First visit to IJmuiden Forteiland colony of 2021 season and returning birds with GPS loggers

It’s April and over the last few weeks we have enjoyed seeing the return of the first Lesser Black-backed Gulls that breed in the colony at IJmuiden Forteiland, the Netherlands. They have left their wintering locations in southern Europe and North Africa and are joining the Herring Gulls which have already returned since the beginning of January after spending their winter in France, Belgium, and the Netherlands. Many Lesser Black-backed Gulls are still arriving on a daily basis.

For us as the research team it means that our season of visiting the colony to do field work is also starting. We had our first visit to the colony on March 29 and will start visiting the colony on a regular basis very soon.

As is the case each year, it is very exciting to discover which of our birds will return and who they will pair up with. It is great to see that many partnerships are re-established and that new ones are being created. By being able to follow our colour-ringed birds individually, we feel that we really know them well and know how they behave and where they will occupy a territory.

The group of returning Lesser Black-backed Gulls also contains individuals that are fitted with a GPS logger as part of a project of the University of Amsterdam. Eight individuals have already returned and it is exciting to find out where they have been and what they will do during the upcoming breeding season. More on this below, but first some general images that I took during our visit.

The bird in the centre with the lighter grey mantle is Green YAHH, a presumed hybrid Yellow-legged Gull x Lesser Black-backed Gull. Its mantle is actually a much lighter grey, as can be seen in the next photo.
Presumed hybrid Yellow-legged Gull x Lesser Black-backed Gull YAHH landing in its territory while mew-calling.
Female Lesser Black-backed Gull YCPL with partner YBAM, a presumed hybrid Yellow-legged Gull x Lesser Black-backed Gull. They have been a pair for at least four years.
One of the high-lights of our visit was seeing 4th-calendar year YCRK, an offspring of Lesser Black-backed Gull YCPL and YBAM, a presumed hybrid Yellow-legged Gull x Lesser Black-backed Gull (see above). It stood some 30 meters from the place where it was born. I am hoping that it will keep visiting the colony so that I can take some better photos of its plumage.
A new Herring Gull pair with YBWF on the left and YCKL on the right. YCKL is an interesting 5th-calendar year with a very sub-adult plumage, as can be seen in the next photo.
Fifth-calendar year Herring Gull YCKL with a very sub-adult plumage: much brown in the coverts, much black on P5, and black in the tail.

GPS project

Of the various adult Lesser Black-backed Gulls which have been fitted with a GPS logger over the last 2 years (see About the project below), 8 have now returned.

As we noticed last year, they very quickly return to their daily schedule of visiting their favourite foraging locations in and around Amsterdam and out to the North Sea.

The data that has been stored during the winter in the logger that they are carrying is currently being downloaded and we are looking forward to discover what journeys this will reveal.

Lesser Black-backed Gull YAVH showed itself well during our visit to the colony on March 29, 2021. The logger was fitted last year so we will see for the first time in detail where it spends the winter.
In rest, you can hardly tell that YAVH is fitted with a logger.
Lesser Black-backed Gull YDBJ was originally ringed as YAAX as an adult in 2008 but fitted with a new ring and logger in 2020.
A screenshot from the uva-bits website, showing the tracks of the 8 returning birds (click for a larger view). Foraging trips are typically to the East (suburban areas such as Amsterdam) and to the West (the North Sea). Exception is YDAV/5576 in blue which has made a trip to the south of The Hague.
A closer view of the GPS tracks in the colony. Clear to see is the territory that each of the individuals occupies. Exception again is YDAV/5576 in blue which does not seem to have a fixed place yet. Together with its trip south this could be an indication that it has not found a partner yet and that it may not breed this year. We will monitor its progress during the coming weeks.

About the project


The tracking study is part of an ongoing collaboration between the University of Amsterdam UvA (Dr. Judy Shamoun-Baranes) and the Royal Netherlands Institute for Sea Research NIOZ (Dr. Kees Camphuysen).

The study is being conducted within the project “Interactions between birds and offshore wind farms: drivers, consequences and tools for mitigation” funded by NWO Applied and Engineering Sciences Open Technology Programme, Rijkswaterstaat and Gemini windpark.

The tracking study will provide complementary information on the movement patterns of gulls breeding along the North Sea coast, with similar objectives to the studies conducted on Texel and Schiermonnikoog.

The main aim is to identify intrinsic and external drivers of movement from fine scale flight behaviour to seasonal migrations. While adult gulls from other colonies have been tracked since 2008, little is still known about the daily movements and flight behaviour of juveniles and how this differs from adults.

This study will contribute to our knowledge on how juvenile birds develop their foraging and migration strategies and how their flight behaviour differs from adults.

2 thoughts on “First visit to IJmuiden Forteiland colony of 2021 season and returning birds with GPS loggers

  1. I love reading your detailed reports about individual gull feather markings.
    I tried to instigate a ringing project for Juvenile Herring Gulls as we need to identify local gulls to improve their welfare. Often they suffer from cruelty from local people who regard them as pests. The head of the rescue, who take in the most young, stated that leg rings cause entanglements. Have you ever had problems with the leg rings?

  2. Hi Dawn, thanks for your comment and for looking after your local Herring Gulls. Much appreciated.

    To answer your question: no, leg rings do not cause entanglements. However, it is imperative that they are fitted correctly by a licensed ringer. A metal ring should fit tightly with no overlap or gap, and colour rings can best be glued. We have had no problems with entanglements.

    Should you start a ringing project, you might want to consult the BTO (, and if you’re thinking of using colour rings, make sure to coordinate this so that it does not clash with any existing projects. For details, see European Colour Ring Birding at

    All the best!



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