1st w. GBBG vs. 1st w. LBBG (Madrid) (1 Viewer)

[la_ravachol]

Great Black-backed Gull is a rarity in my area (Madrid). I've been trying repeatedly to find a first winter that was reported a couple of days ago and today I think I found it - at least, when I left I was confident, but now I'm stuck with these nagging doubts as I am far from a gull expert and people who know much better than me have searched and not found it. Unfortunately, I didn't have a camera on me as I was just popping by again between appointments on the off chance, so no photos I'm afraid. The question I need answering is, how distinctive is the tertial 'step' on a first winter GBBG in comparison with a first winter Lesser Black-backed? I could see a clear difference between the two first winter birds I had in front of me, but perhaps I shouldn't rely on this?

In general I tend not to rely on size differences between similar species as I think this can be difficult to judge, but maybe this would have been so obvious as to have removed the possibility of subsequent doubt in my mind?

Help with this is appreciated! I don't have the chance to look again for a couple of days and I doubt it'll still be around, if indeed it was the GBBG!

 

[stevethehydra]

I have no idea about 1st-winter plumages, but the smallest GBBG is still a lot bigger than the biggest LBBG. There might just about be an overlap between exceptional individuals of marinus and argentatus/michahellis. GBBG should have a very noticeably different "jizz" as well - shorter wing projection, much bigger head and deeper bill, generally looks like a much bulkier bird - fuscus looks almost more like a Chroicocephalus sp. in comparison!

 

[fdokykcu]

Great Black-backed Gull is a rarity in my area (Madrid). I've been trying repeatedly to find a first winter that was reported a couple of days ago

Check the photos in the linked ebird list about that particular bird at Madrid-Río standing amongst several LBBG, so you can appreciate both the difference in size and plumage pattern and the tertial step
https://ebird.org/checklist/S98776877

 

[madbird]

Check the photos in the linked ebird list about that particular bird at Madrid-Río standing amongst several LBBG, so you can appreciate both the difference in size and plumage pattern and the tertial step
https://ebird.org/checklist/S98776877

Hi all, The tertial step also first attracted me to this bird (also on the river in Madrid) then it took off before I got a better look... I´ve convinced myself this is a LBBG for now