In July we see the beginning of the UK’s annual influx of juvenile Yellow-legged Gull (YLG), as birds dispersing from breeding grounds in southern Europe arrive on our shores. I was curious to see how this would play out in Hastings given their annual presence in the Eastbourne area to the west. On the morning of the 11th I hopefully headed down to the seafront and was very happy to find a big arrival of YLG — 12 in total, mostly juveniles but a couple of other age classes too. These were seen in all the spots there are typically large gatherings of gulls on the seafront, namely Rock-a-Nore car park, The Stade beach and the boating lake.

It was a real treat to see these birds up close and study the plumage details, so I thought I’d do a bit of a deep dive in this post and share some photos and notes, particularly on the more interesting or tricky individuals. I’ve split the birds I saw into three categories: immatures, identified juveniles and unidentified juveniles.

Immatures

There were two immature birds present, the first a sub-adult which I’d hesitate to age more specifically. You can see the traces of brown in the tertials and wing coverts in the photos, as well as the green-tinged legs, but the head, bill and primaries are looking quite adult like.

The second was a striking 3CY with dark irises and a blood red orbital ring and gape. The bill is in moult while the legs are still pinkish with a hint of yellow starting to come through. The classic solid dark tertials are showing but the wing feathers are a relatively light shade of grey for YLG, as you can see in the comparison with the sub-adult below. Still noticeably darker than 3CY Herrings nearby, which is a bit clearer in the flight shots. I’ve read that eastern YLG can be a lighter grey or maybe it’s just an age thing and the next generation of feathers will be darker.

Identified Juveniles

In the end I counted 10 juveniles which I could confidently identify as YLG based on their conforming entirely or almost entirely to the established characteristics for identification at this time of year:

• wear apparent on the wing feathers;
• dropped or replaced mantle and scapular feathers;
• reddish hue to the brown of feather colouration;
• pale head with dark eye mask;
• dark brown tertials with pale tips, sometimes with limited notching;
• dark brown panel in greater coverts;
• indistinct ‘window’ in the inner primaries;
• well-defined black tail band which tapers toward the outer feathers;
• white rump with limited brown spotting.

If you’re not familiar with the feather terminology you can find a handy annotated photo on Gull Research.

Photos of all 10 individuals follow with a few notes where I thought they were interesting. I’m rarely pleased to see a dog plough into a gathering of gulls but in this instance it was quite useful as it allowed me to see and photograph almost every bird in flight.

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This individual (left bird in first photo) nicely illustrates the classic plumage hue and relative wear level of a juvenile YLG. Hard to believe but the bird behind (next one in set) is also a YLG, showing just how different individuals can look at this time of year in terms of wear and colour.

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This is the bird in the background from the previous photo set. Definitely at the darker and fresher end of the spectrum (see contrast with the juvenile in the foreground) but you can’t argue with that tail pattern and inner primary window combo!

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Bulky individual with its scapulars starting to look a bit messy with dropped feathers. Weird tail pattern on this one that I wish I’d got a better picture of.

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I didn’t get great pictures of this interesting individual unfortunately but this is probably the palest juvenile YLG I’ve ever seen, particularly on the greater coverts which look more white than brown when sitting. You can see that the feathers are quite worn and it has already replaced several 1st gen scapular feathers with 2nd gen feathers. Look at the amazing clean white tail pattern in flight!

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Really warm, almost gingery hue to the brown parts on this one.

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Here’s another which seems to have a few replaced upper scaps. Nice thin black tail band.

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Snouty bill and very long legs give this one an almost Caspy vibe.

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Quite a dark individual and relatively fresh looking compared to many of the others. Birds like this make me wonder if they could be one from the French Atlantic coast colonies, which would have made less of a journey and therefore seen less wear and sun bleaching.

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Nice marbled pattern to the scaps and coverts on this one.

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Not a typical YLG structurally with its small body and weak bill, but wear, colouration, tail and primary window look OK and it’s even dropped a scapular feather which is unlikely for LBBG at this time of year.

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Unidentified Juveniles

There were a couple of birds which presented characteristics that were intermediate between Yellow-legged Gull (YLG) and Lesser Black-backed Gull (LBBG). LBBG is a scarce breeder in East Sussex and I’m not aware of any pairs in the immediate Hastings area but, given gulls tendency to wander, it is possible that early fledging LBBG from elsewhere could show up. Digging into the research further I came across a ringing study where a first-year LBBG from Ireland had reached the Iberian peninsula by mid-July! And in fact I did see two juvenile LBBG on the 11th, both of which I only caught in flight — photos below. Both showed thick black tail bands without tapering at the edges, heavily mottled white tail base, dark inner primaries and smoky head patterns.

Despite the differences at the structural extremes, YLG and LBBG are known to show similarities in their first year. Moult progression is one reliable way to separate them, but this is not as relevant at this point in the year as many birds are still in full juvenile plumage. Descriptions of the two unidentified birds follow and then some closing thoughts on their potential identities.

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This bird was fairly small with short dusky legs, a broad black tail band and lack of inner primary window, suggesting LBBG. However the feather wear and colouration seem a better fit for YLG. Structure, bill and face mask pattern seem to be roughly intermediate between the two, although I’d lean toward YLG.

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This bird was small with an attenuated shape, weak bill and short legs, all of which which suggest LBBG. The scapulars are quite neat and the tertials have long pale edges, also pro-LBBG. However, the tail pattern, primary window and overall colouration suggest YLG. Furthermore, I noticed in one photo there’s what appears to be a 2nd gen scapular tucked away on the back with a bold YLG-like anchor pattern! Not something I’ve ever seen before but possibly just an aberrant 1st gen feather. The pale base to the bill is odd and not something I’ve seen in either species, although the 1997 Martin Garner article in British Birds says that YLG can “have a pale base to the lower mandible by the first autumn”.

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I’ll be noting both of these as Larus sp. but to be honest I suspect they are oddball YLGs. They both show many features which are pro-YLG and we know gulls can be super variable. For example, it’s not hard to find images of YLGs with thick tail patterns or very dark inner primaries. They also turned up in Hastings with a group of YLG and show an overall colouration and wear level which match up with others within that group.

This all got me thinking about whether juvenile gulls showing this kind of feather condition and colouration, at this time of year, could even be LBBGs. Could they come from further afield than the LBBGs I’m used to seeing in the UK? As the YLG has spread north, the LBBG has spread south, and there are now significant numbers of the latter breeding in SW Europe e.g. the Bay of Biscay, Iberian Peninsula and the west Mediterranean. The most recent data I could find put LBBG totals at 10935 pairs south of the English channel (compared to 46695 pairs of YLG) most of these being in the northern part of the Bay of Biscay.

These southern LBBG populations are not well studied and I couldn’t find much information on their post-breeding dispersal patterns. The well known long-distance movement pattern for graellsii LBBG is southbound migration later in the autumn. But could some first-year birds disperse north in mid-summer, perhaps alongside YLGs? I’m not totally convinced by this, mainly because research has shown (albeit 30 years ago) that where both species breed alongside each other in colonies along the French portion of the Bay of Biscay, they show little overlap in laying dates and the earliest LBBG lay about a month later than the earliest YLG.

One other thing to add is that, as we’re talking about gulls here, there’s also the hybrid possibility. We know mixed pairings of YLG and LBBG can occur and produce young (see Martin Garner’s 1997 YLG ID article in British Birds and the new Adriaens et al. gull book). I’m not sure how frequent this hybridisation is but presumably juveniles from these pairings sometimes disperse, but where to and what they might look like is a bit of mystery. Still so much more to learn about these amazing birds.