01/01/2010
Share 

Glaucous and Iceland Gulls

113f2167-142d-46dc-8cfb-fe53100bbfd4
Glaucous Gull by Steve Young
Glaucous Gull by Steve Young

Key featured species

  • Iceland Gull Larus glaucoides
  • Glaucous Gull Larus hyperboreus
  • Kumlien’s Gull Larus glaucoides kumlieni
Content continues after advertisements

The problem

These two Arctic gulls are, to all intents and purposes, identical in plumage and must be separated by structural features.

The solutions

Size and structure

Glaucous is a large gull, often approaching Great Black-backed Gull in size. It appears powerful and heavy-bodied, and often shows a pronounced ‘tertial step’ at rest. In flight it looks broad-winged and barrel-chested, with a slow, lumbering flight. Iceland is distinctly smaller, being roughly the size of a Lesser Black-back. Structurally, it is helpful to think of Glaucous as resembling a big Herring Gull, whereas Iceland is more similar to Lesser Black-backed Gull or even a very large Common Gull, with its rounded head, sleek features and long primaries. However, Iceland has a rather stocky body and can look rather short-tailed in flight, as well as having proportionately shorter legs than Glaucous.

Primaries

With a bird at rest, concentrate on the primaries. Glaucous has relatively short, blunt primaries that are proportionately similar in length to those of Herring Gull. Iceland Gull has long, tapered primaries that project well beyond the tail, producing an attenuated look to the rear end.

Head shape

Glaucous has a rather sloping forehead and a flat crown with a distinct angle at the juncture of the crown and nape. Iceland has a much more rounded head. It is thus a gentler-looking, less fearsome bird than Glaucous Gull, but note that head shapes can alter with attitude.

Bill shape

Glaucous has a long, thick but rather parallel-edged bill, although note that, unlike Great Black-back, its gonydeal angle is shallow. Iceland’s bill is distinctly shorter, slimmer and stubbier-looking.

Bill colour

In its first winter, Glaucous has a bright pink bill with a clear-cut and contrasting ‘dipped in ink’ black tip. Iceland has a predominantly black bill with variable amounts of pale coloration gradually appearing at the base. By the end of the winter, this may be relatively extensive, although rather than being pink, it tends to be a dull greeny-grey, yellowish or ivory colour. In addition, the distal third of the bill remains black, with this extending back slightly along the cutting edge and blurring into the paler base. In its second winter the bill of Iceland may be much more similar to that of Glaucous, with a pink base and a relatively clear-cut black tip. Note, however, that in both species the extreme tip is actually pale. If in doubt about the ageing, note that most second-winters have pale eyes (dark on first-winters). By their third winter, the bills of both species become more adult-like and there are no significant differences between them.

First-winter plumage

In their first winter, both species look pale and variably ‘biscuit-coloured’, and it is their white primaries that allow instant separation from Herring Gull. Unlike Herring, they moult few feathers until well into the winter and this explains why most first-winter Glaucous and Iceland Gulls look so pristine and immaculate: they are in fact still largely in juvenile plumage.

First-summer plumage

By their first summer, both species start to look bleached and worn and, therefore, rather scruffy.

Second-winter plumage

A complete moult in the summer ensures that second-winters regain their smart appearance.They tend to look paler and creamier than in their juvenile/firstwinter plumage although, again, they are variable. Distant birds, particularly those in flight, are difficult to age and should be logged as ‘first- or second-winter’.

Third-winter plumage

Both species may start to acquire grey feathering in their mantle and scapulars by their second summer and, by their third winter, this should be extensive across the back and scapulars, whereas the wings remain largely whitish. Adult plumage is acquired in the fourth winter.

Kumlien’s Gull

A small minority of Iceland Gulls in Britain are of the form kumlieni, or Kumlien’s Gull, which breeds on Baffin Island and elsewhere in north-eastern Canada. Adult Kumlien’s are easily identified by the presence of varying amounts of grey in the wing-tip. Immatures are very difficult to separate in their first winter but become progressively easier with age, the presence of varying amounts of darker brown in the primaries being the essential difference from Iceland.

Glaucous x Herring Gull hybrids

Glaucous and Herring Gulls frequently interbreed, especially in Iceland, so beware of hybrids. Check any apparent Glaucous Gull for hybridisation; any traces of black in an adult’s primaries or dark brown in the primaries and tail of an immature would probably indicate that the bird is not pure.

Albinos

Although second-year Glaucous and Iceland Gulls are whiter than first-years, particularly when worn, if you come across a large gull that is pure white, then it will almost certainly prove to be an albino Herring or Lesser Black-back (or, strictly speaking, a near-albino if it lacks a pink eye). A careful evaluation of its structure should be the starting point. Despite the pitfalls and caveats, classic Glaucous and Iceland Gulls are not difficult to locate or identify, and they certainly liven up a dull winter’s day.

Glossary

  • Gonydeal angle: the angle of the downward-pointed triangular projection (gonys) near the tip of a large gull’s lower mandible.
  • Tertial step: the drop down in level from the upper edge of the uppermost tertial to the upper edge of the primaries, when the gull is viewed side-on at rest.