Identifying a juvenile Yellow-legged Gull
24th August 2010 Spurn, East Yorkshire
OK , here’s how the juvenile Yellow-legged Gull was identified. Health warning-there are no long-winded explanations of every feather or caveats-everywhere kind of texts – its just rough and raw. Hope you can follow it!
First picked up by Sharon (Mrs G to you!) from the caravan window. Why? Because it was harassing a Common Gull for its food item, as tenaciously as any Arctic Skua. At distance- it looked like it was going to be a skua (naked eye). Binoculars out – saw it was a juvenile type ‘large gull’ and seeing all dark outer wing assumed Lesser-Black-back. Maybe I should have thought a moment. Mediterranean Yellow-legs are littoral feeders- aggressive scavengers. The Orgreave juvenile YLG last week
flew in and immediately began harassing and chasing smaller gulls. I have a feeling LBB’s are less aggressive.
Anyway, having dismissed it, it appeared shortly afterwards flying in front of the van. Now I could see (naked eye) it has quite contrasty with white looking head and body (ground colour) land with striking black/ white tail. It landed on the beach – bins out – the first thing that started the alarm bells ringing was the greater covert bar- viewable through binoculars (couldn’t make out other upperparts details). It looked paler/‘marbled’ lacking the expected (more extensively) darker pattern/bases to these feathers of LBB. This is when I began to think it was worth a ‘proper look’ and YLG began to be a possibility.
So scope out, and SLAM! A juvenile plumaged large gull in August with lots of 2nd generation scapulars. To be precise, the first generation scapulars in these birds are brown centred feathers with variable pale creamy fringes. The second generation feathers are, roughly speaking, paler centred with dark anchor shape. LBB and Herring don’t start moulting the juvenile scapulars until September. This bird has LOTS of moulted scaps. That’s it. In my mind, it is now almost certainly a juvenile YLG- and I begin to check the other features just to ensure the identification is water tight.
So in order
1) Aggressive behaviour of large juvenile gull (Herring/ LBB type) could be useful (note to self! )
2) Dark outer wing (no window) = LBB or YLG)
3) Paler marbled grater coverts when noticed on the deck – this could be one?
4) 2nd generation scapulars in August – pretty much slam dunk
- Yes it is white headed, little dark mask and beefy bill with heavy tip – classic!
- Though very blotchy below it has white ground colour to underparts
- Loooonnnng primary extension at rest
- Double check in flight- bright white rump and tail with neat black tail band
- Inner wing looks all pale apart from secondaries. – no extra dark bar on greater coverts as in LBB
- Underwing looks dark – but is actually ‘mealie’ and less solidly dark than LBB
All these features should be visible in the photos below -laid out to reflect the identification process as it unfolded. Remember it is a lot easier in a photo still than with a dynamically moving bird!
moulting juvenile - first winter Yellow-legged Gull Spurn 24th August 2010
Following this posting, fellow Sheffield birder, Pete Wragg sent his photo of a 1st winter Yellow-legged Gull taken at Spurn last weekenddn (21st August). Pete wrote:
“Think it’s a different bird to yours, but identified basically by the same features that you mention on your blog.”
It is clearly a different individual with even more advanced moult in scapulars and perhaps (though hard to be sure) even in some coverts:
First winter Yellow-legged Gull. Spurn. 21st August 2009. Pete Wragg
OK , OK couldn’t resist one more from tonight. It is a flock of Common Terns – literally thousands of these streamed past my caravan window this evening. What a sight!
There is one other species here. Can you see it and name it and age it? Bit closer (and easier in lower shot).