Larus cachinnans

(last update: February 16, 2013)

Coordinator:
Peter Adriaens (Belgium)
Ies Meulmeester (Netherlands)

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cachinnans plumages

From the Rarities Committee's files - Identification of Caspian Gull. Part 2: phenotypic variability and the field characteristics of hybrids, by Chris Gibbins, Grzegorz Neubauer and Brian Small, IN: BB 104/2011.

Table 2. Traits and scores used to characterise birds in first-winter plumage (October-March inclusive).

 

Trait Score Description
Extent of scapular moult 0 no first-generation feathers remaining
1 a small number (<1/3) of first-generation feathers remaining
2 a significant number (>1/3) of first-generation feathers remaining
Greater-covert pattern 0 simple pattern with brown centres and sharp white edges, with no white vermiculation or notching
1 white edges with delicate notches or vermiculation; or dark brown centre with white tip to 1/3 of length (i.e. white restricted to tip or distal third)
2 clear white notches / barring creating a delicate 'piano key' pattern along the whole edge / feather; but much of feather dark
3 lots of white (more than 1/2 of coverts looking white) distributed along the whole feather, or a bold notching ('piano key' pattern)
Bill shape 0 Very long and slim, no visible gonydeal angle (L:D ratio >2.8)
1 Slim, slight gonydeal angle (ratio 2.4-2.79)
2 Intermediate (ratio 2.0-2.39)
3 Short and deep, well marked gonys angle (ratio <2)
Leg length 0 Long and slim looking
1 Moderately long
2 Short or short and stocky
Ventral bulge 0 present
1 absent
Primary projection 0 very long (ratio >0.6)
1 moderately long (ratio 0.5-0.59)
2 medium (ratio 0.4-0.49)
3 short (ratio <0.4)
Moult: greater coverts 0 all or almost all new (>75%)
1 51-75% new
2 34-50% new
3 10-33% new
4 one or two feathers moulted
5 no moult
Moult: median coverts 0 all or almost all new (>75%)
1 51-75% new
2 34-50% new
3 10-33% new
4 one or two feathers moulted
5 no moult
Moult: tertials 0 3 or more new
1 2 new
2 1 new
3 all old
Darkness of head and body 0 totally white
1 reduced grey wash or streaking (confined to flanks and/or single streaks around nape)
2 light streaking/wash to head (incl. some dark around eye); isolated streaks/blotches on body. Overall, body looks more white than brown
3 well streaked: dark mask around eye and/or streaking covering the whole head/face; body with extensive but moderately dense streaks/mottles
4 strong and dense streaking/mottling on body and head making it appear almost wholly dark
First-generation tertial pattern 0 diffuse white tip (like Common Gull Larus canus)
1 fine pale fringe around distal portion (like classic michahellis), possibly also with some vermiculations
2 edges moderately notched
3 edges strongly notched and/or some dark barring or pale patches across the feather on some or all tertials
Second-generation scapular pattern 0 uniformly silvery-grey, darker patterning absent or very faint
1 silvery-grey background, pattern stronger than on 0, but lacks strong barring or central dark diamonds (only dark shafts and subtle anchors), with only a minority (one or two) of such feathers admixed
2 strong, contrasting shaft-streaks, anchors and/or dark central diamonds, but these more patterned feathers are less than 1/2 of all; ground colour creamy or silvery-grey, possibly with some grey feathers mixed in
3 strong pattern described in 2 on most (more than 1/2) of feathers, but possibly also one or two plain grey feathers or feathers with grey ground tone
4 all feathers contrastingly patterned (with dark cross bars or diamonds), lacking plain grey feathers; feather centres buffy-brown