One of the most fascinating aspects of primary moult in adult European Herring Gulls for me is the phase in which they suspend their moulting process for a certain period of time.
For some gulls this means that they don’t start their moult when the majority commence their moult, but wait until July – well into the breeding season. For others it means that they do start when all others start but only replace P1 or P1 and P2 while leaving all other primaries in place. These individuals then commence their moult at the end of June or the beginning of July.
Little is known about this phenomenon for this species but we are in the privileged position to study it in detail in the IJmuiden Forteiland colony in the Netherlands. For more info, see Suspended primary moult in adult European Herring Gulls Larus argentatus argenteus of the Dutch colony of IJmuiden Forteiland.
While scoring the primary moult for 40 gulls photographed on 17 June 2019, 20 showed suspended moult, 3 showed resumed moult, while 17 showed a regular moult pattern.
Below are some examples (click for a larger view).
P1 or P1 and P2 are replaced, all other primaries are present.
Inner primaries growing or replaced with the next primary missing.