Duck Stop

260,000 water birds in search of food

As many as a quarter of a million water birds spend the winter on Lake Constance, as monthly counts through the winter half year have shown. Of course, that many birds need a lot of food, so the winter visitors play a significant role in the lake’s ecosystem. For instance, in the winter there are almost no low-light algae to be found down to a depth of two metres, because they are almost all devoured by the water birds in some places. Low-light algae, very primitive water plants found world-wide, are a type of green algae that cover large expanses of the bed of Lake Constance. A few individuals of some bird species that spend the winter at Lake Constance – such as the Eurasian coot, the red-crested pochard and the tufted duck – also stay on the lake until the breeding season and into the summer half year. Finally, after the breeding season, they gather in sheltered places to moult. While moulting, when they renew their feathers, water birds are unable to fly, so they often hide in the reeds at the water’s edge. This means that they have to find places where they are not only protected from predators, but where they can also find enough food in the water.

One of the goals of this project, apart from studying the water birds that spend the winter on the lake, is therefore to discover how the food is distributed amongst the bird population in the summer months and what effect this has on the overall ecosystem of Lake Constance. To find this out, the researchers are addressing questions such as if and how the composition of their food changes over the course of the year, what preferences specific species have, or whether there are differences between male and female birds.

They are using a number of different methods to address these problems, for example: Analysis of stable isotopes, analysis of the stomach contents and faeces and by running experiments with foraging protection cages. Then the data from different seasons is compared, for example from the breeding season, the moulting season and the winter. The researchers expect the feeding preferences of the various bird species to differ and for them to seek out different foraging grounds over the course of the year to access different sources of food. One of their assumptions is that male and female birds have different preferences.
Another thing that the project is looking at is the effect that the birds’ foraging rate has on the amount of water plants in the lake.

This project is part of Collaborative Research Centre 454 “Littoral of Lake Constance” at the University of Konstanz and is scheduled to last from August 2007 until June 2010.
Project associates:
Dr. Petra Quillfeldt (project leader), Dr. Hans-Günther Bauer (project leader);
Anja Matuszak (doctoral researcher)





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