Following a review by the Norfolk Records Committee in July 2020, we have decided to take a two-tiered approach to the acceptance of Siberian Chiffchaff candidates. This will be to either accept as tristis, or to accept as 'showing characteristics of Siberian Chiffchaff/ probable intergrade' (details below).
Identification of Siberian Chiffchaffs has been a subject of much debate over the years, and there are of course many reference papers published that committees and individuals alike can use as guidance for their own processes. Amid the more recent developments, has been the amendment of traditional identification characteristics in line with results of work carried out on mitochondrial DNA (mtDNA), which have suggested that the ‘traditional’ approach may actually be too conservative. Studies have suggested that birds can show varying degrees of yellow and green in the plumage, and also potentially have mixed vocalisations, yet still return a positive mtDNA test result.
We know that Scandinavian Chiffchaff abietinus, and Siberian Chiffchaff tristis, have a zone of overlap in Russia and that the two taxa hybridise. A recent Russian study in this hybrid contact zone took a different approach and studied the nuclear DNA (nDNA) of the birds found there, comparing these results with the birds morphological characteristics and vocalisations. The findings of that paper can be read in the link below:-
https://onlinelibrary.wiley.com/doi/full/10.1002/ece3.2782
We appreciate that this article is heavy going in places, but in summary, birds with tristis mtDNA (so birds that would return a positive test from the lab as a tristis Siberian Chiffchaff based on their mtDNA) could have mixed nDNA – sometimes significantly so. This means they are hybrids with abietinus and have some abietinus nDNA (in some cases up to 40%!). It also means in some cases they had mixed morphological characteristics and mixed vocalisations. While these birds in most cases still had a majority of tristis nDNA, the committee felt that the findings were significant – could such intergrades explain the frequent Siberian Chiffchaff candidates reaching our shores which show lots more green and yellow in the plumage than ‘traditional’ tristis, and mixed call types? Should we be calling these birds tristis when there is a possibility of them having mixed nDNA? Lab tests here focus on mtDNA and so some birds returning positive tests for tristis could still be hybrids.
Based on the submissions received by the committee, it is our opinion that Siberian Chiffchaffs showing typical brown and white plumage, dark bare parts, very reduced green or yellow and typical monosyllabic calls, are rare birds here. We are keen to document those birds properly, but also still document the appearance of birds showing more mixed features as further studies in the future could reveal more and move the goal posts for identification further! It was therefore decided that we would adopt a cautious approach going forward, and accept all future records into two categories.
We urge people to still submit all Siberian Chiffchaff records, so that we can properly document the different types occurring in the county, and will acknowledge all acceptable records of either 'category' with initials. We also cannot stress enough how important we consider sound recordings to be. If you are fortunate enough to come across a Siberian Chiffchaff candidate please try your best to record it. Remember too that you do not need specialist equipment to do this, most mobile phones are perfectly capable of capturing sufficient sound detail even with the voice recorder or video settings.
Our two categories for acceptance will be as follows:-
Siberian Chiffchaff
• Birds that are comprehensively described (and photographed where possible) exhibiting traditional morphological characteristics of tristis.
• Birds sound recorded which exhibit classic call or song.
• Trapped birds which have been mtDNA tested with a positive result for tristis returned, AND conform to traditional morphological characteristics of tristis.
Showing characteristics of Siberian Chiffchaff/probable intergrade
• Birds showing morphological characteristics of tristis but with a sound recording/description which details Common/Scandinavian Chiffchaff call types.
• Birds well described/photographed, which are clearly 'Siberian Chiffchaff' types, but exhibit plumage characteristics that do not conform to traditional tristis, such as excess amounts of green and yellow in the plumage.
• Trapped birds which have been mtDNA tested with a positive result for tristis returned, but do not conform to traditional morphological characteristics of tristis.
So what do we consider the ‘traditional morphological characteristics of tristis’?
• A predominance of brown/buff plumage tones and pale underparts, lacking excessive yellow and green particularly in supercilium, underparts and mantle in normal field views. We accept some green in remiges and scapulars is often present.
• Dark bare parts
• Calls – typical tristis call: a mournful, downslurred, monosyllabic note.
