Jan Hein van Steenis
 ·  12 januari 2026  13:27

Nice find! I would certainly have overlooked this one...

Here it looks a bit less like a Bonaparte's than on the first photos I saw.

Julian Overweg
 ·  18 januari 2026  03:33

Interesting Alex!

Do you know any publications (describing the hybrid) that you would recommend reading?

On the 10th of november 2022 I noticed a strange looking specimen in a group of Black-headed gulls (Hardenberg, The Netherlands). Video's:
https://youtu.be/PH7tdTZ-f2s
https://youtu.be/_HxSsuaFro8
https://youtu.be/eqCbb8rzVuo

Notes from then:
- Compacter dan kokmeeuw.
- Grijze zijhalsvlek lijkt consistent aanwezig; ook bij draaien (vergelijk omringende kokmeeuwen).
- Oorvlek behoorlijk scherp begrenst (vergelijk omringende kokmeeuwen).
- Kleine zou volledig zwarte snavel hebben maar kennelijk niet altijd het geval. Zie bijv. 1e foto hier: https://www.bobsteelephoto.com/Species/bogu.html
- Snavellengte bij Kleine kokmeeuw varieert (Handboek Europese vogels deel 1).

George Sangster
 ·  18 januari 2026  12:16, gewijzigd 18 januari 2026  12:35

This case illustrates that it would be very helpful if there was a major study (eg, using photographs) in which (i) the phenotypic variation of both species is quantified, and in which (ii) the states of multiple characters are scored for the same individual gulls, so that we can see which combinations of character states occur within each species. This will surely help flagging birds with seemingly intermediate (combinations) of character states, which may represent hybrids.

Fortunately, both species are common in their respective ranges, so, while undeniably a lot of work, it should be pretty straightforward to collect data from photographs.

Given the large amounts of work involved, and the fact that there are several other (sub)species-pairs* for which such studies are warranted, it might be useful if there was a central address where people interested in participating in one or more of such studies could register their interest. This will facilitate setting up collaborations.

* eg, Pacific and Atlantic Eider; Herring and American Herring Gull; Common and Ring-billed Gull; Ringed and Semipalmated Plover; European and hudsonia Dunlin; ginginianus and percnopterus Egyptian Vulture; Grasshopper and Lanceolated Warbler; Starling and Spotless Starling.

Even if it is difficult to collect data on a reasonable number of individuals of one of the two taxa, it could still be very helpful to quantify variation in the more common taxon. For instance, a quantitative study of variation in Grasshopper Warbler would make it much easier to flag/identify a potential vagrant Lanceolated Warbler in Europe. This fits well with the old adage "to find rare birds, learn to know your common birds".

Julian Overweg
 ·  18 januari 2026  14:02

George: "it might be useful if there was a central address where people interested in participating in one or more of such studies could register their interest."

I like that idea! How about some sort of puzzle forum boards for specific taxa on the Dutchbirding site with standardised pre-set database fields for scoring specimen?

Like everybody with a Dutchbirding account could participate, making it community driven.

Peter de Knijff
 ·  18 januari 2026  14:11

A first good start would be that the data/observations underlying Dutch Birding articles are requested to be made available, e.g. as a Zenodo document, similarly to what I was requested to do with all DNA data. If e.g. that would have been done with the impressive Common gull ID paper by Adriaens and Gibbins, we would have had insight in the raw data underlying all clinching characters. Similarly, at least a list of Xeno-Canto numbers used for sound comparisons should be a minimum requirement, in addition to the various measured aspects of each individual.

Peter Adriaens
 ·  18 januari 2026  21:56

All of the data on Common Gulls (1000+ birds) is in a searchable database that is sitting on my hard drive. If anyone is interested in uploading it and making it publicly available online, I would be happy to provide it.

George Sangster
 ·  18 januari 2026  22:42

@Peter Adriaens,

An easy way to make your data set both available and easy to find is to publish it on ResearchGate as a data file associated with the full paper.

Peter Adriaens
 ·  18 januari 2026  23:50

Ik had een account maar om een of andere onbekende reden krijg ik daar geen toegang meer toe.

Peter de Knijff
 ·  19 januari 2026  07:06, gewijzigd 19 januari 2026  07:11

Ik noemde jullie artikel alleen maar als voorbeeld, Peter, omdat ik de afgelopen weken zelf weer in de Stormmeeuwen ben gedoken (met vorst en sneeuw zit het strand hier vol Stormmeeuwen), maar goed om te weten dat de hele dataset evt. beschikbaar is.

Ik vind Zenodo wat gebruiksvriendelijker dan Research maar dat is een kwestie van smaak.