Monday, 23 March 2009

Show Us Yer Passport

I took the kids to see some Spring Lambs this morning, gambling about in the fields in a strong Northerly wind all spindly-legged and jumping enthusiastically just pleased to be alive. It's important that you know that this was why I was parked looking at fields at the North west corner of Ashington, to watch Lambs with my kids.

I get bored with farm animals quite quickly, I accept this. My only diversion was Jackdaws, so I did what you all would have done in my circumstances, I started checking the Jackdaws for individuals showing the characteristics of monedula, that's the nominate form from Scandinavia in English (ours are spermologus), within a few minutes I've picked out an individual that has a strong contrast between the pale silvery grey cheeks and neck and the rest of the underparts and it's got a very noticeable white half collar line.
Once again as often happens it dawns on me that I haven't got a clue what I'm looking for, I have this vague notion that the white collar line indicates monedula but are there are other features I should be looking for? I spent a few minutes comparing this individual with some of the others present and the only other notable features appeared to be slightly lighter grey underparts contrasting with darker wings and some 'scalloping' on the underparts or pale fringes.
So now I have a dilemma, do I get home and sort out the jobs my wife left for me or do I spend the rest of the day researching the racial differences in Eurasian Jackdaw?
Of course I did the right thing as I'm sure most of you would although I may fail to convince Ash when she gets home that understanding the finer points of Jackdaw identification is as important as having something to wear tomorrow that isn't creased.
I started with Collins and quickly put it down as it wasn't much help. I moved on to BWP which was slightly more helpful stating that spermologus has 'sometimes a trace of paler grey or silvery collar' but then gave me ' from late Spring feather fringes become sufficiently paler to create faintly scalloped pattern on back & body and by early Summer grey area of head becomes more silvery' and then 'but formation of pale, partial collar still rare.'
What about the underparts well it talks about 'plumbeous grey' now how many of you have even the faintest clue what 'plumbeous' means? I certainly didn't so more digging. Thankfully another birder obviously didn't fancy the housework either and provided the definitive answer.
So I moved on to BBi to see if it could offer any additional material, we have to go back to 1947 BB40:5, 143-144 (Wagstaff & Williamson) who when comparing specimens from Britain and Scandinavia noted 'that the collar character is not to be relied upon in separating the two races'. Reading further however it becomes apparent that the this reference is made because at least some Scandinavian individuals in their small sample did not show an obvious collar rather than some spermologus showing a collar. They draw the conclusion that 'only Scandinavian birds of the more extreme type (with reference to collars) may be recognizable in the field'
Where to go from here, well let's go Dutch. An article from Dutch Birding on the identification of Eastern Subspecies of Jackdaw that can be found here offered perhaps the best hope of sorting this one out. But no it gets even more complicated, now we have images of dark, uniformly coloured probable monedulas from an 'integration zone' that are being referred to as 'turrium'
Not complicated enough try this ' As a result of wear, spermologus may show a narrow pale line in the lower neck and some pale fringes to the mantle and underparts in early spring, both recalling monedula.' or this 'Some spermologus may show paler earcoverts and nape but never a paler collar as in monedula.' and finally ' Compared with adult spermologus, monedula has a paler nape and ear-coverts, which at most can be slightly brighter than a spermologus in breeding plumage. On most adult monedula, the underparts are slightly darker than the nape and ear-coverts but this can also be shown (albeit in darker tones) by some spermologus. The main difference with spermologus is that the underparts are plumbeous-grey and paler than in spermologus, of which the underparts are more grey-black. The dark throat of monedula contrasts much more with the underparts than in spermologus. Note, however, that some monedula only show a dark chin and a paler grey throat, sometimes of the same tinge as the underparts. In direct comparison with spermologus, the paler underparts of monedula are a very useful field mark.
Are you still with me? Subsequently I've wandered around the web and there are several reports some with pictures of monedula from the UK. Most reports seemed to be based on the pale whitish collar mark and no other field characters. After reading all this material I'm not convinced that this single field mark can be relied upon to call a monedula in the field. So was my bird monedula? Answer possibly as there were at least two separate ID features, a prominent collar line and paler grey underparts but this is probably the worst time of year due to wear to try and separate the two subspecies. Also guess what take a quick trawl around and look at when most Nordic Jackdaws are being reported, majority of UK records appear to me to be Feb-April. With less from Oct-Jan when you would perhaps expect them as a result of migration from their range. There are some pucker records with good photos showing multiple field characters and many of these come from that Oct-Jan period so maybe we just need to be a little careful about reporting Vikings.

References
Cramp, S & Perrins, C M 1994. The birds of the Western Palearctic 8. Oxford.
Wagstaffe & Williamson British Birds 40:5, 143-144
Offereins R 2003. Identification of eastern subspecies of Western Jackdaw and occurrence in the Netherlands

1 comment:

Holywell Birder said...

Thank You, I enjoyed that, think I may need to read over the points again and dig up reference material but a very interesting topic, thanks cain