A marsh harrier with its device. Picture: Eastern Daily Press

The Hawk and Owl Trust is to track young birds reared in Norfolk once they leave their nests to find out more about their distribution and survival.

At about one month old while still in the nest, they are fitted with a tiny transmitter on a lightweight harness.

For about a year ornithologists will be able to find them in a 20-mile radius.

The trust is working with English Nature on the project, called Operation Circus, from the scientific name for harriers, Circus.

We hope not only to discover how far they spread but also which habitats are most important to young harriers at a crucial time when they are learning to hunt Dr Roger Clarke

East Anglia is the stronghold for the marsh harrier. In 1971, numbers had declined to just one pair.

Now there are some 200 pairs mostly nesting in reed beds on nature reserves or specially protected areas.

Dr Roger Clarke, scientific adviser for the Hawk and Owl Trust, said: "We hope not only to discover how far they spread but also which habitats are most important to young harriers at a crucial time when they are learning to hunt."

Nigel Middleton, the Hawk and Owl Trust's conservation officer for East Anglia, said: "Another benefit of the project could be to help protect these birds from direct persecution."