Larus cachinnans

(last update: February 16, 2013)

Peter Adriaens (Belgium)
Ies Meulmeester (Netherlands)


cachinnans plumages

Larus cachinnans hybrid 5cy male 170P April 2009, Włocławek Reservoir, central Poland. Picture: Grzegorz Neubauer.

Male 5CY hybrid Caspian x Herring Gull, Wloclawek, central Poland, April 2009. Mother known as (yellow-legged) Herring, father as Caspian. Ringed as chick in Wloclawek, May 2005. Not all hybrids appear intermediate between their parent species: notice this bird’s striking resemblance to a Yellow-legged Gull. Its P10 pattern excludes Caspian (more black than white; see table 3), while its structure has intermediate scores between Herring and Caspian. Its overall score is 14 ( this might also be 13, see table below), higher than that of any pure Caspian (which has a maximum of 12). This individual was discussed in Neubauer et al. (2010).

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

Here, all 9 traits are visible from the image, trait score is 14, which places this bird in the hybrid zone.
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) measured 2,43.
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