Larus cachinnans

(last update: February 16, 2013)

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

Home

cachinnans plumages

Larus cachinnans hybrid 2CY 92P1 January 19 2007, Deponie Pohlsche Heide - Minden, Germany (52°23'05N, 08°46'45E). Picture: Armin Deutsch.

Green ring from Poland. Ringed as pullus green 92P1 & metal PLG DN-19558 on May 14 2006 in the mixed colony of 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.

This bird is very Herring-like and has a high score (30). Notched pattern on GC, transversal bars, even on very fresh lower scapulars, streaked head, rounded head shape all indications for argentatus. Although obviously very much argentatus, some influence of cachinnans apparent as well; like small eye and weak gonydeal angle, dark outerwebs of inner primaries and extensive moult in underparts and head. To discuss such birds, its good to first classify it on the 'hybrid scale' according Gibbins et al, see table below pictures.

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

Overall score is 30, which places this bird in the hybrid zone of the spectrum, but also within the limits of pure Herring Gull (see figure 8, repeated below this table). Bill measurements have a relatively high error as the image is slightly out of focus (still, trait score "2" for this bird seems reasonable).

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)
2 Intermediate (ratio 2.0-2.39) Measured ratio = 2,39 by Mars Muusse from second picture.
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 = 0,53 by Mars Muusse from last 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.