Arnhem AEB413

18 October 2014, Meijendel, Wassenaar, the Netherlands

© 2018 by Vincent van der Spek

Size doesn't matter

March 8, 2018

Probable Russian Common Gull, 5 February 2012, Meijendel, Wassenaar, the Netherlands

 

I don't like using measurements as a diagnostic feature to ID sexes or subspecies. Last week was no exception.

 

After another mild winter, an unusual late cold spell hit the country early March. Temperatures dropped to minus 8 C, combined with a 7 Bft easterly. At the very end of winter... that's just killing. Litterally for the birds if they don't start moving. 

 

Rinse and I trap four Common Gulls in Meijendel, Zuid-Holland, the Netherlands on 1 March. One large bird is of particular interest since it has a wing length of 398 mm (left) and 399 mm (right).

 

Based on Malling Olsen & Larsson (2004), Demongin (2016) and Baker (2017) – that together combine many sources – everything above 395mm should be diagnostic for Russian Common Gull heinei. The tarsus (54,2 mm) is well above the average for Common Gull (50,8 mm), all other measurements fit both subspecies well.

 

But the bird just didn't look right. Or not classic anyway – as far as classic is appropriate for these subspecies. It had a speckled head, and not the desired whitish head with a speckled scarf (reminiscent of a Caspian Gull). The iris was very dark and the bill and legs were dull yellowish to greenish, instead of the prefered plain yellow.

(sorry for the crappy shots; they were made around dawn with my phone)

 

I also noticed another feature that was completely wrong for Russian: no black band on the 5th primary. 

 

Though apparently this is not a heinei, based on the much smaller wing lengths of breeding males in e.g. Great Britain (Baker, 2017), I however think it's likely that these large, wintering birds have an eastern origin.

 

Adriaens & Gibbins (2016) published an impressive Dutch Birding ID issue on the matter:

Just for the fun of it I scored the bird on the 15 features they present. On seven points the bird showed features that the majority of heinei also shows (note that quite a few of these are also majority features for canus), five features are minority features (and these fit canus much better),  and in two it was unclear. The final one - the lack of a black band on p5 - is an absolute no go.  

 

So apparently it's true: size doesn't matter!

 

We trapped an apparent canus with with a wing length more associated with heinei.   

 

The 2012 birds

In 2012 we trapped several likelier heinei candidates (also see pic on top of this post). I didn't photograph the wing well enough to asses all features in Adriaens & Gibbons (2016) properly (how was I to know what exactly to look for at the time!) but out of the 11 features that can be checked, the bird on the photograph scores 10 majority features for Russian. Only the band on the bill could have been clearer. Also note the less intense speckling on the head, the scarf, the medium pale iris and the bright yellow bill and legs.  

 

And yes, it has a solid black band on p5. The bill length was also in the range of what's considered diagnostic for heinei

How was I to know back then that I should have photographed all tongues and black wedges?​ Check the solid W-shaped black band on p5.

After a few birds in 2013 (no heinei candidates), it had been five long years since I trapped some Common Gulls. Let's hope it won't take another five!

 

References

 

Adriaens, P. & C. Gibbins. Identification of the Larus canus complex. Dutch Birding 38:1

 

Baker, J. 2017. Identification of European Non-Passerines. BTO, Thetford.

 

Demongin, L. 2016. Identification guide to birds in the hand. Beauregard-Vendon.

 

Malling Olsen, K. & H. Larsson 2004. Gulls of Europe, Asia and North America. Christopher Helm, London

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