Larus cachinnans

(last update: February 16, 2013)

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

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cachinnans plumages

Larus cachinnans 6CY female 740P May 2005, Włocławek Reservoir, central Poland. Picture: Magdalena Zagalska-Neubauer.

6CY female Caspian Gull Larus cachinnans, trapped in Włocławek Reservoir, central Poland, 52°39'N 19°08'E, May 07 2005, controlled at nest with eggs. This bird had been ringed as a pullus (Kiev L-002483) in Dnepr River, Kanivska GES, Cherkassy district, Ukraine, 49°46'N 31°28'E (917 km away), May 23 2000.

It shows typical characters of Caspian Gull: medium dark iris; dark orange eye-ring and gape; bill-shape index of 3.11; and characteristic pattern on outermost primary – deep, whitish tongue on inner web, subterminal black area measured at 30 mm along the shaft and a pure white tip, 63 mm long.

This Ukrainian ringed bird was trapped at Włocławek Reservoir in 2005, where a colony of some 125–130 pairs have bred since 1999 (the colony was first established in 1985). Many of these are Herring Gulls; Caspian Gulls and mixed pairs (Herring x Caspian) constitute less than half the colony, although the numbers of Caspian Gulls increase each year. The Ukranian ringed female was paired with a male Caspian Gull and laid three eggs; two young hatched successfully (on 8th and 9th May) and both were colour-ringed on 25th May. Despite intensive fieldwork, the female was not seen in 2006 or 2007, although its mate in 2005 was seen many times, apparently paired with another female.

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

Here, 8 traits are visible from the image, score so far is 6, with theoretically another 2 points possible for leg length: perfectly low score indicating pure cachinnans.
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