April is the month in which our adult Herring and Lesser Black-backed Gulls (plus some hybrids) have returned to the colony at IJmuiden Forteiland, the Netherlands, to meet up with a partner, occupy a territory and start laying eggs.
It is therefore the month in which we start visiting the colony to do our research.
The Lesser Black-backed Gulls will have spent their winter in southern Europe or northern Africa in places such as Spain, Portugal, Algeria, and Morocco. Some will have spent their time in the United Kingdom.
The Herring Gulls will have briefly visited northern France and / or the Belgian coast, if they have left the Netherlands at all.
Many long-life partners have paired up again and have occupied the same territory that they have been using for years. Others have lost their partner or have separated from them.
Twelve adult Lesser Black-backed Gulls which are fitted with a GPS logger have also returned (more on that in a later post). The data clearly shows the territories that each bird occupies in the form of a compact cluster of data points. Three birds are an exception (in yellow, dark blue and brown): their data points are spread wider which would indicate that they do not have a partner and a territory yet. It is likely that they will not breed or start very late. See the end of this post for more information about the GPS project.
Not all birds will have made it through the winter and as we started visiting the colony on a regular basis, we again noticed the absence of familiar colour ringed birds which are not appearing. Known pairs in which both partners are colour ringed are now seen with only one bird ringed. The colour ringed partner has typically not returned but sometimes we see it not too far away in the colony: a divorce has taken place.
I have also found an adult colour-ringed Lesser Black-backed Gull freshly dead in its territory; something that we come across every year.
At the other spectrum, young (sub-) adult gulls are also appearing in the colony: some to prospect while others may start breeding. One of these is fourth-calendar year hybrid Green YCRK. It was born at Forteiland in 2018 and has colour-ringed parents YBAM and YCPL (see above). It appears to have paired up with a female Lesser Black-backed Gull and may start breeding.
It is actually very exciting for us to see the return of YCRK; we followed it closely when it grew up from a chick to a juvenile in 2018:
For more images of YCRK as a young, see this post.
On April 19 we came across the first eggs while on April 26 the first nests with a maximum of 3 eggs were found.
Male (presumed) hybrid Lesser Black-backed Gull x Yellow-legged Gull YBVA near its nest.
On very rare occasions, Herring Gull parents can still be seen with a young from last year. Such is the case with male YBMD and female YCPZ which we saw being followed by a begging 2nd-calendar year Herring Gull on April 16. Although we think that it is their only young from last year, we cannot prove it. For the record: they are not responding to its begging calls but are also not chasing it away.
Among the individuals that we are eager to see return is leucistic Lesser Black-backed Gull YAXL, now already 10 years old. We saw it for the first time on April 16:
Another personal favourite is Lesser Black-backed Gull YBJB who, sometimes, has black on all 10 of its primaries.
For more details, see the 2021 update.
What to expect in May
For most of the adult gulls, May will mostly be about incubating their eggs. Those who started early will see their chicks hatch in the 2nd week of May.
About the GPS 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.