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 3. Percentages of sample adult birds with scores for selected plumage, structural and bare-part traits.

Trait Score Description Herring
(n=132)
Hybrid
(n=12)
Caspian
(n=100)
P10 overall pattern: white to black ratio 0 less black than white 39 25 100
1 approximately equal black and white 31 25 0
2 more black than white 30 50 0
P10: white tip 0 clear white, no signs of black 36 25 54
1 small dark spots on one or both webs 44 42 31
2 incomplete subterminal bar (two large black spots, one on each web or an unconnected bar, broken in the middle) 14 8 3
3 complete subterminal bar 7 25 12
P10: tongue 0 white or whitish 2 17 76
1 paler than mantle 37 25 24
2 same shade as mantle 61 58 0
P5: extent of black 0 black on both webs connected, forming band, black of equal depth on each web 2 25 1
1 black on both webs connected, forming band, black on outer web deeper than inner 7 42 7
2 black on both webs, but isolated spots (= incomplete bar) 20 8 14
3 black on outer web only 27 25 77
4 no black 44 0 1
P4: extent of black 0 black on both webs 0 0 1
1 black on one web only 1 17 27
2 no black 99 83 72
Iris peppering 0 dark-looking, >50% covered by dark spotting/peppering 0 0 47
1 moderately dark, with 10-50% of the area spotted 2 9 27
2 single or very few dark spots (area < 10%) 17 33 26
3 no dark spotting on iris 81 58 0
Eye-ring colour 0 dark/deep orange to red  6 57 21
1 pale to moderately orange  27 36 79
2 yellow 67 7 0
Bill shape 0 very long and slim, with little/no visible gonydeal angle (L:D ratio >2.8)  0 8 0
1 slim, slight gonydeal angle (ratio 2.4-2.79)  8 42 87
2 intermediate (ratio 2.0-2.39)  59 25 13
3 short and deep, well-marked gonydeal angle (ratio <2.0)  33 25 0
Leg length 0 long 5 42 52
1 moderately long  50 42 46
2 short 45 17 2