Wetenschap - 15 november 2001

On the look out for birds with a tape recorder

On the look out for birds with a tape recorder

Ruud Foppen's passion is marshland birds that breed in wet areas like the Netherlands and the African Niger delta. He carried out research in these reedlands, to identify the dangers the birds face.

In previous summers, early in the morning, Foppen could be found deep among the reeds along the shores of the IJsselmeer, in the north of Holland. Quietly entering the reeds in a boat, he held his tape recorder ready and played a cassette, filling the damp air with a recording of the song of a great reed warbler. Karrekarrekeetkeet! Foppen looked around with the utmost concentration, expecting real birds to arrive. After some time they came and Foppen caught them with an almost invisible net. He ringed the birds so that he could track them closely after he released them.

"These birds just love their own singing," says Foppen. "I play a song of a bird that I recorded earlier, which makes the birds in the reeds really wild. They think a competitor has arrived when they hear my tape." In this way the biologist managed to catch more than 150 reed warblers. The birds are given rings around their legs, "Red, green, blue and other coloured rings, making it possible to identify them later with my telescope and binoculars."

After years of hard work in the reeds, together with a number of co-workers, Foppen found out that the young birds need an area of nature about ten by ten kilometres. "These birds need large protected areas to survive. In the Netherlands, we have to create more of these, our natural areas are too fragmented." Foppen points out that the Netherlands has been a very important breeding ground for birds in Europe for a long time. "We have to keep it this way. But we see that numbers are declining rapidly."

The reasons are manifold. It is not only that natural areas are shrinking, pollution also continues to threaten birds along European coasts and lakes. What's more, environmental changes in other continents are threatening the birds in Europe. "Many marshland birds escape the Dutch winter and fly all the way to the Niger Delta in Africa. There however, the birds have fallen victim to extreme droughts in the past years. The result is that fewer birds return to Europe, and there is the worrying possibility that climate change will even make droughts more frequent."

Hugo Bouter

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