Larus cachinnans

(last update: February 16, 2013)

Coordinator:
Greg Neubauer
Marcin Przymencki
Albert de Jong
Mars Muusse

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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. Percentages of sample first-winter birds with trait scores for selected plumage, structural and moult characteristics.

 

Trait Score Description Herring
(n-85)
Caspian
(n=63)
Hybrid
(n=12)
Extent of scapular moult 0 no first-generation feathers remaining 13 92 78
1 a small number (<1/3) of first-generation feathers remaining 43 8 22
2 a significant number (>1/3) of first-generation feathers remaining 44 0 0
Greater-covert pattern 0 simple pattern with brown centres and sharp white edges, with no white vermiculation or notching 0 3 0
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) 0 63 12
2 clear white notches / barring creating a delicate 'piano key' pattern along the whole edge / feather; but much of feather dark 6 30 38
3 lots of white (more than 1/2 of coverts looking white) distributed along the whole feather, or a bold notching ('piano key' pattern) 94 4 50
Bill shape 0 very long and slim, with little/no visible gonydeal angle (L:D ratio >2.8)  0 11 0
1 slim, slight gonydeal angle (ratio 2.4-2.79)  3 67 37
2 intermediate (ratio 2.0-2.39)  91 20 63
3 short and deep, well-marked gonydeal angle (ratio <2.0)  6 2 0
Leg length 0 long 0 14 12
1 moderately long  13 46 50
2 short 87 40 38
Ventral bulge 0 present 14 62 34
1 absent 86 38 66
Primary projection 0 very long (ratio >0.6) 6 72 56
1 moderately long (ratio 0.5-0.59) 38 25 33
2 medium (ratio 0.4-0.49) 45 3 11
3 short (ratio <0.4) 11 0 0
Moult: greater coverts 0 all or almost all new (>75%) 0 0 11
1 51-75% new 0 3 0
2 34-50% new 0 2 0
3 10-33% new 0 24 0
4 one or two feathers moulted 0 36 11
5 no moult 100 35 78
Moult: median coverts 0 all or almost all new (>75%) 0 0 0
1 51-75% new 0 13 0
2 34-50% new 0 20 11
3 10-33% new 0 35 0
4 one or two feathers moulted 1 13 22
5 no moult 99 19 67
Moult: tertials 0 3 or more new 0 10 11
1 2 new 0 8 0
2 1 new 0 16 0
3 all old 100 66 89
Darkness of head and body 0 totally white 0 0 0
1 reduced grey wash or streaking (confined to flanks and/or single streaks around nape) 0 41 0
2 light streaking/wash to head (incl. some dark around eye); isolated streaks/blotches on body. Overall, body looks more white than brown 17 43 22
3 well streaked: dark mask around eye and/or streaking covering the whole head/face; body with extensive but moderately dense streaks/mottles 68 16 78
4 strong and dense streaking/mottling on body and head making it appear almost wholly dark 15 0 0
First-generation tertial pattern 0 diffuse white tip (like Common Gull Larus canus) 1 65 33
1 fine pale fringe around distal portion (like classic michahellis), possibly also with some vermiculations 3 32 12
2 edges moderately notched 33 2 22
3 edges strongly notched and/or some dark barring or pale patches across the feather on some or all tertials 63 1 33
Second-generation scapular pattern 0 uniformly silvery-grey, darker patterning absent or very faint 0 8 0
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 0 30 0
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 0 30 0
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 17 12
4 all feathers contrastingly patterned (with dark cross bars or diamonds), lacking plain grey feathers; feather centres buffy-brown 96 15 88