Solving the mystery of the thinning egg shells and other conservation whodunnits

January 28, 2000

As extinction rates explode, Cambridge University is seeking to set up a professorship of conservation of nature. Pauline Hunt reports

From Anglo-Saxon times to the Middle Ages, villagers near a Norfolk lake would lay their bundles of hemp (known to us as cannabis) to winter under the water. The chemicals produced gave off noxious fumes and the water became poisonous to cattle and humans, but the process enabled the fibres to be separated to make rope and linen the next year.

What no one knew, until the new discovery by a young Cambridge scientist, David Horne, is that the chemicals had a devastating effect on the life of tiny molluscs as well as ostracods (minute crustaceans) living in the lake. The number of these creatures, now back to normal, fell disastrously during those centuries.

The discovery was a chance find after Horne bored down 12m to extract a deep core of lake sediment carefully preserved in its original layers, in order to research climate change over the past 12,500 years.

The creatures, whose shells can survive many thousands of years, demand particular conditions for life so their presence or absence in the layers of sediment can give accurate data on climate change. But Horne found something else was at work when their numbers took a dramatic dive. He examined the pollen in the sediment core and went to libraries to study local history documents, where he uncovered the practice of "retting the hemp" at Quidenham mere.

Retting the hemp was the cause of severe environmental change and Horne had found evidence of one of the earliest human-driven extinction events. Extinction is not new, but the scale and speed of the loss now taking place is. Extinctions are up between 1,000 and 100,000 times the natural rate, says Andrew Balmford, a Cambridge University zoologist.

It is calculated that between 1,000 and 10,000 of every million species become extinct each year. The natural background rate for extinction is only between 0.1 and 1 species a year for every million. "Our own welfare as a species is likely to be damaged quite severely. We don't know what we are losing. There are myriads of biologically active compounds there, some of which are very likely to have very important medicinal properties," says Dr Balmford.

Fears of lasting damage or extinction have spawned a powerful conservation movement. Pressure groups - one of the largest of which is the Royal Society for the Protection of Birds,with one million members - have funded practical initiatives to try to save particular species.

But what has been lacking until recently has been the back-up of more widely applicable research science to underpin the conservation movement. For a long time this was an area that university scientists shied away from in this country. The number of university posts dedicated to researching and teaching conservation is small.

Against this background, Cambridge University has launched a campaign to raise Pounds 2 million for a professorship of the conservation of nature, which will be named after its chancellor, Prince Philip, who, with naturalist David Attenborough, has lent his weight to the appeal.

In recent years Cambridge has become the national, and in some cases international, centre of key conservation organisations, among them the World Conservation Monitoring Centre, Birdlife International, the International Whaling Commission, RSPB and Flora and Fauna International. The aim of the new professorship would be to expand the growing links with these organisations.

"You have to make sure you have asked the questions people want answered," says Dr Balmford, one of the country's few lecturers in conservation biology. "And then you have to make sure you get the answers out to those who can best use them. Nowhere else in the world is there such potential for university scientists to work with major conservation bodies." In the past year a Cambridge Conservation Forum has been established to develop these new links.

The RSPB has recently transferred one of its scientists, Rhys Green, to work in the university zoology department, in a move to marry the practical and broader intellectual aspects of the conservation quest. Dr Green, a research zoologist who helped the RSPB to protect the corncrake, one of our most threatened birds, by researching ways to reduce losses of its nests, has already demonstrated the value of the access to university facilities.

Examining thrushes' eggs in the university's zoology museum from as far back as 1850, he has found evidence of thinning of the eggshells produced by all four British species of thrush. In the case of the blackbird, shells have become 10 per cent thinner. "This could be a symptom of a wider problem. Other species might be even more affected," he speculates.

The last occasion on which such eggshell thinning was detected involved endangered birds of prey. It was caused by the pesticide DDT, and the discovery led to the control of its use, avoiding a further extinction crisis. Birds need a high boost of dietary calcium when they are making shells, and Dr Green is investigating their ability to find it in sources such as snail shells or the soil. To date he has not found any evidence that acid rain is leading to thinning but has not ruled it out. "It is still a whodunnit," he says.

Conservation excites passion, much of it from people who care greatly about the animals and plants involved. It is reckoned that about 1.5 million people support conservation bodies in this country. The Cambridge initiative comes as leading biologists have realised that man's impact is causing an extinction spasm not seen since the wipe-out of the dinosaurs. As growing numbers of scientists turn their attention to conservation, the field is acquiring a new intellectual rigour.

Dr Balmford's research looks globally at ways to assess as quickly and economically as possible which areas should become nature reserves. After that the challenge will be to find ways to modify human lifestyles to limit the damage in the wider landscape beyond reserves.

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