Adult Herring Gull with very advanced primary moult – 20160604

This image taken on 6 June 2016 of adult Herring Gull Green YBHL shows how you can use the primary moult as and indication of its breeding status.


Note the very advanced primary moult: P1 to P4 are fully grown, P5 is 3/4 grown and P6 is half grown. Also note that the outer greater coverts are also missing, thereby exposing the white bases of the secondaries. On top of that, the striation in the neck indicates that the ‘winter plumage’ is also starting to appear.

This primary moult is about 8 weeks in advance of what is standard. Normal for this time of year is for P1 to P3 to be moulted while the primary moult that YBHL is showing is typical for the beginning or middle of August.

Here’s an image of adult Herring Gull YBRD, taken on the same day, showing a standard moult pattern with moult showing only in P1 and P2. P3 to P10 are all still present as are all greater coverts.


What does this early moult indicate?

From the very advanced moult in YBHL we can almost certainly deduce that YBHL (a female) is not breeding this year. When breeding namely, adult Herring Gulls spend most of their energy in feeding their young and will only be able to spend some energy to replace the shortest primaries P1 and P2.

The fact that YBHL is already replacing some of the larger primaries as well as the greater coverts indicates that she must have decided at an early stage that she would not be breeding this year.

Because of only very few sightings of her in the colony, we unfortunately do not have any breeding data of her to verify this, but because all known breeding Herring Gulls display a different (slower) moult pattern it is very likely that this is what is going on.

The photo was taken in the gull colony of IJmuiden where I actively record primary moult of the breeding Herring Gulls during the breeding season and it is actually the first time that I have recorded such extreme primary moult at this time of year.

2 thoughts on “Adult Herring Gull with very advanced primary moult – 20160604

  1. Hello Maarten, I’ve just read ‘Ecological Adaptations of Moult in Some British Gulls’, page 114 ( I hope YBHL started replacing her primaries so early because she had thought: ‘ I’m overfed’ and she has been moulting since that moment. Regards, Justyna C

    • Hi Justyna,

      Many thanks for pointing me to this interesting article. A few points caught my eye:

      1. “On Skokholm and Skomer many, if not most, of the adult Herring Gulls start their moult in late June or early July when they are feeding large young.”
      This is different from data collected through personal observations and from published data.
      Dutch Herring Gulls commence their primary moult early to mid-May while they are still incubating their eggs. This difference may be due to local variation and/or because the moment of commencing the primary moult has shifted forwards over the decades (similar to the egg laying date in some colonies).

      2. “The great increase in the numbers of the larger British gulls during recent decades suggests that food is plentiful.”
      This was certainly true in the 1970’s (when this article was written) and in the 1980’s, but unfortunately this is no longer the case.

      3. “[…]non-breeding birds […] can synchronise their moult with the best feeding conditions”.
      Assuming that ‘best conditions’ are no longer available, the best energy saver for YBHL would be not have to lay eggs, incubating them and subsequently feeding her young. Still, it’s all speculation and the only one who knows the real reason is YBHL…



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