Images taken during a visit to the gull colony of IJmuiden Forteiland, the Netherlands, on March 29, 2019, as part of our research project.
Shown are European Herring Gulls, Lesser Black-backed Gulls, and (presumed) hybrid Lesser Black-backed Gulls x Yellow-legged Gulls.
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European Herring Gulls
Male YBMD with female YCPZ
Male YCKZ with female YCHL
Lesser Black-backed Gulls
(Presumed) Hybrid Lesser Black-backed Gulls x Yellow-legged Gulls
Now in its 5th calendar year. Note the sub-adult markings in the upper and lower wing.
Compare with the images as a 4th-calendar year.