11/03/2011
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Juvenile Yellow-legged Gull

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Juvenile Yellow-legged Gull (Galicia, Spain, 18 August 2010). Photo by Lmbuga (commons.wikimedia.org).
Juvenile Yellow-legged Gull (Galicia, Spain, 18 August 2010). Photo by Lmbuga (commons.wikimedia.org).

The problem

The identification of immature large gulls is not everybody’s cup of tea, but our understanding of this difficult group has improved tremendously over the past 10 years and many forms that were once virtually unknown in Britain are now routinely identified. The commonest of this new wave is Yellow-legged Gull, a predominantly Mediterranean species that has spread up the west coast of France and now even breeds, albeit in very small numbers, in southern England.

Towards the end of the summer, there is a major northward influx into southern Britain, with peak numbers occurring from July to September. At this time, considerable concentrations can be found in some coastal areas and the species also penetrates inland to large lakes and reservoirs. Given a reasonable view, the adults are easily identified, but how do you pick out and identify juveniles?

First-winter Yellow-legged Gull (Sandown, Isle of Wight, October 2004). Note the heavy, blunt-ended bill, thevery white-looking head and the plain, white-fringed tertials with no pale notching. Photo by Kris Gillam.
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The solutions

General appearance

Yellow-legged tends to be somewhat larger and more powerful-looking than Herring Gull, with a longer, heavier and more bulbous bill that has a deep and rather blunt tip. It also tends to be deeper-chested and rather long-legged, sometimes producing a gangly impression. At rest, juveniles are mid-chocolate-brown, with upperpart feathers showing contrasting white fringes that produce a strongly scalloped appearance reminiscent of juvenile Great Black-backed Gull.

Young juveniles tend to look dusky as a consequence of fine streaking across the crown, nape and cheeks, but the head, neck and upper breast become quite white as the birds mature. Both before and after it whitens, the head shows a large greyish smudge that extends back through the eye to form an ill-defined mask. A useful aidemémoire is that the combination of white head, dark eye smudge and white-fringed upperpart feathering can, with a bit of imagination, suggest a giant juvenile Mediterranean Gull.

The lower nape is finely but noticeably streaked, forming a band above the upper mantle and extending around the sides of the neck. Many individuals show dark bases to the greater coverts that form a band across the lower edge of the wing and, when visible, this may be emphasised by the dark secondaries. Unlike in juvenile Herring Gull, the tertials are plain brown with white fringes; when present, white indentations are confined to the tips, many showing a dark anchor-shaped mark at the tip of the tertials, white indentations behind, then a more solidly dark basal area. The underparts are variably streaked and blotched with brown, down to the belly and flanks. A line of heavy black diamond-shaped mottling down the sides of the undertail coverts is noticeable.

In flight

If you have a candidate, wait until it flies. Yellow-legged shows a rather narrow but clear-cut jet-black tail band that contrasts with the pure white base of the tail, uppertail coverts and rump, all of which show only small amounts of black mottling.

Juvenile Yellow-legged Gull (Portland Bill, Dorset, July 2006). The most obvious feature in flight is the narrow, clear-cut black tail band that contrastswith the white tail base and rump. Note also the contrasting black secondaries. Photo by Martin Cade.
Juvenile Yellow-legged Gull (Lake, Isle of Wight, July 2004). From below, Yellow-legged has a less obvious pale ‘window’ on the inner primaries than Herring Gull, and most show contrasting dark brown underwing coverts. Photo by Kris Gillam.
Juvenile Lesser Black-backed Gull (Walney Island, Cumbria, July 2007). This bird was photographed in strongsunshine but juvenile Lesser normally looks darker and sootier in flight. When closed, the tail looks almost wholly black. Photo by Steve Young (www.birdsonfilm.com).
Juvenile/first-winter Herring Gull
(Seaforth, Lancashire, November 2006). Juvenile Herring looks duskier-headed than Yellow-legged, and note the moreuniformly plain underwings, with a noticeable pale inner primary ‘window’. Photo by Steve Young (www.birdsonfilm.com).

The very dark secondary bar contrasts quite strongly with the rest of the wing and on many individuals there is a second dark bar across the outer greater coverts, in front of the secondary bar. Although it shows a pale ‘window’ on the inner primaries, this is much less obvious than that shown by Herring Gull. The underwing coverts are somewhat variable, but they often stand out as dark chocolate-brown, contrasting with the remainder of the underwing, which appears predominantly greyish.

In flight, Yellow-legged’s wings are noticeably longer and more pointed than those of Herring Gull and are often distinctly arched when it glides, making it strongly reminiscent of a skua. When approaching front-on, it shows prominent buff ‘landing lights’ at the bend of each wing, which are much more obvious than the equivalent marks of juvenile Herring and Lesser Black-backed Gulls.

Behaviour

On reservoirs, Yellow-legged Gulls often patrol quite high above the surface and sometimes plunge for fish from low elevations in an almost Gannet-like manner. More usually, they scavenge dead fish and can often be seen hanging around behind a feeding Great Black-backed, taking second place in the pecking order ahead of Herring and Lesser Black-backed Gulls.

