The children found him in July, while gathering eiderdown in Iceland's long summer days - the body of Oscar the goose, dead on the island of Hjorsey, with yellow rings on his legs and a satellite transmitter on his neck.

Migrating geese die all the time, but Oscar was no ordinary bird. Science and showmanship have turned the great annual migration of Oscar and five other light-bellied brent geese into a combination of birdwatching, transatlantic race, and Big Brother style elimination game show.

Thousands of people have logged on to the website of Britain's Wildfowl & Wetlands Trust to follow the satellite-tracked progress of the geese - Major Ruttledge, Austin, Hugh, Kerry, Arnthor, as well as Oscar - on their 9,000 mile journey from Ireland to Arctic Canada and back.

A handful of enthusiasts have paid £75 to "adopt" one of the geese. In return, they have been getting regular text messages on their mobile phones updating them on the birds' progress. There are even unconfirmed rumours that an internet gambling site is taking bets on which of the geese makes it back to Ireland first.

That is, if any of them do. The geese are on their homeward journey, but two have already been knocked out in the harshest fashion. Oscar was the first to go. He never made it beyond Iceland, the birds' first staging point on their northward journey.

"It was strange. He started to move with the other geese, and moved within Iceland. Then we found the transmitter was still transmitting, but the bird wasn't moving - when it was getting to the time he should have gone to Canada," said James Robinson, the trust's research officer.

The trust speculates that Oscar was an older bird, who found the first leg of the journey too exhausting, or that he may have fallen victim to a predator such as a gyrfalcon.

Mystery surrounds the disappearance of the second goose to drop out, Arnthor. He survived the ocean flights from Ireland to Iceland. He also managed the trip from Iceland to Greenland - where the geese fly for 12 hours solid, then drop down to the cold, stormy waters to rest - and the climb to 8,000ft to cross the vast Greenland icecap.

Then, somewhere on Disko Island, on the west coast of Greenland, his transmitter went dead. Dr Robinson said the transmitter may have stopped working, but the most likely cause was that Arnthor was shot by a subsistence hunter for the pot, in defiance of laws protecting the species.

The other four birds made it to Canada, where they fed and and then bred. The tracking shows they have now looped back for home.

The exercise has a serious scientific purpose. Information on the migrations will give weight to setting up international agreements to protect the habitats that are important to this population each step of the way. To date, there has been little study of the migrations of this species of goose, whose journey is the longest of any such bird.

In the world, there are about 20,000 light-bellied brent geese. Stocky and with dark plumage, they eat enough to put on about a third again of their body weight to help them migrate north in spring and south in late summer. Almost all the birds who survive winter in Ireland, from the end of August. By late September, most of the birds are thronging Strangford Lough, near Belfast. Some of them stay the winter in other parts of western Europe.

"We learned much about the route when the geese undertook their spring migration," said Dr Robinson.

But there have been surprises about the latest migrations. This time the birds failed to stick together, dispersing to various Canadian islands.

The four remaining among the geese are still available for people to "adopt" at www.wwt.org.uk/brent.