Larus cachinnans

(last update: February 16, 2013)

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

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cachinnans plumages

Larus cachinnans hybrid 8CY male 876P May 2004, Wloclawek Reservoir, Poland. Picture: Magdalena Zagalska-Neubauer.

Presumed hybrid male Herring x Caspian Gull, ringed as a chick in 1997 at Wloclawek Reservoir, Poland. Partial trait score of 9 (with a potential 2 points extra in case legs are short); this bird is either on the high end for Caspian but also just in the hybrid zone.

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

Here, only 8 traits are visible from the image, score so far is 9, scored by Mars Muusse (open for discussion), with theoretically another 2 points possible for (short) leg length.
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; note that the red gonys spot looks pale and this may depend on camera settings 
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) measured 2,74, Mars Muusse from photo
2 intermediate (ratio 2.0-2.39) difficult to measure from this picture, bill slightly angled
3 short and deep, well-marked gonydeal angle (ratio <2.0) 
Leg length 0 long
1 moderately long 
2 short

Fig. 6 below. Sum trait scores for adult Caspian Larus cachinnans and Herring Gulls L argentatus, and hybrids. Scores are calculated by summing individual trait score values. The figure shows the percentage of individuals in the sample with a given sum value. Numbers in parentheses are the minimum and maximum values recorded.