Due to the difficulty of assessing these birds from photos, in any case where we feel the appearance in images or descriptions is not totally clear, and has not been assessed comprehensively in different light conditions, we will take a cautious view.
Norfolk Records Committee, August 2020
Identification of Siberian Chiffchaffs has been a subject of much debate over the years, and there are of course many reference papers published that committees and individuals alike can use as guidance for their own processes. Amid the more recent developments, has been the amendment of traditional identification characteristics in line with results of work carried out on mitochondrial DNA (mtDNA), which have suggested that the ‘traditional’ approach may actually be too conservative. Studies have suggested that birds can show varying degrees of yellow and green in the plumage, and also potentially have mixed vocalisations, yet still return a positive mtDNA test result.
We know that Scandinavian Chiffchaff abietinus, and Siberian Chiffchaff tristis, have a zone of overlap in Russia and that the two taxa hybridise. A recent Russian study in this hybrid contact zone took a different approach and studied the nuclear DNA (nDNA) of the birds found there, comparing these results with the birds morphological characteristics and vocalisations. The findings of that paper can be read in the link below:-
https://onlinelibrary.wiley.com/doi/full/10.1002/ece3.2782
We appreciate that this article is heavy going in places, but in summary, birds with tristis mtDNA (so birds that would return a positive test from the lab as a tristis Siberian Chiffchaff based on their mtDNA) could have mixed nDNA – sometimes significantly so. This means they are hybrids with abietinus and have some abietinus nDNA (in some cases up to 40%!). It also means in some cases they had mixed morphological characteristics and mixed vocalisations. While these birds in most cases still had a majority of tristis nDNA, the committee felt that the findings were significant – could such intergrades explain the frequent Siberian Chiffchaff candidates reaching our shores which show lots more green and yellow in the plumage than ‘traditional’ tristis, and mixed call types? Should we be calling these birds tristis when there is a possibility of them having mixed nDNA? Lab tests here focus on mtDNA and so some birds returning positive tests for tristis could still be hybrids.
Based on the submissions received by the committee, it is our opinion that Siberian Chiffchaffs showing typical brown and white plumage, dark bare parts, very reduced green or yellow and typical monosyllabic calls, are rare birds here. We are keen to document those birds properly, but also still document the appearance of birds showing more mixed features as further studies in the future could reveal more and move the goal posts for identification further! It was therefore decided that we would adopt a cautious approach going forward, and accept all future records into two categories.
We urge people to still submit all Siberian Chiffchaff records, so that we can properly document the different types occurring in the county, and will acknowledge all acceptable records of either 'category' with initials. We also cannot stress enough how important we consider sound recordings to be. If you are fortunate enough to come across a Siberian Chiffchaff candidate please try your best to record it. Remember too that you do not need specialist equipment to do this, most mobile phones are perfectly capable of capturing sufficient sound detail even with the voice recorder or video settings.
Our two categories for acceptance will be as follows:-
Siberian Chiffchaff
• Birds that are comprehensively described (and photographed where possible) exhibiting traditional morphological characteristics of tristis.
• Birds sound recorded which exhibit classic call or song.
• Trapped birds which have been mtDNA tested with a positive result for tristis returned, AND conform to traditional morphological characteristics of tristis.
Showing characteristics of Siberian Chiffchaff/probable intergrade
• Birds showing morphological characteristics of tristis but with a sound recording/description which details Common/Scandinavian Chiffchaff call types.
• Birds well described/photographed, which are clearly 'Siberian Chiffchaff' types, but exhibit plumage characteristics that do not conform to traditional tristis, such as excess amounts of green and yellow in the plumage.
• Trapped birds which have been mtDNA tested with a positive result for tristis returned, but do not conform to traditional morphological characteristics of tristis.
So what do we consider the ‘traditional morphological characteristics of tristis’?
• A predominance of brown/buff plumage tones and pale underparts, lacking excessive yellow and green particularly in supercilium, underparts and mantle in normal field views. We accept some green in remiges and scapulars is often present.
• Dark bare parts
• Calls – typical tristis call: a mournful, downslurred, monosyllabic note.
Due to the difficulty of assessing these birds from photos, in any case where we feel the appearance in images or descriptions is not totally clear, and has not been assessed comprehensively in different light conditions, we will take a cautious view.
Norfolk Records Committee, August 2020
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