Last year marsh harrier, kestrel and wagtail nests were raided along the river between Sculthorpe and Guist.

Eastern Daily Press: The marsh harrier's nest targeted by egg thieves, May 10, 2015.The marsh harrier's nest targeted by egg thieves, May 10, 2015. (Image: Archant)

Patrols will be carried out to protect the nests of rare birds from egg thieves.

Last year marsh harrier, kestrel and wagtail nests were raided along the Wensum Valley near Fakenham. Despite police appeals and a £7,000 reward, the thief or thieves were never caught.

Now conservation group the Hawk and Owl Trust has appointed a warden who will patrol reedbeds along the river at Guist and other locations where rare birds breed.

Nigel Middleton, the group's conservation officer, said: 'We've agreed with the Guist Common trustees, who are the owners of the land, to take him on as the official warden of the site.

'There will be signs going up warning that there are Schedule One breeding birds there.'

Norfolk's river valleys and coastal wetlands are a stronghold of the marsh harrier.

Experts say the UK hosts around 350 breeding pairs of the birds of prey, which were once threatened with extinction.

Harriers will soon begin to pair up and perform their acrobatic aerial courtship, before choosing their nesting sites.

Birds circle each other high above the ground and throw each other scraps of food during their spectacular sky dances.

Tagging experiments have shown that birds fledged in Norfolk travel as far afield as Portugal and Belgium, before returning to the county to breed.

Police urge the public to report any unusual activity around nesting sites during the breeding season.