Sunday, 17 September 2017

Black-tailed Godwits

As promised a few posts back...

There are three sub species of Black-tailed Godwit Limosa limosa in the world. L. l. melanuroides, which breeds in eastern Russia, Siberia, China and Mongolia, has never been recorded in the UK so we can forget about that one, leaving us with these two...

The Icelandic Black-tailed Godwit (L. l. islandica) breeds mostly in Iceland, but also the Faeroe Islands along with a few pairs in Scotland. The majority winter in the UK, Ireland, France and Holland.

The small number of Continental or European Black-tailed Godwit (L. l. limosa) that breed in the UK (East Anglia) are at the western limit of their breeding range, with most breeding in western and central Europe to central Asia and west Russia. They winter around the Mediterranean and as far south as the west coast of North Africa, mostly Senegal.

So to summarise the above information, it would seem that islandica is an abundant winter visitor to the UK, whereas limosa is a very rare breeding bird and probably a fairly scarce passage migrant. And this is what the case seems to be on the Axe Estuary, through my observations and the on going Black-tailed Godwit colour-ringing project undertaken by the Axe Estuary Ringing Group. In fact I can't say I've ever seen/noticed a limosa here before.

Separating the two sub species is far from easy though, especially in winter plumage when on plumage they are identical.  Spring birds in breeding plumage are do-able, as are fresh autumn juveniles, and this is why I have been paying extra attention to our Black-tailed Godwit flocks this autumn as they've contained a high proportion of juvenile birds. Everything I've seen though has  looked fine for islandica, well until last Saturday morning...

A small flock (c12 birds) of juvenile islandicas have been feeding on Colyford Common at high tide over the past couple of weeks, but last Saturday morning (9th Sept) one bird really stood out and stood up! Bingo, surely my first limosa...

Juvenile/first-winter L. l. limosa on the left and juvenile  L. l. islandica on the right


The structural differences are pretty striking in the above photo. Longer necked, bigger headed, longer billed with a broader bill base and longer legged (noticeably the tibia).

Sadly the L. l. limosa at the back is out of focus in this shot


Check out the bill size difference!

L. l. limosa at the front


The above photo shows the neck difference nicely. All the islandica in the flock lacked any sort of neck bulge when they held their heads tight to their body, whereas the limosa always showed a noticeable bulge along the lower edge of the neck. Presumably this is simply down to the fact it's a larger bird with a longer neck?

L. l. limosa at the front


Looking at the actual plumage of the bird, I'm not sure how useful this is as there was so much variation in moult and wear within all the Godwits in this group. But I'm sure it's not a coincidence this was the palest and blandest bird in the flock, lacking any orange tones to the head, neck or mantle - just a buff wash. This fits well with the literature for the limosa as they are far less colourful as juveniles than the often almost bright orange islandica. Just a pity it wasn't a month earlier though when they'd all be in much fresher plumage.

It's also worth mentioning that when the flock took to the air, the size difference was just as notable in flight. It was always easy to see which one the limosa was even if you couldn't see any plumage features.

Because all I've got for sub species specific identification of this bird is structural differences, and no real plumage traits, I reckon that means I can do no more with it that write this blog post. This limosa Black-tailed Godwit would (on paper) be the first record of this sub species for Devon, and for me to submit this as a county first I would need all the boxes ticked, not just a few. Annoying yes, but when it comes to bird ID I am strict. Oh well, at least I've got a blog post out of it!

If you're after your own limosa it's very important to remember that overall size and bill length varies between sexes (and maybe age?) in Godwits like most other wading birds, so be aware that islandica will show a variety of bill lengths and body sizes. As with many things, a direct comparison makes it so much easier so it's best to study Godwit flocks, lone birds will always be tricky unless they show a particularly striking plumage.

And here's some useful links on the subject:

Birding Frontiers
http://birdingfrontiers.com/2011/07/15/more-on-continental-black-tailed-godwits/

Northumberland & Tyneside Bird Club
http://www.ntbc.org.uk/wp-content/uploads/2013/06/Black-tailed-Godwits.pdf

Handbook of the birds of the world
http://www.hbw.com/species/black-tailed-godwit-limosa-limosa

6 comments:

  1. Hi Steve, Are the findings of the AERG reliable? After all, they couldn't identify a Dusky Warbler in the hand!

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    1. Yes. They're not IDing them to subspecies in the hand (suppose they could!) but it's the resightings of their colour ringed birds, several now seen in Iceland and none recorded going east in spring.

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    2. In my Richard Chandler book he says that the scientific name for Icelandic Black-tailed Godwits is Limosa L. islandica. Has he got that wrong?

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    3. Of course not Tim, thanks for that now all edited. Should have read it properly, never been one for latin names!

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    4. I think becoming a father is distracting you from your ornithological research! At least you've got your priorities right - more than can be said for some of us...

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    5. To be honest Tim I didn't do research for this post. Just needed reminding about the third race that we will never get here to complete the post, hence the mistake as it was all from memory. I certainly don't have time for research with the two H's and birding!

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