A few weeks ago, 10 adult Lesser Black-backed Gulls from our IJmuiden Forteiland colony were fitted with a GPS logger. Time therefore to look what the data has shown us so far.
Photo above: Lesser Black-backed Gull Green YBKW fitted with GPS logger #5861. IJmuiden Forteiland, the Netherlands, June 2019.
Image above (click for a larger view): GPS-tracks of all 10 gulls over a period of 3 days in June. Each color is a different gull, each dot is the moment data was logged. Note Amsterdam on the right, the North Sea on the left, and the colony on the coast where all tracks merge.
How it works
First of all a summary of how it works.
The GPS loggers are fitted on the gull by means of a back-pack. At intervals of 5 minutes (and in some areas 5 seconds), data is logged such as the coordinates, date, time, speed, elevation, and more. These intervals can be controlled remotely. This data is stored on the device until the gull is in the vicinity of a receiver, at which time the data is downloaded. The logger is powered by solar cells which take up most of the size of the logger.
During the breeding season, the data is regularly downloaded. Data of the last 3 days can be viewed online.
When the gulls leave the colony at the end of August and migrate to their wintering locations in southern Europe and northern Africa, the data stays on the logger until they (hopefully) return to the colony when the data will be downloaded again.
So what has all the data over the past few weeks shown us? Here are some of the main points.
When researching gulls, it becomes apparent quite quickly that each gull is an individual with its own character and behaviour.
The GPS tracks of the 10 gulls illustrate this beautifully (see the image above): all 10 have their own daily routines and very regularly visit a particular location (different from the others) by following pretty much the same route. These same journeys can be seen day after day.
They do this for a reason: they will have learned that some type of food is available at that location and rather than checking out other locations with the risk of not finding any food, they choose the security of visiting the same place over and over again.
If you want to see a particular gull therefore, you have to visit a particular place (something that ring readers will be very familiar with).
We see for example that YASV mainly visits the city of Hoofdorp, that YCVL is extremely faithful to a site in Amsterdam, YCVM prefers the city of Haarlem, while YBJC almost daily visits the Erasmusgracht in Amsterdam.
Below is the favorite location of YCVL: the area around the Burgemeester van Tienhovengracht in Amsterdam (click for a larger view):
One of the things that surprised us most when seeing the data come in for the first time was that the 10 gulls are very urban in their food selection. All 10 visit cities in the surrounding area with 8 (!) going to Amsterdam, one to Hoofddorp (near Schiphol airport), and one to Haarlem (close to the colony).
This confirms once more that cities are an important source of food (and that humans are messy).
It also confirms that the gulls that people see fouraging in their street are not necessarily the gulls that are breeding on their roofs, but (also) the gulls that have their nest many kilometers away. (In other words: dealing with the local roof breeders won’t solve a local gull problem. For more about this phenomenon, see this article on Grote Meeuwen in de Delta.)
At the same time, trips far out to sea are also made. This is likely related to having to find energy-rich food to feed the chicks with. (One exception is YAVL who interestingly has not made any fouraging trips out to sea yet, even though it currently has 2 chicks to feed.)
YBJC for instance regularly visits the Erasmusgracht in Amsterdam where on a very regularly basis food such as bread and pizza is disposed of by the locals, but has also been making very elaborate trips out to the North Sea to catch fish. At the time of writing, YBJC has 3 chicks to feed.
Above: tracks of YBJC showing trips to Amsterdam and to the North Sea.
Above: YBJC at the Erasmusgracht in Amsterdam.
When looking at the area in which our IJmuiden gulls operate, we see that it is a much smaller area than for example that of comparable gulls from the Texel colony. Those operate much further to the south and west:
After only a few weeks, our 10 gulls have given us much insight into their daily lives. It is an exciting period for them: some have already lost their eggs or chicks, while others face the challenge of having to raise 3 chicks. It is fascinating for us to follow them this way during this important part of the breeding season.
To be continued…