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| Coordinator: Greg Neubauer Marcin Przymencki Albert de Jong Mars Muusse 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. |
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| 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 | ||
Larus cachinnans