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IDENTIFICATION OF SIBERIAN CHIFFCHAFF – Phylloscopus (collybita) tristis
From late September one can expect to find Siberian Chiffchaff – Phylloscopus (collybita) tristis in the Netherlands. Most are seen in October and some will stay for the winter. They are noticed because of a pale buffy or greyish appearance and/or by a unique ‘unhappy’ sounding monotone ‘peep’ call. It’s not a real rarity like Pallas’ Leaf Warbler, but it’s a bit less common compared to Yellow-Browed Leaf Warbler. The thing is that they are way overlooked and hopefully this blog can contribute to some change
What is ‘tristis’
Dutch birders follow strict rules when identifying tristis. The bird must be sound recorded when calling its classic monotone call, or singing its seldomly heard song. Birds that only give away ‘alternative’ calls could be hybrids and birds that sing a mixture of tristis and Common Chiffchaff –Phylloscopus collybita song could even be other taxa that imitate tristis. We also used to disqualify all tristis-like birds which showed any hint of green or yellow present in their mantle, head and underparts. These birds were attributed to the Scandinavian subspecies of Common Chiffchaff –Phylloscopus collybita abietinus or perhaps ty the hybrid form ‘fulvescens’. As far as we now know, these aberrant birds are however pure tristis, because they appear to make the right sounds and are the owners of the right DNA. Abietinus is probably inseparable in the field from collybita and its DNA has not yet been found in the Netherlands. ‘Fulvescens’ is probably just the name of all variant birds of the pure tristis population. Much is still unclear about the occurrence of hybridization and sound imitating by chiffchaffs, so it’s hard to decide which field marks are strong enough for a positive identification. DNA investigation on ‘chiffies’ is still running in the Netherlands this winter, so hopefully we can get to some more pieces of the puzzle soon.
As mentioned before, a recording of the right sound is needed for positive identification (when DNA is not gathered). A recorded call can be showed in sonogram and tells more than a thousand words. The graph of the classic tristis call shows us a more or less horizontal bar. Every chiffchaff that gives us a call that clearly changes in frequency, can’t safely exclude something other than tristis. A classic collybita sounds clearly two-toned, but many birds utter alternative calls that to the ear sound pretty much monotone, although they never sound like the almost Bullfinch-like unhappy call of tristis (which means ‘sad’ in latin). It’s a fact that pure tristis can also call alternatively, especially in younger still practicing birds. There are strong clues that those calls can in many cases still be differentiated from the sometimes less clearly two toned alternatives calls of collybita, by showing a more rounded instead of somewhat pointy ‘roof’ in their inverted-‘V’-shaped sonogram. If heard singing, tristis reminds a bit of a stuttering Willow Warbler, so again much different in sound compared to collybita. Listen for yourself:
This song is recorded by Arend Wassink. But be careful for mixed singers, which mix collybita and tristis elements in their song and could possibly be hybrids. Check this recording of a classic call by Krzysztof Deoniziak.
If browsing on the web it’s clear that a call as ‘flat’ in sonogram as this is hard to be found. Many recorded calls are that aberrant, they wouldn’t survive the strict Dutch criteria. However, It isn’t a problem if the ending of the call bends down in frequency a little bit, making it sound even more ‘sadly’.
The picture by Vincent van der Spek in top of this article tells it all. Classic tristis are pale birds compared to collybita and mostly lack any green on the upperparts. Yellow is mostly restricted to the underwing. Also the lesser underwing coverts are yellowish, which can sometimes be seen sticking out below the bend of the wing and could easily be mistaken with the group of feathers belonging to the flank of a bird. Collybita always shows some green or yellow when being watched closely and in good light conditions. They can show some grey coloring on head and neck, but never that much as classic tristis does. The problem is that tristis knows many variety, with most ‘aberrant’ birds showing green tones in mantle. Some even have some yellow at the eyebrow (especially in front of the eye). It’s not clear where the exact plumage boundaries lie between such birds and other taxa or hybrids between them. Before we get depressed, let’s talk about the easy ones again. Roughly said, classic tristis replaces all green and yellow showed by collybita at underparts, mantle and head, by a nice buff coloring. This coloring will pop up spontaneously when the otherwise cold and grey looking bird gets some bright sunlight. Especially the ear coverts show a highly indicative (and may be diagnostic?) "tobacco" colored patch, which can look almost orangey or pinkish in some light conditions. The rest of the plumage sometimes reminds me of that of Booted Warbler, being tea-with-milk type buff colored. The ‘Booted-effect’ is supported by the noticeably bright eyebrow (even behind the eye), sometimes with some dark edging just above the eyebrow and the very whitish belly, compared to the more uniform looking collybia. A tristis can also be very reminiscent of (Eastern) Bonelli’s Warbler, when seeing a grey bird with contrasting green primaries and tail and a white belly.
Conclusion: classic tristis makes a unique bird in both looks and sounds!
Post by Maarten Wielstra
Many thanks to the photographers and Vincent van der Spek, Nina Olivari and Menno van Duijn for their comments on a concept version of this little article.