There has been a "noticeable change" in the feeding behaviour of the birds, suggesting they now had at least one chick.

The male osprey has so far raised 13 chicks with different females.

'Good sign'

David Hirst, from the RSPB, said: "We are basing our detective work on the behaviour of the birds.

"Everything now suggests that there is at least one chick in the nest. The female bird is now sitting really tightly on the nest and the male bird is bringing many more fish into the nest.

"Until last weekend he was bringing three or four fish in a day. Now he is bringing about four fish in every hour.

"That is a really good sign that there are some youngsters in the nest."

The nest site is monitored by the Lake District Ospreys Project, which is a partnership between the Forestry Commission and the Royal Society for the Protection of Birds with the support of the Lake District National Park Authority.

It is estimated that the birds boost the local economy by up to £2m every year.