5CY Herring Gull YCKL with sub-adult plumage – 20210412

Images of European Herring Gull Green YCKL in its fifth calendar year, but showing a fourth-calendar year plumage: much brown on the wing coverts, primaries, and tail, and much black on primary P5.

This reminded me of 2020 when it showed the plumage of a third-calendar year when it was in its fourth calendar year: much brown in the primaries and secondaries, a distinct tail band, and no white in the primaries.

Its plumage therefore has been a year behind what is expected to be seen in a Herring Gull of that age.

YCKL was ringed by us as a pullus in 2017 in the IJmuiden Forteiland colony, the Netherlands, and we therefore know its exact age.

I have not come across many birds that show such a retarded plumage, but it does mean that ageing sub-adult Herring Gulls can be tricky when they are not ringed and their exact age is not known.

I took the following images on 12 April 2021:

Compare the above image of YCKL as a 5th-calendar year in April 2021 with the image below of YCKL as a 4th-calendar year that I took in May 2020:
Above: YCKL in May 2020 as a 4th-calendar year with the plumage of a third-calendar year, IJmuiden Forteiland, the Netherlands.
Above: YCKL in May 2020 as a 4th-calendar year with the plumage of a third-calendar year, IJmuiden Forteiland, the Netherlands.

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