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contd...Juvenile Caspian Gull Larus cachinnans

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Underwings

• A very distinctive feature, and at the present state of knowledge thought to be diagnostic of cachinnans, is shown in flight: the underwings are almost entirely white. There may extremely faint barring on the axillaries, some marginal coverts and tips of median and greater underwing coverts, but in most views appear virtually unmarked. The underside of the remiges, particularly the primaries, are silvery or white, appearing translucent with only the tips of the outermost primaries being darker, forming a thin dark bar along the rear edge of the outer wing.

Tail and tail coverts

• A distinctive feature, and likened to the pattern of Rough-legged Buzzard Buteo lagopus, the rump and uppertail coverts are virtually unmarked white, only small black spots or bars noted near the tips of the longest upper- and undertail coverts respectively. The tail is white basally, but shows a broad black tail band and white tip; on the upper edge thereis usually a small amount of narrow barring near the black, and there is, when fresh, also a broad white edge to the outer tail feather enclosing the black.

Bare parts

• Structurally different (as described above), but the colour of the legs are to my mind subtly different, a paler orange- or yellow-flesh, brighter than argentatus.

First-winter Caspian Gull Larus cachinnans

Summary of Important Features

Again, striking structural differences are one of the first clues to the identity of cachinnans, as is the markedly white head and body.

Identification characters aside from structure which identifies first-winter and first-summer Caspian are as follows.

Bill

• Long and slim; all dark, but sometimes with a lighter greenish or pink-grey base; no marked gonydeal point.

Head

• Clean white, often, but not always unmarked (but importantly being whiter than michahellis and argentatus - not always whiter than graellsii), with a neat half collar of dark marks forming a necklace and extending onto the mantle.

Underparts

• Virtually unmarked white, although some faint dark spotting or barring visible on upper flanks.

Mantle and scapulars

• A mixture of largely plain grey, black spots and bleached areas. Some scapulars show a pattern of a large black basal diamond joined to a very narrow dark crescent near the tip by a thin black shaft streak.

Wing coverts

• Generally faded and worn. Best character would be the greater coverts whose dark base and pale tips from dark and light bands across the wing contrasting with increasingly worn, even pale biscuit-coloured median and lesser coverts. From January onwards there may be a few new black-centred coverts (ruling out argenteus). A contrasting dark carpal mark is noted on closed wing and especially when wing opened.

Tertials

• Black, but later a worn dark brown, pattern of pale tips still visible.

Tail and tail coverts

• Prominent black tail band highlighted by white base and white, unmarked upper and undertail coverts, sometimes marked with obscure small crescents.

Underwing

• Very white with, on some, feint brown barring on axillaries and on marginal underwing coverts. The whiteness extended right across the remiges, with a dark trailing edge to the wing tip.

Herring Gull Larus argenteus (behind)