Chicks of the great bustard, which was wiped out in Britain in the 19th Century, are on their way back to Wiltshire.
The bird has not been seen in Britain since 1832
The birds are travelling from Moscow and are expected to arrive in the county this week.
Eggs were collected in Russia from nests threatened with destruction.
Forty chicks of around one or two weeks old will be taken to Salisbury Plain where they will be reared and then released without having seen a human.
Efforts to re-introduce what is the world's heaviest flying bird, nearly 175 years after it died out in Britain, is the aim of the British Great Bustard Group.
Conservationists have flown to the Saratov region of Russia to find chicks to bring back.
Farming and hunting killed British Bustards in 1830s
They stand to the height of an adult Roe Deer
They can be more than a metre long and upwards of 15kg
About 40,000 Bustards are in Spain, Portugal, central Europe, Russia and central Asia
Their alarm call is a short, nasal sound similar to a bark
It is one of the few countries in which the great bustard is known to still roam in the wild.
The chicks' nests are threatened with destruction in Russia so British authorities have importation licences.
The great bustard was hunted to extinction in Britain in the 1830s, partly because its succulent and delicious meat was so sought after by the nation's chefs.
The Great Bustard Group has said the bird is "the missing crown of the biodiversity and natural heritage of England".
Founder and chairman of the group, former Wiltshire Police wildlife liaison officer David Waters, said there could be teething problems for the re-introduction of the birds in the UK.
He said: "The adults can live for up to 20-25 years, but the survival rate for great bustard chicks in the wild is not great - 75% of them will die in the first year.
"They do have a capacity for injuring themselves and the simple fact of the great outdoors is that there are a lot of things that eat each other."