It has been a fine week for David Walters. After 10 years' work, and the investment of more than £100,000 of his own cash, his great bustard project reaped rich dividends last Sunday. Two of the birds that he had reintroduced from Russia to Britain were found to have hatched chicks. "They are the first British bustards to be born in 177 years," he announced proudly last week.
The bustard project is remarkable for the efforts of Walters, a former Wiltshire policeman. It is also striking because it is one of several recent species reintroductions that have been achieved by ecologists trying to reinvigorate the nation's biodiversity. Other successes include the red kite, the white-tailed eagle and the beaver.
Now follow-up plans are being prepared for the short-haired bumblebee, the hen harrier and the corncrake. However, none is likely to match Walter's bustard reintroductions on Salisbury Plain for the commitment of its organiser.
"People spend huge sums of money on holidays to the Galápagos or Tanzania to see exotic animals," said Walters. "But a great bustard, apart from having a smashing name, is an extraordinary bird. It has an 8ft wingspan and looks like a crane on steroids. And when the male displays, it just about turns itself inside out. As a flagship for UK wildlife reintroductions it is simply unbeatable. I had to bring it back to Britain."
The great bustard was wiped out by the spread of intensive farming and the attentions of bird-egg collectors in the early 19th century. The red kite and white-tailed eagle followed a little later, finished off by hill farmers and gamekeepers who thought these predators were killing their animals. In fact, they live more on carrion than on catching their own prey. "However, we have a more enlightened attitude today, so we think it is safe to bring them back," said Graham Madge of the Royal Society for the Protection of Birds.
The ultimate aim is to return the British countryside to a richer and more diverse state. But just as it is important to reintroduce lost species, it is also vital to control foreign invaders endangering existing indigenous plants and animals, say ecologists. A key example is provided by the grey squirrel. An American import, it is now driving our native red squirrel to extinction. Last week, the Country Land and Business Association called for a government cull because, it said, grey squirrels were destroying our broad-leaved woods by damaging the bark of maturing trees.
Then there is the Japanese knotweed, which costs the nation tens of millions of pounds a year to clear up. "It was introduced by Victorians to give colour to their gardens, but has gone from being a prizewinner to a pariah," said Dr Richard Shaw, a principal investigator at the Centre for Agricultural Bioscience International. "It is the biological equivalent of concrete."
Knotweed forms thick, suffocating layers while similar plant pests - such as the Himalayan balsam and floating pennywort - are also having a disastrous impact, Shaw said. Pennywort covers ponds, streams and rivers with the result that they lose their oxygen and fish can no longer breathe. It strangles native plants, but provides no sustenance for our insects. Their numbers plunge, as do populations of birds that feed off them.
These invaders are having the same impact on wildlife as gamekeepers had on the red kite and white-tailed eagle in the 19th century, in other words. Hence the plan by Defra and other government agencies to wage war on the Japanese knotweed - by introducing the plant's native predator, the jumping plant louse, to Britain. The louse lays eggs on the plant and the hatched larvae suck out its sap.
"We tested more than 180 native species of insects found on knotweed in Japan and picked the jumping plant louse because it was the only one that is specific to the Japanese knotweed," said Shaw. "That means it will not spread to other plant species."
Nevertheless, the move does mean that another non-native species could soon be introduced to Britain, albeit one that has been carefully studied and tested. This raises key questions about what kind of wildlife we want for Britain and the measures we are prepared to take to ensure that it is kept healthy and diverse.
Why should we reintroduce beavers or red kites or import insects to kill off invaders such as Japanese knotweed? The answer is simple, according to Andrew Wood, of Natural England, the government's environment advisers. "The more diversity, the healthier the environment," he said.
"If you think about the plants we exploit for food, the fewer we have, the more we are exposed to the dangers of crop disease, for example. Then there is the issue of the relationships between species. You need top predators such as the white-tailed eagle to help keep down populations of small mammals, or red kites to clean up carrion. And then there is the role of an animal in a specific area - such as the beaver. They keep woods well channelled with waterways that act as natural purification systems. So, yes, we have a great deal to gain from reintroductions and by keeping our wildlife as diverse as possible."
