Friday, 20 January 2017

Was it a Caspian afterall?

Well this is a tad embarrassing and unsatisfactory and also a good example of why I usually let others do the gull finding. Wasn’t it nice when we just had Herring Gulls? I’ve just had a nostalgic look at Peter Grants Gull book - the authorative text in the 1980’s - and cachinnans was just a subspecies which warranted 9 lines of text whereas now it warrants pages and pages and huge ID articles).

The gull which I featured in yesterdays post after the Glaucous Gulls was clearly strange enough to get my attention and document it and although it was Caspian Gull that was going through my mind the bird didn't match my own mental picture of what a 1st winter Caspian should look like – an image formed by pictures of “classic” birds on the web plus this well watched 1st winter from 2 winters ago (Caspian Gulls are still rare bird in Norway with few oppurtunities to study them around Oslo). When I got home I therefore was more interested in deciding whether the second Glaucous was a hybrid or not and didn’t spend too much time on the Caspo like creature. When I eventually did look at it my interest was again aroused although I was thinking more along the lines of a hybrid and I sent some pictures to Sindre M who agreed that it could be (probably was) a hybrid and I may have left it that but felt it was interesting enough to put it out on the Facebook group Western Palearctic Gulls asking whether there were others who thought it contained Capsian genes. The answers didn’t take long to arrive (despite the late hour) and there were immediate comments that it was a pure Caspian. This was a surprise as I had half expected comments along the lines of strange Herring Gull but the general consensus (with the excpetion of half of the Norwegian and Finnish commentators who prefer hybrid) was that it was a Caspian and Lou Bertalan even went to the trouble of scoring it on the Gibbons et al scoring system from a British Birds Article and placed it right on the Caspian side of the Caspian/hybrid threshold. Now I will be honest and not claim to fully understand how he has scored the bird (requires more experience of this field than I can claim to have) but based on this feedback then it would seem that the bird may be good! In an out of range context it might not be the classic looking bird we would want to find in Norway but equally it isn’t a Herring either and all these LWHG have enormous variation in plumage and structure such that where the lines are drawn are sometimes quite arbitrary and DNA apparently doesn’t always help either…..

I have posted the pictures on the Norwegian reporting system asking for comments but do not expect to receive any. The Norwegian birding community which is always shy/apathetic/worried about reputation (delete based on personal opinion) is currently going through a cyclical low in engagement  and I think at the moment you could post a picture of a Peacock labelled as a Blue Tit and nobody (OK there are a couple of people who care) would be arsed to comment.

So we will see where this gull ends up. At the end of the day it will be my fellow NSKF members who will be responsible for making judgement on the bird (unless the species gets removed as a national rarity before then.…)

Here are my pictures of the bird (yesterday’s plus a couple more) plus the scoring done by Lou Bertalan on FB based on the first 2 pictures.

And Lou Bertalan's scoring (from Facebook):

Extent of scapular moult
1 a small number (less than 1/3) of first-generation feathers remaining

Greater-covert pattern
1 white edges with delicate notches or vermiculation; or dark brown centre with white tip to 1/3 of length (i.e. white restricted to tip or distal third)

Bill shape
1 Slim, slight gonydeal angle (ratio 2.87, so actually >2,8 but there is a slight gonys angle visible)

Leg length
1 Moderately long

Ventral bulge
0,5 - there is a very slight bulge visible but note especially the flat belly in front of it!

Primary projection
1 moderately long (ratio 0.5

Moult: greater coverts
5 no moult

Moult: median coverts
4 one or two feathers moulted

Moult: tertials
3 all old

Darkness of head and body
1 reduced grey wash or streaking (confined to flanks and/or single streaks around nape)

First-generation tertial pattern
1 fine pale fringe around distal portion (like classic michahellis), possibly also with some vermiculations

Second-generation scapular pattern
2 strong, contrasting shaft-streaks, anchors and/or dark central diamonds, but these more patterned feathers are less than 1/2 of all; ground colour creamy or silvery-grey, possibly with some grey feathers mixed in.

so this makes a score of 21,5 which is still within cachinnans, close to the border to hybrids. but it also illustrates some weakness of this scoring system. covert moult weighs too much, imo (5 points for no replaced GC!), there is no criteria for rectrices pattern which personally i give a lot of weight, and it simplifies matters of 2nd gen. scpaular pattern: there are certain types of scapular patterns and each one should be scritinized separately.

what i'd still discuss in this bird is: head jizz (mentioned as not good for caspian gulls) - yes, could sit on a weak female YLG too, especially with the slight eye smudge, but caspians can show even more dark striation around eye than this. scapular pattern is of the shaggy type with one central transversal mark and only a weak thin (or absent) subterminal band. this is a common type in caspian, can appear in other taxons too but usually more bold (double anchor in YLG, bold subterminal bar giving a scaly look in HG), which i think is often underestimated because one likes to have the nice diamond shapes or just shaft streaks as typical cachinnans pattern - but this distorts reality since at least half of all 1st winter caspians don't show this kind of expected pattern but the one more similar with the other taxons. tail in this bird is very good for cachinnans, inner wings shows the nice venetian blind with p2-4 showing pale lozenges etc...

With regards the score of 21.5 (which is a bit cheeky as I don't think the system was meant to allow half points) the range for Caspian is 12-25 and the range for hybrid 22-32 so as you see right on the (edge of) the border.

Today I went birding at Fornebu. I didn’t find any pipits (had been talk of something possibly rare there yesterday) but the reedbed at Koksa was positively hopping with birds. A flock of Long-tailed Tits were feeding in the reeds along with good numbers of Blue Tits, Great Tits, Wrens, a Robin and surprisingly 5 Goldcrests. Best of all though was hearing at least a couple of Bearded Tits which wouldn’t show themselves but at least dispels my previous conclusion that they had moved on/perished.
A Long-tail where there should have been a Beard

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