Steve Hale asked me to do a short piece on the separation of these three species in juvenile plumage, which is the first plumage that a young gull has prior to the start of a body moult into first-winter plumage, which commences from late summer onwards.
|juv Herring Gull|
The place to start is with the familiar Herring Gull, the archetypal ‘seagull’ of seaside resorts, but also occurring commonly inland. As the photograph shows, juvenile Herring Gulls are very brown, with a black bill and pink legs. Their fresh juvenile plumage is immaculate, heavily mottled with brown on the head and underparts and also with strong chequering right across the upperparts. Note in particular that (a) all the wing coverts are chequered, including the greater coverts, which is the lowest band of feathers along the bottom of the closed wing, just above the flanks and (b) the tertials also have rather chequered white fringes (the tertials are the group of feathers that cloak the base of the primaries at rest).
In flight, juvenile Herring Gulls are very brown, with the rump and uppertail-coverts, and also the base of the tail, being heavily patterned with brown barring and blotching. In addition, when seen from below in flight, juvenile Herring Gulls have rather translucent inner primaries, forming a large, rather square pale area that the light shines through. This is usually referred to as a pale ‘window’.
|juv Lesser Black Backed Gull|
Lesser Black-backed Gull
Lesser Black-back is now a very common breeding bird in Bristol and Bath. It is similar in size to Herring Gull but it is structurally different. At rest it has a weaker bill and shorter legs, but most distinctive is that it is a slimmer, more attenuated bird, with long primaries that project well beyond the tail to form a long, tapered rear end. This difference is linked to the fact that, whereas Herring Gull is a relatively sedentary species, Lesser Black-back is a strong migrant, much of the population heading off to winter in Portugal, Spain and West Africa, although large numbers also remain behind in Britain.
These structural features are shown well in the photo. Note also that, compared with juvenile Herring, juvenile Lesser has dark, rather sooty plumage with a darker area around the eye. Note in particular that the blackish teritals have white fringes to the individual feathers rather than the pale notches shown by juvenile Herring. Another difference is that the band of greater coverts (along the bottom of the closed wing, immediately above the flanks) is more solidly dark, lacking juvenile Herring’s obvious notching.
|juv Yellow-legged Gull|
Yellow-legged Gulls breed in the Mediterranean but, in recent years, the species has spread northwards and is now breeding in western France and Switzerland; the odd pair has even bred in Britain, most frequently in Poole Harbour. Locally, the species is most likely to be seen at Chew Valley Lake, where adult birds have the distinctive habit of patrolling the lake at a height of about 30 feet, rather like a Gannet searching for fish. This behaviour is so distinctive that you often identify them at considerable range, even with the naked eye! They also have a strong habit of sitting on buoys, rather like Great Black-backed Gulls. Juveniles start to turn up in July and often join the resident gulls begging for food on the dam walls at Herriott’s Pool and Heron’s Green Bay.
Strucurally, they are most similar to Herring Gull, being rather large and bulky, but they average even larger and more sturdy than Herring, with a stronger, heavier bill and longer legs. Their plumage is essentially mouse brown but with contrasting buffy-white fringes to all the upperpart feathers, with limited mottling. Like juvenile Lesser Black-back, the tertials are plain brown with white fringes. The greater coverts too are plain brown, forming a dark band along the lower border of the closed wing, rather like that shown by juvenile Lesser Black-back. However, what is most distinctive about juvenile Yellow-legged is that it has a very white head, lightly streaked with pale brown, but with an ill-defined but nevertheless quite distinctive dark mask behind and below the eye. The underparts too are also very white (mottled with brown), as are the rump and tail, the white contrasting strongly with the thick black tail band. Thus the rump and tail are much more black-and-white than the browner tail of a Herring Gull. In flight, Yellow-legged Gulls also show a transluscent ‘window’ on the inner primaries, although this is not as obvious as on Herring Gull.
|another juv Yellow-legged Gull|
Separating these three species in immature plumages may seem daunting, but simply compare the birds shown in the accompanying photos. Forget the details – just look at them. They really are different and, with practice, their separation becomes second nature!