Only breeding golden eagles produce long-awaited egg

England's only pair of breeding golden eagles are incubating at least one egg at their Lake District eyrie after four years in which the female has not laid any.

The pair were prolific breeders in the late Eighties at the Haweswater reservoir site where they were first noticed in 1969, but experts had feared for years that their breeding days were over. Normal laying time is late March, and the female is now broody and largely confined to the nest, bedding down deep inside - clear signs that an egg is beginning its 40-day incubation. Most pairs lay two eggs at a time.

Mike Everett of the Royal Society for the Protection of Birds (RSPB) said yesterday: "This is always the most crucial and dangerous part. Once the eggs hatch and the young get to a fortnight old you are almost home and dry with golden eagles. There's a long record of nil return on this nest so we are anxious something should hatch."

Of the United Kingdom's 450 pairs of golden eagles, these are the only ones known to nest outside Scotland. They have produced 18 young in their 31 years in the Lakes, although two-thirds never make it to adulthood. The female bird is spending most time on the nest; a young bird will be seen in August, if one does emerge from the off-white egg with blood-red markings.

Bill Kenmir, the RSPB's Haweswater warden, said the news of the incubation had "delighted" the staff. "Last year [the birds] did not nest at all and then, lo and behold, we have an egg in time for Easter," he said.