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Kleine mantelmeeuwen gevolgd met GPSloggers
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Lesser black-backed gulls tracked with GPS loggers

We have used GPS loggers, developed by Willem Bouten and team (Universiteit van Amsterdam), to follow the movements of lesser black-backed gulls in the Dutch Delta.

GPS loggers are attached to the bird rather like a backpack, which allows the batteries to charge through small solar panels on the upper part of the logger. The logger stores its position at set times throughout the day, allowing detailed movements of the birds to be attained. Data are remotely downloaded from the logger via stations that are positioned in the vicinity of, for example, the breeding colony.

This project, aimed at gathering information into the foraging activities of birds breeding in the Dutch Delta, is running alongside a long-term study at a colony on Texel (being carried out be NIOZ). We hope to establish the proportion of birds from this breeding colony that forage in the North Sea. This will provide important information as to whether these birds are potentially at risk from the effects of new offshore wind farms in the area. The (English) report can be downloaded here or via the website of the Dutch government, together with other studies carried out within the framework of the search areas for new offshore wind farms.

The fieldwork is being undertaken in collaboration with Roland-Jan Buijs from Buijsecoconsult and staff at Delta Project Management.

Research Approach

A total of nine lesser black-backed gulls were marked with GPS loggers in the colony on the Noordplaat of Krammer-Volkerak in the Dutch Delta. These loggers were developed by Willem Bouten and team at the University of Amsterdam. The logger is attached with a light harness on the back of the bird. A solar panel ensures that the battery in the logger remains charged. The positions of the loggers are saved at regular intervals, meaning that the movements of the birds can be seen in detail. The data are downloaded via a remote receiving station in the colony.

The study into breeding biology was undertaken in a section of the colony where the young could be followed.

Research Results

The main foraging areas were in Noord-Brabant and within 25 km of the colony. A few gulls foraged further than 50 km from the colony with the maximum being 120 km. The most important foraging areas were rubbish tips followed by the grassland and freshwater areas around the colony. Foraging trips to the North Sea were recorded just twice. Both cases concerned birds that had just failed with a breeding attempt.

In the pellets and remains around the colony no traces of marine prey were found. Approximately 80% of the pellets and remains were terrestrial prey, 6% freshwater prey and the rest from mixed prey. Remains of moles were also found. Remains from rubbish tips is probably underestimated as much of what is taken is digestible.

The breeding success was similar to that in other areas. Almost 90% of the eggs hatched and more that 60% of the young fledged. During the first 5-25 days the young were heavier than those on Texel. Outside of the exclosure the breeding success was lower, perhaps due to predation by rats.

The loggers seemed to have a negative effect on breeding succes with an average of 1.3 young per pair compared to 2.0 young per pair in the control group.

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