Larus cachinnans

(last update: February 16, 2013)

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

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cachinnans plumages

Larus cachinnans 10CY male 802P April 29 2006, Włocławek Reservoir, central Poland. Picture: Magdalena Zagalska-Neubauer.

10CY male 802P, ringed as chick in 1997, April 29 2006 Wloclawek - Vistula river, Poland. Bird to show variation of wing-tip of adult Caspian Gulls at the mixed colony at Włocławek Reservoir, central Poland. Birds are included only if all characters are within known cachinnans variation, to ensure that influence of argentatus (possible hybrids etc.) is minimal or lacking. All birds were trapped at nests during incubation. If there are photos of the same bird from different years, they are presented side by side.

Below, table 1 is repeated to score this bird. Not all traits can be scored, the partial scores are in italic + bold.

Here, only 5 traits are visible from the image, score so far is 3, with theoretically another 10 points possible.
Trait Score Description
P10 overall pattern: white to black ratio 0 less black than white
1 approximately equal black and white
2 more black than white
P10: white tip 0 clear white, no signs of black
1 small dark spots on one or both webs
2 incomplete subterminal bar (two large black spots, one on each web or an unconnected bar, broken in the middle)
3 complete subterminal bar
P10: tongue 0 white or whitish
1 paler than mantle
2 same shade as mantle
P5: extent of black 0 black on both webs connected, forming band, black of equal depth on each web
1 black on both webs connected, forming band, black on outer web deeper than inner
2 black on both webs, but isolated spots (= incomplete bar)
3 black on outer web only
4 no black
P4: extent of black 0 black on both webs
1 black on one web only
2 no black
Iris peppering 0 dark-looking, >50% covered by dark spotting/peppering
1 moderately dark, with 10-50% of the area spotted
2 single or very few dark spots (area < 10%)
3 no dark spotting on iris
Eye-ring colour 0 dark/deep orange to red 
1 pale to moderately orange 
2 yellow
Bill shape 0 very long and slim, with little/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 gonydeal angle (ratio <2.0) 
Leg length 0 long
1 moderately long 
2 short