Monday 30 July 2018

Tricky Yellow-legged and a nice easy Juv

The long-winged, high-chested, long-legged and small, round-headed appearance sent me down the 'Caspian' path. The positioning of the small dark eye looked promising too. Although the bill is undeniably thick-based I felt it tapers to more to the shape of Caspian as opposed to the oft-quoted 'hatchet' bill of a Yellow-legged Gull (created by steep gonydeal angle).
I thought I was on to a Caspian Gull this morning. The bird was resting on Exmouth cricket pitch and was easily picked out by its darker grey upperparts. It's a second-summer bird and I felt that structurally it was a better fit for Caspian. With a bird of this age, and in this state of moult, there are no real diagnostic features to go on, but it should ideally show a small white mirror on p10 and this bird most certainly doesn't. That feature can however be absent on Caspians, but arguably would make this more likely a hybrid and therefore less safely identifiable as Caspian. Mike Langman has seen the photos and agrees it looks structurally ok for Caspian, but he was concerned about the thickness of the bill, and of course the lack of white mirror on p10. Tim Worfolk managed to see the bird before it flew, and cautiously felt it looked ok for Caspian (though a little thick-billed), but wanted to look more closely at the upperwing pattern before committing to an id. And finally, thanks to Tim, Martin Elliot has seen photos of the bird and thinks it's just Yellow-legged Gull. Gulls are rarely straightforward but rest assured I won't be submitting this as a Caspian!
Otherwise a couple Mediterranean Gulls and another juvenile Yellow-legged Gull were present earlier on.

It's so tricky judging size and structure of gulls. To my eye this looks to have long tibia and a small rounded head. It lacks the brow and fierce look that I normally associate with Yellow-legged Gulls, and I'd expect the eye to look paler. Gulls however are so variable, that none of these features hold much weight, and may be interpreted completely differently by other observers.

Lack of a mirror on p10 raises concerns about the identification. Otherwise the black band on what is apparently p5 is ok for both Caspian and Yellow-legged, so isn't really of any help.

50% of the small gulls on the cricket pitch were Meds.

Second summer Mediterranean Gull.

Juvenile Yellow-legged Gull (with a juvenile Herring Gull to its right).


  1. Good honest write up Matt. Easy with hindsight (and after the Martin Elliott verdict) but I think I can see why the head shape maybe does better fit YL - a little too rounded on the forehead (more convex than concave) and the legs a bit too robust for a Caspian. 2nd summer/3cy just about the worst age to ID these spp.; no reliable plumage differences (apart from P10 mirror if present) so all we've really got to go on is structure. Haven't seen nearly enough Caspians so always good to get the opinion of a real expert!
    Glad to see it anyway so thanks for the call.

  2. Hi Tim - oops p10, I've been banging on about p9 for some reason?! I've changed it now. Agree with head shape comments. Seen your twitter feed and head shape looks really different in your shots. Far more YLG-like. Really appreciate your comments as always. All the best. Matt

  3. Good write up mate and it goes to show just how (insert swear word) difficult they can be. Thanks for the text and shame I was in work. I’m home working tomorrow so I may go and have a look out of curiosity and see the bird for myself. Unless it’s dkne a bunk of course. I’d love to see it simply for the learning curve.

  4. Thanks Spencer. YLGs invariably do 'do a bunk'! Cheers. Matt

  5. Good Write up Matt, it is a tricky age to nail plumage features and we know Caspians do vary in structure but then throw in the chances of Y-l Casp hybrids and multi generational mixes it's not straightforward even when you have a really long necked, legged and billed bird - this one did look very hefty bill wise, despite showing that high chest, dark eye and very long tibia and legs (albeit thick, as pointed out be Martin) we thought looked better for Caspian. Those shots of Tim's in flight give it quite a short thick neck look as it was taking off - I suspect a Caspian would have looked very long necked on take off.

  6. Thanks Mike - yep, I couldn't believe how different the bird looked in Tim's photos. I wouldn't have even considered Caspian on those shots. All the best. Matt