Watch out for the Russians!
Bijgewerkt: 15 mrt 2020
Recently, a British rarity committee member asked how we deal with ‘Russian Jackdaws’ (ssp. soemmerringii) in the Netherlands. Incredibly, a day later I saw my best candidate in years. I didn’t have any birding equipment on me, so I had to use my phone to photograph it.
The commonly accepted (assumed?) situation in the Netherlands is that the dark ssp. spermologus is common year round*, that ‘Nordic Jackdaw’ (ssp. monedula) is a migrant and winterer (proven by rings) and that 'Russian Jackdaw' (soemmerringii) is a (very) scarce winterer.
ID challenges The problem is that Jackdaw variation is clinal and the ID is often problematic. There are intergration zones in Eastern Europe, and there's huge individual variation within populations (e.g. only half of the Russian Jackdaws have these long white neck marks; Shirihai & Svensson, 2018). So the dividing line between some individual Nordic and Russian Jackdaws is thin – very thin.
The best sources on the matter are probably Offereins (2003) and HWBP (Shirihai & Svensson, 2018), though they are confusingly contradicting at times. More on that later.
A week later I returned to the site prepared. I conquered the storm and the dark clouds and managed to see the bird for a whole 3 minutes before it was flushed by a dog. It looked so dark, with the white in the neck so prominent, that I figured it was a Russian. Ok, I made some critical remarks, but still: I was too quick on the draw...
The return #2
A couple of days later I went back once more to observe and photograph it in better light conditions. I quickly found the bird. And the doubts kicked in immediately.
There are no moult limits, so this is an adult. But this is of no use for the ID. At least in soemmerringii the amount of white in the neck is not age-related (Shirihai & Svensson, 2018).
Overall the bird looked much greyer than during the dark weather earlier that week. Shoot! On a wanderer from the east I want to see nearly black underparts, as described by Offereins (2003) for 'classic' (extreme?) Russians. Contradiction #1: Shirihai and Svensson (2018) don't mention this. They even write: "[soemmerringii] has dark grey rather than near-black underparts (thus close to monedula)." ??? Confusing!
The underparts were more mottled than I noted before (one of my initial 'critical remarks'): a 'Nordic' feature according to Offereins (2003). Contradiction #2: again this is not mentioned by Shirihai & Svensson (2018).
Intriguingly a bird from Finland credited as a presumed soemmerrengii in HWPB looks pretty similar. Its ID is based on the 'slightly paler grey on head' and 'distinctly whiter half collar'. But Shirihai & Svensson (2018) also add: "much individual variation, and extremes of monedula can be very similar".
It's indeed not dissimilar to birds I've seen in soemmerringii country. Check this one from SE Bulgaria (2011) and note the similarity of the grey and - yes - strongly mottled underparts. The main difference is that the Bulgarian bird has somewhat scalloped upperparts - a feature Shirihai & Svensson (2018) do and Offereins doesn't mention for Russian. And in fact it has a somewhat less white collar:
So my bird definitely wouldn't stand out as something odd within the breeding range of soemmerringii. But a more prominently marked Nordic cannot be excluded, not on current knowledge anyway, and since these are default the tentative ID should probably be: presumed (extreme?) Nordic / possible Russian.
Now what? The two sources mentioned above fully acknowledge the problematic ID (cline, integration, individual variation). They are contradicting on some points. The thing is: pics in these articles are mainly from wintering birds, which IMHO makes their ID rather tentative. So who's gonna make 100s of shots of soemmerringii wintering within within their eastern breeding ranges?
* PS Please note that Shirihai & Svensson (2018) mention that Dutch birds are probably best included in monedula instead of spermologus. However, a pic from Holland in the species account is nonetheless labelled as spermologus! It only adds to the confusion and probably perfectly reflects the clinal variation.
Offereins, R. 2003. Identification of eastern subspecies of Western Jackdaw and occurrence in the Netherlands. Dutch Birding 25: 209-220
Shirihai, H. & L. Svensson. 2018. Handbook of Western Palearctic Birds. Helm, London.