The Montagu’s Harrier breeds, rests and winters at a number of permanent spots. This was discovered by biologist Christiane Trierweiler, who tracked the birds of prey all year. The bird’s attachment to its homes may be a form of protection. Trierweiler will be awarded a PhD for her research on 29 October 2010 by the University of Groningen.
Mowing machines in Groningen that destroy their nests, African pesticides in their food, long flights over water and deserts – the life of a Montagu’s Harrier is not easy. In order to improve the protection of this endangered bird of prey, Trierweiler, together with the Werkgroep Grauwe Kiekendief (Montagu’s Harrier Work Group), has been collecting information on its breeding locations, migratory routes and winter locations. She has been following the Montagu’s Harrier on its entire yearly cycle, wherever it goes.
‘We now have 44 birds with transmitters on their backs’, says Trierweiler. This way she can remotely track the birds’ exact locations. ‘The special thing about this research is that we are combining this technology with basic fieldwork’. For example, Trierweiler and her colleagues drove many kilometres through African fields to find the Harriers’ sleeping locations, and collected pellets in order to analyze eating patterns. Satellite transmitters were distributed from the Netherlands to Eastern Poland and Belarus. A large number of researchers and volunteers helped with the international project.
Trierweiler’s elaborate research led to a number of important discoveries. One of these was that the Montagu’s Harrier returns to the same collection of homes. It breeds at a number of locations throughout Europe, including Oldambt in Groningen. After the breeding season it flies to familiar locations in Africa to spend the winter there. ‘We followed a female for three years and saw that she kept returning to the same locations, in areas of 50 by 50 kilometres’, says Trierweiler. Though the Montagu’s Harrier will move its breeding areas from time to time, it appears to be loyal to its winter locations. ‘We thought that it would be more flexible in the winter, when it has no nest. But apparently that is when it likes familiar areas'.
The female that Trierweiler followed had three fixed winter locations that she returned to every year. One of these was immediately after the Sahel, at the first green area she encountered after the long flight. Before Trierweiler’s research it was assumed that the Harrier would then migrate with migratory grasshoppers. But even in years without migratory grasshoppers, the birds follow the same route. Analysis of pellets revealed that the Harriers eat non-migratory grasshoppers, as well as birds and reptiles. ‘They migrate from North to South and remain exactly in the zone where there is the most food at a particular time’.
The Montagu’s Harrier’s loyalty to certain areas makes it easier to protect its habitats. For example, by ensuring that only organic pesticides are used in these areas, we can protect the bird of prey from poisoning. In Europe it is possible to actively search for nests in order to stop them from being destroyed by the blades of mowing machines. ‘If a nesting female is killed, any reproductive contribution she may have had is also wiped out’, says Trierweiler. Moreover, agrarian nature conservation in breeding areas has made it easier for parents to find enough food for their offspring in intensely farmed areas like East Groningen. This contributes to population growth.
Trierweiler conducted her research on the initiative of the Stichting Werkgroep Grauwe Kiekendief (Montagu’s Harrier Work Group). This foundation from Scheemda aims to protect the bird of prey. ‘It is necessary, as in 1987 there were only two pairs left in the Netherlands. There are now around 50’, says Trierweiler. ‘The Montagu’s Harrier is a wonderful, elegant bird. Also, as a predator at the top of the food chain, it is a good indicator of the condition of the ecosystem. If things are going well with the Montagu’s Harrier, the ecosystem at that location is in good condition'.
The end of her PhD research does not mean the end of Trierweiler’s research on the Montagu’s Harrier. During the research she learned a lot about the Harrier's migratory routes. Among other things, she discovered that many Montagu’s Harriers rest in the same area of Eastern Morocco. Trierweiler made two trips to that area this year. ‘Not much is known about how birds of prey keep their energy levels up during long treks. I want to find out more about that’.
Christiane Trierweiler (Germany, 1978) studied biology at the University of Groningen. She conducted her PhD research at the University of Groningen Department of Animal Ecology, the Institute of Avian Research ‘Vogelwarte Helgoland’ and with the Stichting Werkgroep Grauwe Kiekendief. Since April 2010 she has been continuing her research as a postdoc with the same organizations. Trierweiler will be awarded a PhD in Biology, and her supervisors were Prof. J. Komdeur and Prof. F. Bairlein. Her thesis is entitled Travels to feed and food to breed - The annual cycle of a migratory raptor, Montagu's harrier, in a modern world.
More information: Christiane Trierweiler, tel. 050-363 7852, e-mail: christianetrierweiler yahoo.com.
Photographs of the Montagu’s Harrier are available through the PhD candidate.
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