The picture below is of Dutch European Herring Gull YDAP, seen on April 29, 2024, showing the primary pattern of its left wing.
The primary pattern in the inset looks very different but is of the same bird from 2020… (click for a larger view)
Note the large differences in the pattern on P10, P9, P6, and P5, as outlined below:
| Primary | 2024 | 2020 | |
| P10 | White tip with a small black notch | Broken band | |
| P9 | The faintest hint of a mirror (not noticeable in the field) | A distinct mirror on the inner web | |
| P6 | Black on the outer web only | Black on the inner and outer web | |
| P5 | Small mark on the outer web | Distinct mark on the outer web |
We ringed YDAP as an adult male in May 2020 in the IJmuiden Forteiland colony, the Netherlands. All images were taken at that location by me (click for a larger view).
When checking images of the intermediate years (see below), a mix of this pattern can be seen:
| Primary | 2024 | 2023 | 2022 | 2021 | 2020 |
| P10 | White tip with a small black notch | White tip with a small black notch | White tip with small black notches | No data | Broken band |
| P9 | The faintest hint of a mirror (not noticeable in the field) | A distinct mirror on the inner web | A small mirror with soft edges on the inner web | No data | A distinct mirror on the inner web |
| P6 | Black on the outer web only | Black on the inner and outer web | Black on the outer web only | No data | Black on the inner and outer web |
| P5 | Small mark on the outer web | A distinct mark on the outer web | A distinct mark on the outer web | No data | A distinct mark on the outer web |
YDAP in March 2023:
YDAP in April 2022:
YDAP in May 2020 during ringing:
I have been following the primary patterns in our colour-ringed Herring Gulls from some years now, and this is the largest change that I have yet recorded. The lack of the distinct mirror on P9 in 2024 and the changes on P6 are especially striking to me.
This very interesting development shows once more how much the primary pattern in an individual can change and how difficult it is to say anything meaningful about the primary pattern of an individual when it can change so drastically over different moult cycles. It very much depends during which moult cycle a bird is observed.
Other striking examples that I have recorded mostly revolve around the inner primaries P4 and P5, as can be seen in YDBM and YBUF.
Gulls to the Horizon 
Very interesting Maarten, and a testimony to your dedication! It is particularly interesting that in this case that while generally, the extent of black is receding, the mirror on p9 has also disappeared.
Thank you for your efforts!
Killian Mullarney
Thanks for your comment and kind words Killian! The disappearance of the mirror is very interesting indeed, as is the change in the amount of black on P6. It would not surprise me though when the mirror on P9 and the black on the inner web of P6 appear again in a subsequent moult cycle, based on the changes that individuals such as YDBM and YBUF showed.
Hopefully we can continue to follow YDAP over the coming years and keep documenting its primary pattern.
Best regards,
Maarten