Larus cachinnans

(last update: February 16, 2013)

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

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cachinnans plumages

Larus cachinnans hybrid 1CY-2CY 74P1 October 2006 & March 2007, Poland & Germany. Picture: Zbigniew Kajzer & Armin Deutsch.

Green ring from Poland. Ringed as a pullus green 74P1 & metal PLG DN-19582 on May 17 2006 in Wloclawek reservoir, central Poland (52°39'N, 19°08'E). Chick followed and observed in the colony after ringing and parents assumed to be argentatus and cachinnans.

below: cachinnans hybrid 2CY 74P1 March 14 2007, Deponie Pohlsche Heide - Minden, Germany (52°23'05N, 08°46'45E). Picture: Armin Deutsch.

Pictures below: in the field very much cachinnans-like. To discuss such birds, its good to first classify it on the 'hybrid scale' according Gibbins et al, see table below pictures.

below: with argentatus.

below: cachinnans hybrid 1CY 74P1 October 21 2006, Niechorze, zachodnipomorskie, Poland. Picture: Zbigniew Kajzer.

Row of lower scapulars still juvenile.

Below, table 2 is repeated to score this bird. The scores are in italic + bold.

Overall score is 21, which places this bird within the limits of pure Caspian Gull, just outside the hybrid zone (see figure 8, repeated below this table).

Table 2. Traits and scores used to characterise birds in first-winter plumage (October-March inclusive).

 

Trait Score Description
Extent of scapular moult 0 no first-generation feathers remaining
1 a small number (<1/3) of first-generation feathers remaining
2 a significant number (>1/3) of first-generation feathers remaining
Greater-covert pattern 0 simple pattern with brown centres and sharp white edges, with no white vermiculation or notching
1 white edges with delicate notches or vermiculation; or dark brown centre with white tip to 1/3 of length (i.e. white restricted to tip or distal third)
2 clear white notches / barring creating a delicate 'piano key' pattern along the whole edge / feather; but much of feather dark
3 lots of white (more than 1/2 of coverts looking white) distributed along the whole feather, or a bold notching ('piano key' pattern)
Bill shape 0 Very long and slim, no visible gonydeal angle (L:D ratio >2.8)
1 Slim, slight gonydeal angle (ratio 2.4-2.79) Measured ratio = 2,63 by Mars Muusse from second picture.
2 Intermediate (ratio 2.0-2.39)
3 Short and deep, well marked gonys angle (ratio <2)
Leg length 0 Long and slim looking
1 Moderately long
2 Short or short and stocky
Ventral bulge 0 present
1 absent
Primary projection 0 very long (ratio >0.6)
1 moderately long (ratio 0.5-0.59) Measured ratio I/L = 0,59 by Mars Muusse from second picture.
2 medium (ratio 0.4-0.49)
3 short (ratio <0.4)
Moult: greater coverts 0 all or almost all new (>75%)
1 51-75% new
2 34-50% new
3 10-33% new
4 one or two feathers moulted
5 no moult
Moult: median coverts 0 all or almost all new (>75%)
1 51-75% new
2 34-50% new
3 10-33% new
4 one or two feathers moulted
5 no moult
Moult: tertials 0 3 or more new
1 2 new
2 1 new
3 all old
Darkness of head and body 0 totally white
1 reduced grey wash or streaking (confined to flanks and/or single streaks around nape)
2 light streaking/wash to head (incl. some dark around eye); isolated streaks/blotches on body. Overall, body looks more white than brown
3 well streaked: dark mask around eye and/or streaking covering the whole head/face; body with extensive but moderately dense streaks/mottles
4 strong and dense streaking/mottling on body and head making it appear almost wholly dark
First-generation tertial pattern 0 diffuse white tip (like Common Gull Larus canus)
1 fine pale fringe around distal portion (like classic michahellis), possibly also with some vermiculations
2 edges moderately notched
3 edges strongly notched and/or some dark barring or pale patches across the feather on some or all tertials
Second-generation scapular pattern 0 uniformly silvery-grey, darker patterning absent or very faint
1 silvery-grey background, pattern stronger than on 0, but lacks strong barring or central dark diamonds (only dark shafts and subtle anchors), with only a minority (one or two) of such feathers admixed
2 strong, contrasting shaft-streaks, anchors and/or dark central diamonds, but these more patterned feathers are less than 1/2 of all; ground colour creamy or silvery-grey, possibly with some grey feathers mixed in
3 strong pattern described in 2 on most (more than 1/2) of feathers, but possibly also one or two plain grey feathers or feathers with grey ground tone
4 all feathers contrastingly patterned (with dark cross bars or diamonds), lacking plain grey feathers; feather centres buffy-brown
     

Fig. 8. Sum trait scores for first-winter 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.