Springwatch presenters were left confused by activity at a shelduck burrow which prompted them to look into further.

The series aired its sixth episode on BBC Two on Wednesday, June 2 live from Wild Ken Hill in west Norfolk with presenters Chris Packham and Michaela Strachan, with fellow hosts Iolo Williams in Scotland and Gillian Burke in Northern Ireland.

Eastern Daily Press: Springwatch presenters Chris Packham and Michaela Strachan at Heacham Bottom Farm.Springwatch presenters Chris Packham and Michaela Strachan at Heacham Bottom Farm. (Image: Archant 2021)

Ms Strachan told viewers on Wednesday night's programme that they had a mystery on their hands with the shelduck at the Norfolk site, showing footage of a burrow at the bottom of a tree which they are nesting in.

She said one female comes out the burrow and flies off, which was not unusual, but then 44 minutes later another female comes out the burrow.

She added: "Between the two there wasn't anything that went back in.

"Later on one of them comes back in, 20 minutes later another female waddles back in.

"Now this kept going and we thought 'this is curious, what's going on here?"

The presenters said they wondered if there was another entrance but they could not find one, confirming that the birds were both female.

Ms Strachan said: "So what on earth is going on there? Could it be that in that burrow there are two nests or that they're both sharing the same nest?"

A specialist was called in to put an endoscope into the burrow revealing a nest.

Eastern Daily Press: The wonders of Norfolk's wildlife will be broadcast to millions from Wild Ken Hill, when Springwatch 2021 gets under wayThe wonders of Norfolk's wildlife will be broadcast to millions from Wild Ken Hill, when Springwatch 2021 gets under way (Image: Archant 2021)

Mr Packham said: "I don't think there's two females incubating the same clutch of eggs and the same nest at the same time.

"I think there must be another chamber with another nest in it."

He said when the nests hatch they will be able to get an answer as it unlikely they will hatch at the same time, with Ms Strachan branding it a "mystery unsolved" at the moment.

Later in the programme, the work that goes into managing a 300-acre marsh was revealed.

Conservation manager Lloyd Park told Ms Strachan Wild Ken Hill had undertaken a project to redevelop the area in order to hold water back and create marshes for birds such as avocets.