Each spring about 200,000 Brent Geese depart from England and France to the Siberian tundra to breed. En route they descend on salt marshes and polders in the Wadden Sea area to eat young grass. Farmers noted that geese seemed to have a preference for grasslands with short vegetation. STW researchers at the University of Groningen havenow discoveredthe reasons for this. The ecologists measured the preference of the geese for small experimental areas. Some areas had little grass and others had much. Some areas contained a high protein level (a measure of the nutritional quality) and some a low level. The biologists studied the behaviour of the birds and counted the number of droppings on each trial area. From the droppings, the time spent by the geese in an area could be determined, as geese produce droppings at very regular intervals. The study revealed that geese prefer grass areas where the rate of protein ingestion is the highest.
That is the case for short grass, as in general this has a high protein level. Furthermore, Brent Geese find it easier to eat short grass than long grass. Grazing livestock can help to keep the grass short when its growth is particularly strong, as is the case in spring. If the geese are not chased away, they regularly return to the same area. By doing this they keep the grass short and thus maintain the quality of their own food. A policy in recent years of tolerating geese in certain agricultural areas along the Dutch Wadden Sea coast has therefore been favourable for the geese, as they prevent the grass from becoming too long. The preference for short grass also means that the natural vegetation succession on salt marshes poses a serious threat for the geese. The undisrupted growth of salt marsh vegetation results in plants which are attractive for the geese being displaced by plants which are inedible. In this situation, the livestock are also an ally of the Brent Geese. Grazing cows, sheep and horses prevent the salt marsh vegetation from becoming too coarse.
Further information can be obtained from Daan Bos (Department of Plant and Animal Ecology, University of Groningen, now at Altenburg en Wymenga), tel. 31-503-119-691 (home), e-mail d.bos@altwym.nl. The thesis will shortly be available at www.ub.rug.nl/eldoc/dis/science/d.bos/. The defence of the doctoral thesis will take place on 25 October 2002. Mr Bos' supervisors are Prof. J.P. Bakker and Prof. R.H. Drent.
The research was funded by the Netherlands organisation for Scientific Research (NWO).
(Photo) Brent Geese prefer short grass. This is because the rate of protein uptake by Brent Geese decreases as the quantity of available food increases.