Swan song for beautiful Bewick's? Not if this woman can help it.

The Bewick's swan, one of britain's most beautiful winter visitors, is under threat. Its numbers have dropped by half in a decade, and no one knows why.

It breeds on the north russian tundra but when the harsh siberian winters close in, the birds migrate south, to avoid the plummeting temperatures.

Researchers in Exeter are behind a project to try and investigate.

To find out why their numbers appear to be in decline, a conservationist from Slimbridge Wildfowl and Wetlands trust in Gloucestershire, is going to fly with them.

Sacha Dench will be using a paramotor to fly from arctic Siberia following the birds 4,500 miles as they migrate south across europe and into the UK.

To train for the project, which is launched today and gets underway in september, Sacha has been out to Sweden to get used to flying in freezing temperatures.

Sacha will follow the migrating swans at a discrete distance, keeping up with them using satellite tracking. Some of the birds have been fitted with electronic tags. but there will be days when the weather closes in and it is impossible to fly.

There are other dangers too. Though she will have a back up team the first few hundred miles will be alone, as the landscape will be impassable. If she has to make an emergency landing, she could be on her own.

Sacha's trip will be long, arduous, but could yield valuable scientific evidence about why Bewick's swan numbers are in decline.