Radar for monitoring birds on the Wadden Sea
This autumn, some ten to twelve million migratory birds will pass through the Wadden Sea area on their journey as they did last spring. The magnitude of this migration makes the Wadden Sea one of the most important nature reserves in the world. The area has been included on the United Nations World Heritage List since 2009. It is vitally important that the migratory birds are left to rest and forage on the mud flats undisturbed. However, we know very little about their flight paths and where they find their food. Researchers from the IMARES institute for coastal and marine research, which is part of Wageningen UR, monitor the birds’ flight, rest and forage movements continually from a distance using video cameras and mobile bird radars. The information they acquire will be used to improve and enhance the way the Wadden Sea is managed. It will also make it possible to coordinate management of the space allowed for migratory birds on the one hand, and activities such as fishing and recreation on the other. In this way, Wageningen UR is helping to improve the quality of life.
Eurasian oystercatchers on the mud flats
IMARES research
To provide adequate protection for Wadden Sea birds, it is important to find out where, what and how much they eat on the mud flats. Shellfish and worms in the bed of the flats form the main source of nutrition for these birds, but some areas of the mud flats provide very little food and some sources are only available at certain times of the year. Although we can keep track of how many birds live and stop off in the Wadden Sea area, we do not know exactly where the various species of birds find their food. This is due to the tidal influence of the Wadden Sea. The variations in sea level cause constant variation in the distribution of birds. Another factor is the huge seasonal difference in numbers and distribution.
Allowing people onto the mud flats to monitor and record this ever-changing distribution would obviously disturb the birds. Another problem is that monitoring is only possible in good weather and it is just as important to find out where birds forage during bad weather when conditions become more difficult for them. Furthermore, we cannot watch birds at night. This is a problem as the mud flats are sometimes exposed at night, and birds therefore forage for food both at night and during the day.
Bird radar
To study the birds’ flight behaviour, we use a bird radar: the Robin Bird Radar. This radar has highly specialised software that allows us to pinpoint birds in flight. A radar sees a bird as a ‘bag of flying water’. This particular radar filters moving objects from all the other reflections it receives, thereby allowing it to track the ‘flying bags of water’. The Robin software therefore shows the flight paths of the birds it picks up.
Partners in research
Martin Baptist from IMARES is heading this research, which is being funded by the Netherlands Organisation for Scientific Research. The project is being carried out in association with SOVON Dutch Centre for Field Ornithology, the University of Amsterdam, Bureau Waardenburg, Robin Radar Systems, TNO, Outersight Ltd., EcoCurves and the Royal Netherlands Institute for Sea Research.
Radar image from the bird radar. The pale blue lines show the flight paths of birds flying over Balgzand.
The bird radar is aimed to cover the area across Balgzand, a complex of mud flats between Den Helder and Den Oever (Texel). The radar itself has been set up on Royal Marine territory (see Alle Hens, June 2010). Birds search for food at low tide when the flats are exposed, and rest at high tide. We track the flight movements of Wadden Sea birds seven days a week, 24 hours a day allowing us to monitor the exact timing of flight behaviour in relation to the tide cycle, day/night, weather conditions and seasonal changes. An important part of the survey is ascertaining the distance at which the radar is able to identify individual birds or groups of birds. To test this, we carry out verification counts: a group of observers record which birds they have seen flying, the numbers of these birds and the route and height at which they were flying. The information collected is then compared with the flight path data on the radar. We have also fitted GPS transmitters to the backs of five oystercatchers. We therefore know exactly where and how these birds have flown, and we check this information against the flight paths recorded by the radar. This shows us the maximum distance at which the radar can track the oystercatchers, and the extent to which this depends on the direction they take.
Flight paths of oystercatchers with transmitters above Balgzand.
Video camera
A tall pole fitted with a video camera has been set up in the middle of the mud flats. This camera records high-resolution video images, better than HDTV. It has also been fitted with infrared lamps so that we can identify birds at night at distances of up to 200 m. LED lamps have been used in order to save energy, as there is no mains electricity nearby. The power is supplied by solar panels during the day and fuel cells at night. All the images are transmitted to IMARES Texel, eight kilometres.
The high-resolution video camera with IR-LED lamps.
The video camera allows us to monitor the foraging birds seven days a week, 24 hours a day. Sixteen sectors have been marked out around the camera, and the camera films each sector automatically every 30 seconds. The camera´s location was chosen in order to monitor a range of environments. There is a muscle bank close to the camera, a high sandy ridge, a medium-high section with sand/silt and a lower silty area. Samples of the various species living in the sections are taken for examination on a regular basis. The availability of various sources of food and the length of time the mud banks are exposed help to determine the types and numbers of birds that feed there.
Our ultimate aim is to compile all the data on flight and foraging movements into a single model. The model can be used to make predictions about where and when the birds will stay for the entire Wadden Sea area. In turn, this will form the basis for well-considered management in the Wadden Sea.
Partners in research
Martin Baptist from IMARES is heading this research, which is being funded by the Netherlands Organisation for Scientific Research. The project is being carried out in association with SOVON Dutch Centre for Field Ornithology, the University of Amsterdam, Bureau Waardenburg, Robin Radar Systems, TNO, Outersight Ltd., EcoCurves and the Royal Netherlands Institute for Sea Research.
Night-time image of foraging oystercatchers.