1959); but is now treated as four species by the International Ornithological Congress (IOC) the authority followed for the Hong Kong List. Despite this taxonomic treatment, it is recognised that hybrids are relatively frequent: Clement and Hathaway (2000) illustrated hybrids between
atrogularis and
ruficollis and between
eunomus and
naumanni, and described (from Portenko 1981) hybrids between both
atrogularis and
ruficollis with
naumanni.
The Pui O bird is clearly a hybrid of at least two of these species, as, of this group, only
atrogularis has a black(ish) throat, and
atrogularis has no rufous colouration in the tail. Thus, it must be a hybrid between
atrogularis and either
ruficollis or
naumanni (or both, as it need not be a F1 hybrid). (A hybrid with
eunomus is perhaps theoretically possible but unlikely as the bird shows no features of this taxon.)
Assuming that a hybrid would most likely exhibit features of a parent and not features of another taxon, the key issue is the difference in pattern and extent of flank and undertail covert streaking and spotting between
ruficollis and
naumanni, with this being much more extensive in the latter taxon (Moores 2002). On this basis, this bird must be an
atrogularis/naumanni hybrid: as was shown by Moores, the spotting on the flanks is too heavy and extensive for
ruficollis.
Accordingly, this record has been accepted by the Records Committee as ‘a bird showing the features of a hybrid between
T. naumanni and
T. atrogularis’.
Acknowledgements
The Records Committee wishes to thank the original observers and all those who contributed to the discussion of this record, in particular John Allcock who first suggested that the bird was a
atrogularis/naumanni hybrid.
References
Clement, P. and Hathaway, R. 2000. Thrushes. Christopher Helm, London.
Moores, N. 2002.
Probable hybrid Red-throated Thrush Turdus ruficollis ruficollis and Naumann’s Thrush Turdus naumanni naumanni.
http://www.birdskorea.org/Birds/Identification/ID_Notes/BK-ID-Thrush.shtml
Portenko, L.A. 1981. Geographical variation in Dark-throated Thrushes (Turdus ruficollis Pallas) and its taxonomical value.
Proc. Zool. Inst. Acad. Sci. USSR 102: 72-109.
Vaurie, C. 1959.
Birds of the Palearctic fauna: passerines. Witherby, London.
[
Last edited by cgeoff at 18/07/2010 16:16 ]
