Lesser Black-backed Gull Green YBJB with black on all primaries, sometimes – 2021 update

It is rare to see a Lesser Black-backed Gull with black on all 10 of its primaries. But as Green YBJB of our IJmuiden Forteiland colony, the Netherlands, proves, it can depend on when you see a particular individual and which wing you’re looking at.

If you would have seen YBJB in 2017 and 2019, you would have seen it with black on all 10 primaries in both wings.

If you would only have seen YBJB in 2018 or 2020 and not in other years, you would have missed it.

If you would only have seen its right wing in 2021, you would have missed it in its left wing.

And if you would only have looked at its right wing in 2020 you would have seen that only P2 did not have black, which is even rarer.

YBJB in April 2021, showing black on all primaries in the left wing, and black on 9 primaries in the right wing. (Click for a larger view.)

I have been following YBJB since 2017 and since that time its primary pattern has varied greatly. This year, only P1 in the right wing does not have black.

The following scheme shows for each wing in the last 5 years which primaries had black, and the total number of primaries with black for each wing:

The following images show YBJB in the previous years:

YBJB-11-May-2020-IJmuiden-Forteiland-Maarten-van-Kleinwee-1
YBJB in May 2020: Left wing with black on 8 primaries (P10 – P2), right wing with black on 9 primaries (all primaries except P2, very rare).
YBJB-29-April-2019-IJmuiden-Maarten-van-Kleinwee-1
YBJB in April 2019: Black on all 10 primaries in both wings.
YBJB-14-May-2018-IJmuiden-Forteiland-Maarten-van-Kleinwee-1
YBJB in May 2018: Black on 8 primaries in both wings (no black on P1 and P2).
YBJB-8-May-2017-IJmuiden-Forteiland-Maarten-van-Kleinwee-3
YBJB in May 2017: Black on all 10 primaries in both wings.

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