In Beijing in winter we are blessed with good numbers of East Asian thrushes… In my experience NAUMANN’S (Turdus naumanni) is the most common, followed by RED-THROATED (Turdus ruficollis) and DUSKY (Turdus eunomus) with BLACK-THROATED (Turdus atrogularis) being the most scarce. It is not uncommon to encounter intergrades, and birds exhibiting features of both NAUMANN’S and DUSKY are frequently encountered (see images at the end of this post). It is much less common to find birds showing features of both Red-throated and Black-throated. However, that is exactly what I found on Sunday at Lingshan.
Unfortunately I wasn’t able to capture many (any!) good quality photographs but the two I did manage (above) show the unusually-marked throat and upper breast. A ‘pure’ Red-throated should show reddish orange marks only on the throat and breast with no black. And Black-throated should show only black or grey markings here, lacking any reddish tones. This bird clearly shows a mixture, with black dominating the lower part of the throat-patch and red dominating the upper part and the neck surrounds. I have never seen a bird like this before but it seems reasonable to assume that this is an intergrade between RED-THROATED and BLACK-THROATED. Although Red x Black-throated Thrushes are rare in Beijing, they are fairly frequent in Central Asia – see here for some information from Kazakhstan.
Vagrant East Asian thrushes, especially first year birds, still cause some identification problems in Europe (e.g. the 2013 Dusky Thrush at Margate in the UK and the recent putative Red-throated Thrush in Finland). This is because we don’t know for sure the variability of ‘pure’ birds, complicated by the fact that we know they interbreed. If we are to improve our knowledge, studies must be made on the breeding grounds, away from areas of potential interbreeding, so that we can better understand natural variation of pure species and pin down the tell-tale signs of intergradation. Although birders in Beijing and East Asia have a lot of experience of these thrushes, because we see these birds on the wintering grounds, in some cases we cannot be certain whether or not we are looking at pure birds or intergrades.. This means we are not best-placed to provide anything other than opinions about what we *think* are signs of intergradation based on seeing hundreds, and in some cases, thousands of these beautiful thrushes.
That said, I think we can all agree that the Lingshan bird is an intergrade. And what a cracker it was!
Just for interest, here are a couple of apparent DUSKY x NAUMANN’S THRUSHES from Beijing.