More than 77,000 people have visited Cumbria this year to see nesting ospreys, officials have said.
The osprey chicks have been ringed
But the Royal Society for Protection of Birds (RSPB) says time is running out for those planning a trek to Bassenthwaite in the Lake District.
Two adults and two chicks have attracted record crowds to a special viewing centre.
But the RSPB says the birds are expected to begin their migratory flight to Africa shortly.
The adult pair of ospreys first nested at Bassenthwaite Lake in 2001. Since they arrived back in Cumbria in April they have become one of the area's main tourist draws.
Latest figures from officials at the Lake District Osprey Project show that so far this year 77,500 have seen the four birds.
Special cameras have beamed continuous live footage from the ospreys' tree-top nest overlooking Bassenthwaite Lake to a visitor centre.
An RSPB spokesman said: "All four ospreys can still be seen in the Bassenthwaite area, but the female osprey is expected to head south any day now.
"The two chicks have now flown the nest and are growing up fast in preparation for their first flight to West Africa, where they will spend the winter."
Graeme Prest, of the Lake District Osprey Project, said: "This has been the most exciting osprey season in the Lake District so far, with more ups and downs and twists and turns than a rollercoaster."