Dusky Thrush ruminations

Pure birds, intergrades (and they all look pretty smart anyhow!)

by Martin G. with photos by Lee Dingain (Almost Birding)

I was birding with Mark Thomas, on his ‘patch’ at Buckton, East Yorkshire on the morning many were at, or heading to Margate, Kent to see the reported Dusky Thrush. We had seen early photos of the bird and were interested in the bird’s appearance. Up came the subject of a 2nd cal year female Black-throated Thrush which Mark had found, at Buckton (what a patch!) in March 2007. That bird, which I saw very well but failed to photo as well (see here!) had an unusually striking pale supercilium (for a Black-throated). Mark mention than it had been suggested to him that his bird was not ‘pure’. We talked about how, in profile at least, the Margate bird didn’t look that different to the Buckton Black-throated. Ruminations.

Lots of new pics of the Margate bird soon appeared:

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But the concerns didn’t go away with them. There were clearly some dull reddish tones on the breast sides and the flanks had a peculiar Black-throated feel, as already discussed. And where were the dark feathers centres to the upperparts expected in an ‘easy Dusky’? These were just ruminations. I simple don’t know enough about variation in 2cy Duskies to make definitive statement.- so tweeted the key question on my mind- “was it pure?”. It wasn’t the most popular ‘tweet’ I have ever posted : ). I certainly wasn’t the only one with questions however and Alan Tilmouth and Terry Townshend were very helpful with news and views.

Thoughts from Asia

So I’ve said my bit. Would like to know the variation in appearance of young 2cy female Dusky Thrushes from the ‘core range’. Meanwhile  a few thoughts from a few who know a lot more than me, (and they are very cool birds anyway!). Special thanks to Terry T.

“Based on shots forwarded to me I think it is an intergrade.”
Jesper Hornskov (Beijing-based Danish birder and tour leader with over 20 years China experience)
.
“..boasting both dark brown- and rufous-centred feathers on its underparts the Margate bird is definitely a Dusky-Naumann’s intergrade. Such intergrades (or hybrids if you treat the two, as is increasingly the case, as separate species) are pretty common in east Asia with perhaps as many as 10-15% of the birds that I see in Beijing showing mixed characters.”
Paul Holt, Beijing-based birder and tour leader with Sunbird
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Hi Martin,
 As you probably know, we seldom get to see many Duskys here as late as Mid-May, so I have much less experience of them so late in spring than eg between Oct-April. Naumann’s and intergrades too have gone though by late April. The Surfbirds thrush looks odder in some images than in others. You might be right, but I am not so sure of structure – seems to be fair amount of variation in Dusky etc I think the pallor of the bird on the upperparts too is okay for Dusky at this time of year – and it does show some darker markings eg on the scaps (as in 2 of the Duskys here this past week). The only obviously odd features for me appear to be (1) the warmth of the markings on the breast sides and (2) the streaky look to the lower flanks. Some Duskys do show such warmth on the breast sides (chestnutty, not rufous), as do most (all?) hybrids with Naumann’s (so this could be a 2nd generation hybrid or..?). Streakiness of markings on the lower flanks is much less usual, and as you know this latter feature might well hint at some possible hybrid influence from one of the “dark-throated” thrushes.
So – either a very odd 2cy Dusky or a slightly odd 2cy “Dusky plus [intergrade]”.
Very best wishes to you and yours,
Nial Moores (Birds Korea)
Dusky/Naumman’s hybrids (or intergrades) are relatively common with around 10-15% of the birds seen in Beijing said to be intergrades (this is supported by my own observations since 2010). Of course, these birds go on to breed with one or the other, too, leading to all sorts of mixes with varying degrees of Dusky and Naumann’s genes.

I believe Black-throated intergrades are much more unusual. I have only seen two intergrades (of Black-throated x Red-throated) which, one would assume, would be more likely to occur than Black- or Red-throated x Dusky or Naumann’s. But I guess much would depend on the breeding ranges, about which I am unsure.
Hope that helps…
.
Terry Townshend (Birding Beijing and on Birding Frontiers team)
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Thanks especially to Lee Dingain of Almost Birding for use if his wonderful images of the Margate Thrush

More fine images on Josh Jones’ Blog

6 thoughts on “Dusky Thrush ruminations

  1. julianhough

    I haven’t seen Dusky Thrush for many years, but the presence of those warm feathers in the underparts would seem to point towards a naumanni influence? Not sure what amount, if any, Duskies can show, but how would you separate variation from intergradation??
    I remember this question coming up years ago when Paul Holt and I were birding together in China and referencing photos of the accepted 1975 (?) Shetland bird; he thought it might be a male intergrade since the photos, as I recall from memory, show some rufous admixed into the flanks. Not sure if that was ever revisited?

    Reply
  2. Ian Fisher

    Hi Martin,

    I have just looked at my photographs of Dusky Thrush from late Feb/early March 2009 from Japan. Many show ‘warmer’ feathers in the underparts but then others do not! Perhaps hybrids are more common than we think?

    Reply
    1. Martin Garner

      Hi Mark, I can see how it might look like I took an ‘angle’ however you consider me to be more cunning than in reality! Alan Tilmouth offered to ask Terry Townshend what he thought who in turn contacted Paul and Jesper. Charlie Moores simultaneously suggested I contact his brother Nial. I would have published their responses whatever they were, as they had made the effort. Delay was due to 2 weeks in Shetland, no time and rubbish internet. The fact that they all came to roughly similar conclusion was just how it played out. I did see LS’s comments but they are already in the public domain. I admit his comments though do still leave me with questions…

      Reply
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