Sacha Dench will use a motorised paraglider to track the Bewick’s swan on its journey from Siberia and discover why numbers are falling

In a few days, conservationist Sacha Dench will take to the air in the most unusual company. She will launch herself from the tundra of Siberia in a motorised paraglider and, when airborne, she will follow the thousands of Bewick’s swans that will have begun their annual migration from the Arctic to their wintering grounds in western Europe.

The 4,600-mile trip will take several weeks to complete. Dench will either camp in the open or seek shelter with local people, including Nenets, nomadic reindeer hunters.

Then she will return to Britain with information that she hopes will help to solve an ornithological mystery: the relentless decline in the number of Bewick’s swans over the past 20 years. In 1995, there were around 29,000 Bewick’s in Europe; by 2010, the figure had dropped to 18,100 and the numbers have continued to decline.

“The problem is that we do not know why,” Dench told the Observer. “I hope to provide the answer.”

Several factors may be involved in the Bewick’s decline, say experts. One is illegal shooting. More than a third of the Bewick’s examined by staff of the Wildfowl and Wetlands Trust (WWT) have been found to have shotgun pellet wounds. They survived but thousands of others may have been killed by Russian and eastern European hunters as the birds have flown over their countries.

“However, there may be other factors,” said Dench. “The disappearance of wetlands, which the swans like to land on; predation from other animals; the proliferation of power lines, which the swans strike in mid-flight; and climate change, which is altering the vegetation on which the swans depend – all of these may be involved. I hope to find out the culprits.”

Facebook Twitter Pinterest Sacha Dench in training in Devon and Cornwall for her Flight of the Swans, following Bewick’s swans migrating from the Arctic Photograph: Ben Cherry/WWT

The Bewick’s swan is seen as a key species to study because the birds particularly interested Sir Peter Scott when he set up the WWT at Slimbridge in Gloucestershire after the second world war. Scott realised it was possible to identify individual animals from their bill markings.

“We have named about 10,000 over the years,” said Dench. “We know a lot about the lives and characters of Bewick’s, so in that way they are very special.”

In 2012, as the numbers of Bewick’s swans reached an alarmingly low level, an international action plan was agreed by countries that lie beneath the birds’ migration path. Dench’s expedition – known as the Flight of the Swans – is the culmination of that effort.

She will act as a “human swan”, tracking Bewick’s as they leave the Arctic, where they have been feeding over summer, and head west and south – through Finland, Poland and Germany – to their wintering grounds in Britain and other parts of western Europe.

And she will do this in her motorised paraglider – a flimsy contraption consisting of a seat, a parasail, an engine and little else. Exposed to the Arctic elements, and travelling at around 35mph, Dench hopes she will be able to track Bewick’s for about six weeks as they flee the bitter cold that settles over northern Europe in the autumn.

Her flight, which has been backed by Dame Judi Dench (a distant relative), Sir Ranulph Fiennes and Sir David Attenborough, will be arduous, to say the least. Dench will have to spend many hours every day in her tiny craft, open to the elements, while relying on the hospitality of Nenets and other locals while on the ground. She will also have to sleep in the open on some occasions.

Her flying skills will be critical to the mission’s success. Yet the 41-year-old conservationists admits that she only took up paragliding a few years ago because she had developed a fear – of flying. “I had been in a very small plane that got caught in a thunderstorm in Panama and we were thrown about in terrible turbulence. I decided I had to get my nerve back and so I took up paragliding.”

Dench has since amassed years of paragliding experience and has also been put through tundra survival courses, practised landing in water and rehearsed “all the things that could possibly go wrong” with her craft.

Dench will fly to Moscow on Sunday before heading to Siberia with the aim of beginning her voyage with the Bewick’s on 15 September. It is around this date that the swans respond to the increasingly cold temperatures in the Arctic and fly, in their thousands, to the west and south. She expects to complete her journey in late October.

She will have one comfort, however. Dench’s parents have both prepared playlists for her to listen to when aloft. “My mother has already given me her list,” said Dench. “It is a very broad selection and has tracks from Edith Piaf and Jacques Brel to Tina Turner and Dire Straits.

“My father has not yet sent me his, though to judge from the way he has been quietly chortling about it, I suspect there is going to be the odd dig about my flight. I wouldn’t be surprised if I end up listening to tracks like If You Want To Be a Bird or Ride a White Swan by T Rex as I am flying over the tundra.”