Juvenile Yellow-legged Gull (Portland Bill, Dorset, July 2006). Young juveniles are usually pale headed, with adiffuse grey mask through the eye. Note also thecontrastingly pale-fringed upperparts and the heavybarring on the undertail coverts. Yellow-legged Gullsoften look deep breasted and long legged, and canappear ‘robust’. Photo by Martin Cade.

Since some male Yellow-leggeds are very large and heavy-billed, some juveniles can be mistaken for Great Black-backeds, which are superficially similar in plumage. This is particularly true in flight. If in doubt, Great Black-backed has an obviously narrow tail band that has rows of thin black bars in front of it, creating an ill-defined and rather messy pattern.

Great Black-backed should, of course, always look considerably larger and more powerful, with an extremely large and heavy-ended bill.

Herring Gull

Juvenile Herring Gull is distinctly paler brown in colour than juvenile Yellow-legged, with wing coverts that appear more chequered. Its head lacks an obvious eye mask and is browner, therefore not contrasting with the body. It also has a less powerful bill.

In flight it shows a thicker dark brown tail band that does not contrast with the base of the tail, uppertail coverts and rump; these show heavy and rather messy brown barring. Compared with Yellow-legged, Herring has proportionately shorter and less pointed wings. The underwings of juvenile Herring are usually more uniformly brown, lacking Yellow-legged’s marked contrast between the dark brown underwing coverts and the greyish flight feathers. Two other features shown by Herring Gull are distinctly notched fringes to the tertials, the centres of which are a paler shade of brown, and a more obvious pale window in the inner primaries that is visible from above and below.

Lesser Black-backed Gull

Lesser Black-backed is distinctly smaller and less heavily built than most Yellow-legged Gulls and, being a longer-range migrant, it has rather long, narrow and pointed wings. At rest, it looks ‘long and low’, with long, pointed primaries and a relatively small bill and shortish legs (compared with Yellow-legged).

Juveniles are dark and smoky-looking, with dark back, scapulars and wing coverts, the individual feathers being less fringed and notched with dark buff. The dark tertials are relatively plain with a narrow white fringe, lacking both the barred tips of many Yellow-leggeds and the more obvious notching of Herring Gull.

Juvenile Lesser Black-backed Gull (Bristol, July 2007).Juvenile Lesser Black-back is darker and generally sootier looking than juvenile Yellow-legged, with a dusky head and less contrasting dark buff mottling on the upperparts. Note that the tertials are plain with a narrow pale fringe. Lesser looks long-winged, but this young bird has not yet fully grown its primaries. Photo by Keith Vinicombe.

In flight, the wing coverts contrast much less strongly with the primaries and secondaries. Unlike in Herring and Yellow-legged Gulls, in juvenile Lesser Black-backed the black of the secondaries extends right across the inner primaries, forming a solidly dark rear edge to the wing and lacking the obvious pale windows shown by Herring and, to a lesser extent, Yellow-legged. The underwing too is dark, with chocolate-brown underwing coverts like those of Yellow-legged Gull, but these show relatively little contrast with the dark grey flight feathers.

Lesser Black-backed has much more black on the tail, covering all but the base, and in flight the tail usually appears all black, contrasting with the white rump and uppertail coverts.

Post-juvenile moult

As it breeds further south, Yellow-legged Gull nests earlier than both Herring and Lesser Black-backed and, as a consequence, the young mature earlier.

By late summer, many juvenile Yellow-leggeds will already look more worn than equivalent-aged Herring and Lesser Black-backed Gulls and, by August, many will have started to moult into first-winter plumage. Their back and scapulars then acquire paler gingery-cream and even greyish feathers, with a dark shaft streak and a prominent double dark anchor mark. Herring Gulls and Lesser Black-backeds normally do not begin to acquire this first-winter patterning until at least September.

By late winter, many Yellow-leggeds start to show plain mid-grey feathering in their mantle and scapulars and, being darker than the grey of Herring Gull, these feathers make it easier to recognise Yellow-leggeds with confidence.

Individual variation

For the sake of simplicity, I have described only classic individuals in this article. It must be remembered that all birds vary individually and this can be particularly marked in young gulls. Once they start to moult, their identification is made more complicated by the fact that individuals vary in the rate at which they acquire their subsequent plumages.

Another problem is that, in western areas at least, some Yellow-legged Gulls are more like Lesser Black-backeds in size and shape, and it may well be that these are smaller, shorter-legged, stubbier-billed Portuguese birds that have headed north with migrating Lesser Black-backeds. It is easy to get bogged down with all these complications but, with perseverance, classic individuals should be readily identifiable. We have to accept, however, that we will sometimes come across confusing individuals that are best left unidentified.

For more detailed information on the subject, an essential reference is the excellent paper by Garner and Quinn (1997).

Acknowledgement

I am very grateful to Kris Gillam and Martin Cade for allowing me to use their excellent and instructive photographs.

Reference

Garner, M, and Quinn, D. 1997. Identification of Yellow-legged Gulls in Britain. British Birds 90: 25-62.