leifvester
Active member
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Belfast, Ireland - Gull ID (2 Viewers)
- Thread starter leifvester
- Start date
Valéry Schollaert
Respect animals, don't eat or wear their body or s
For me, it is too far to make a positive ID, but I think thik bill and much white is the tertials are good for Great Black-backed Gull ?
JayFeatherPL
Well-known member
I agree, the size of the bill favourables Great Black-Backed Gull. I wonder if you can ID a species of an immature gull with 100% certainty? I doubt it...They're so variable...
Valéry Schollaert
Respect animals, don't eat or wear their body or s
We can, as well as all other birds, but the concept of "certainty" itself is a philosophical question...
leifvester
Active member
Thanks for the replies guys!
What I would say is that I'd be very surprised if it was a Great Black-backed gull.
1. The beak doesn't look thick enough.
2. I would expect a GBBG to be more white around the face - this gull is quite grey in the face.
3. Not obvious from the photo, but it wasn't a huge gull. This was within binoculars range!
4. I've never seen a GBBG in that area before, so it's probably not likely, but not impossible.
What I would say is that I'd be very surprised if it was a Great Black-backed gull.
1. The beak doesn't look thick enough.
2. I would expect a GBBG to be more white around the face - this gull is quite grey in the face.
3. Not obvious from the photo, but it wasn't a huge gull. This was within binoculars range!
4. I've never seen a GBBG in that area before, so it's probably not likely, but not impossible.
lou salomon
the birdonist
Lot's of AI produced artifacts in these pics, take for instance the smooth grey appearance of head and hind neck. It's a 1cy and thus pattern of tertials and greater coverts would be crucial, none of them are well visible here.
I suspect your suggestion would be YLG, leifvester, but to ID it as such we'd need to have a better view on TT and GC. And the weird dark grey hood plus upper mantle doesn't fit anything. I don't see a GBBG either (mostly on bill shape) but any of the other large gull taxa would need slightly better pics to clinch them, you know, variability and similarities in juvenile plumage...
I suspect your suggestion would be YLG, leifvester, but to ID it as such we'd need to have a better view on TT and GC. And the weird dark grey hood plus upper mantle doesn't fit anything. I don't see a GBBG either (mostly on bill shape) but any of the other large gull taxa would need slightly better pics to clinch them, you know, variability and similarities in juvenile plumage...
leifvester
Active member
Thanks for the detailed response!
By AI produced artifacts, do you mean Artificial Intelligence? There's definitely no shinanigans, it's a pocket camera that is just low resolution unfortunately.
leifvester
Active member
I've had a stab at looking at the ratio between the length of the bill and the depth of the bill at the gonys.
From what I could find both juvenile Herring gull and Yellow-legged gull have roughly a ratio of around 2.9 - 3.1 between the length of the bill and the depth of the bill at the gonys.
Juvenile lesser black backed gulls have a ratio of about 3.3, i.e. a less pronounced gonydeal angle.
Here's the data from a sample I found for juvenile gulls. There is a fairly big range though.
HERRING:
----------------------------
Bill length: 45 - 53 (mm)
Bill depth at gonys: 15.7 - 18 (mm)
Gonys Ratio: 2.9
YLG:
-----------------------------
Bill length: 49 - 53 (mm)
Bill depth at gonys: 16.8 - 16.9 (mm)
Gonys Ratio: 2.9 - 3.1
LBBG:
-----------------------
Bill length: 45 - 49 (mm)
Bill depth at gonys: 13.7 - 15 (mm)
Gonys Ratio: 3.3
Going through the three photos made me realise just how low res they are, which also means the margin of error when measuring the bill will be high because one pixel can make a significant difference.
Across the three photos I calculated the ratios of 2.5, 2.6, and 2.7. If I reduce the depth measurements by a pixel (to account for anti-aliasing, and only use black pixels) then the ratio does become around 2.8-2.9.
Famous last words, but I think I can rule out Lesser-black backed gull based on those measured ratios.
From what I could find both juvenile Herring gull and Yellow-legged gull have roughly a ratio of around 2.9 - 3.1 between the length of the bill and the depth of the bill at the gonys.
Juvenile lesser black backed gulls have a ratio of about 3.3, i.e. a less pronounced gonydeal angle.
Here's the data from a sample I found for juvenile gulls. There is a fairly big range though.
HERRING:
----------------------------
Bill length: 45 - 53 (mm)
Bill depth at gonys: 15.7 - 18 (mm)
Gonys Ratio: 2.9
YLG:
-----------------------------
Bill length: 49 - 53 (mm)
Bill depth at gonys: 16.8 - 16.9 (mm)
Gonys Ratio: 2.9 - 3.1
LBBG:
-----------------------
Bill length: 45 - 49 (mm)
Bill depth at gonys: 13.7 - 15 (mm)
Gonys Ratio: 3.3
Going through the three photos made me realise just how low res they are, which also means the margin of error when measuring the bill will be high because one pixel can make a significant difference.
Across the three photos I calculated the ratios of 2.5, 2.6, and 2.7. If I reduce the depth measurements by a pixel (to account for anti-aliasing, and only use black pixels) then the ratio does become around 2.8-2.9.
Famous last words, but I think I can rule out Lesser-black backed gull based on those measured ratios.
Last edited:
lou salomon
the birdonist
Concerning bills in juvenile large gulls: they are still growing and thus in many cases not useful for identification. Some change their shape astonishing drastically during their first year of life. Furthermore there are a lot of atypical individuals even in adults, concerning bills. Like Caspian Gulls with pretty short bills or YLGs with pretty pointed and long bills.
Easiest to ID juv large gulls is with good flight pics from above, showing inner primaries and tail pattern. Swimming gulls are hardest to ID because many traits are not visible or mostly hidden. With better resolution photos surely your bird still would be identifiable.
Easiest to ID juv large gulls is with good flight pics from above, showing inner primaries and tail pattern. Swimming gulls are hardest to ID because many traits are not visible or mostly hidden. With better resolution photos surely your bird still would be identifiable.
leifvester
Active member
This is good to know, thank you!
I wonder from the photo is it possible at least to narrow it down to a selection?
For example, I can say quite confidently it's not a Common Gull.
What are the reasonable possibilities for this gull?
Valéry Schollaert
Respect animals, don't eat or wear their body or s
"What are the reasonable possibilities for this gull?"
Great Black-backed Gull and Herring Gull are the common large gulls there ; both have large pale area on tertials.
Great Black-backed Gull and Herring Gull are the common large gulls there ; both have large pale area on tertials.
leifvester
Active member
Probably a juvenile lesser black-backed gull
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