Adult Lesser Black-backed Gulls and the presence or absence of a mirror on P9 are sometimes a topic of discussion.
Green YCKB from our Dutch IJmuiden project proves that answering that question depends on a) in which year you come across such a gull (or more precisely: during which moult cycle), and b) which wing you look at:
- YCKB has no mirror on P9 in the right wing but does have one in the left wing in 2019 (top image)
- YCKB had a mirror on P9 in the right wing as well as in the left wing in 2018 (middle and bottom image)
Click for a larger view.