SARBN: of impossible gulls...
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Trevor Hardaker
Oct 18, 2017, 3:43:54 AM10/18/17
to SA Rare Bird News
One thing I have learnt over the last few days is that the identification of large gulls is far from straightforward… in fact, it is incredibly confusing and still has much to be resolved!!
When studying the wing patterns of these gulls, one realises that there is much variation in terms of the upper- and underwing patterns within species across the different populations of those species and that no field guide / dedicated advanced ID guide covers all of these variations adequately. I have been discussing the gull at Walvis Bay with several highly experienced European and Asian birders over the last few days, many of them from the Gull Research Organisation (www.gull-research.org), who are working on trying to get to the bottom of large gull ID criteria by documenting in incredible detail various individuals of known species and formulating a list of criteria that can be safely used to separate out the various species.
To this end, it would seem that they feel that the Walvis Bay bird is possibly not a Yellow-legged Gull. Apparently, in terms of the wing pattern, the combination of a large mirror on P10, a medium sized mirror on P9, a rather thin medial black band on P8, a small black dot on P4 and a long, pale tongue on the underside of P10 is very rare, if not unknown, in Yellow-legged Gull. They also feel that the apparent slim and attenuated shape of the bird, together with the more upright stance, is not typical of Yellow-legged Gull and is more reminiscent of birds of a central Asian origin.
They are suggesting that the combination of features visible on the wing pattern as well as the shape would fit better with the forms that are breeding in the steppes of south-western Siberia which is a transition zone between Caspian Gull (Larus cachinnans) and Steppe Gull (Larus fuscus barabensis). The birds that are breeding in this region do not tie in neatly with their understanding of what either of those species can look like at the moment and it is unknown whether they are extreme variations of either Caspian or Steppe Gulls or whether they are perhaps hybrids between the two species. Much more research is required on these birds before they can safely say what they actually are and this will probably not only involve visual research to accurately document the range of features these forms show, but also DNA analyses to see what they are actually dealing with here.
Whatever the case, for the foreseeable future, I will continue to post updates on our bird and just refer to it as the WALVIS GULL until we have any further information on it. It may be a while though until we know what we actually have in Walvis Bay so, for those who have seen it, it is probably one that you will just have to put into your back pocket for now and hopefully bring out to add to your list at some future stage once we actually know what it is… on that same note, if anyone is there and happens to see the bird drop a feather or two, please do try and collect those and perhaps we can try and get our own DNA analysis underway to see if we can get to any answers on this one.
I am indebted to Lou Bertalan, Mars Muuse, Alex Boldrini, Peter Adriaens, Amir Ben Dov, Xrysostomos Bairaktaris, Michalis Dretakis, Karl Hammar and Jan Jorgensen who all provided valuable input and photos for ID discussion purposes on our rather interesting and confusing bird!
We’ve had a few “head scratchers” turning up in Southern Africa of late that have really pushed us to dig deep to resolve the identification of those birds, so let’s hope that the next mega is more of a “paint by numbers” type of bird, because I’m not sure how much more of this my poor little brain can handle…😉
Kind regards
Trevor
When studying the wing patterns of these gulls, one realises that there is much variation in terms of the upper- and underwing patterns within species across the different populations of those species and that no field guide / dedicated advanced ID guide covers all of these variations adequately. I have been discussing the gull at Walvis Bay with several highly experienced European and Asian birders over the last few days, many of them from the Gull Research Organisation (www.gull-research.org), who are working on trying to get to the bottom of large gull ID criteria by documenting in incredible detail various individuals of known species and formulating a list of criteria that can be safely used to separate out the various species.
To this end, it would seem that they feel that the Walvis Bay bird is possibly not a Yellow-legged Gull. Apparently, in terms of the wing pattern, the combination of a large mirror on P10, a medium sized mirror on P9, a rather thin medial black band on P8, a small black dot on P4 and a long, pale tongue on the underside of P10 is very rare, if not unknown, in Yellow-legged Gull. They also feel that the apparent slim and attenuated shape of the bird, together with the more upright stance, is not typical of Yellow-legged Gull and is more reminiscent of birds of a central Asian origin.
They are suggesting that the combination of features visible on the wing pattern as well as the shape would fit better with the forms that are breeding in the steppes of south-western Siberia which is a transition zone between Caspian Gull (Larus cachinnans) and Steppe Gull (Larus fuscus barabensis). The birds that are breeding in this region do not tie in neatly with their understanding of what either of those species can look like at the moment and it is unknown whether they are extreme variations of either Caspian or Steppe Gulls or whether they are perhaps hybrids between the two species. Much more research is required on these birds before they can safely say what they actually are and this will probably not only involve visual research to accurately document the range of features these forms show, but also DNA analyses to see what they are actually dealing with here.
Whatever the case, for the foreseeable future, I will continue to post updates on our bird and just refer to it as the WALVIS GULL until we have any further information on it. It may be a while though until we know what we actually have in Walvis Bay so, for those who have seen it, it is probably one that you will just have to put into your back pocket for now and hopefully bring out to add to your list at some future stage once we actually know what it is… on that same note, if anyone is there and happens to see the bird drop a feather or two, please do try and collect those and perhaps we can try and get our own DNA analysis underway to see if we can get to any answers on this one.
I am indebted to Lou Bertalan, Mars Muuse, Alex Boldrini, Peter Adriaens, Amir Ben Dov, Xrysostomos Bairaktaris, Michalis Dretakis, Karl Hammar and Jan Jorgensen who all provided valuable input and photos for ID discussion purposes on our rather interesting and confusing bird!
We’ve had a few “head scratchers” turning up in Southern Africa of late that have really pushed us to dig deep to resolve the identification of those birds, so let’s hope that the next mega is more of a “paint by numbers” type of bird, because I’m not sure how much more of this my poor little brain can handle…😉
Kind regards
Trevor
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