Peter Adriaens (Belgium)
Ies Meulmeester (Netherlands)
Larus cachinnans hybrid? 4CY 6P27 May 17 2007, Łubna landfill, Poland. Picture: Ruud Altenburg.
Green 6P27. Ringed as a pullus on May 13 2004 in the mixed colony of Wisla reservoir - Wloclawek, Poland (52°39'N, 19°08'E).
This bird is a good example of the problem ageing sub-adult Caspian Gulls. There is a large proportion of 'immature' wing coverts and a white mirror on P10 seems to be absent altogether. Still green 6P27 is 4cy, ringed as pullus at Włocławek, known for its mixed breeding population (pulli registered as "Larus argentatus-complex"). The presence of so many immature patterned wing-coverts and tertials may be an indication for argentatus geneflow - normally Caspian Gull develop a mature plumage earlier that Herring Gulls do.