The first osprey to arrive this year was spotted on 21 March, but poor weather and the presence of other predators meant only six chicks survived.
That followed a tough year in 2024.
“The really vulnerable time is when eggs hatch and unfortunately we had quite cold, wet weather this year so the numbers have been lower than expected,” Mr Dearnley said.
“The first year of migration is always really tough anyway because a bird is learning it for the first time.”
The Osprey Watch scheme – a partnership between Forestry England and other organisations including Northumberland Wildlife Trust – allows the birds to be viewed around the clock on high-definition cameras.
There is also a dedicated viewing spot at one of the site’s visitor centres while osprey-watching ferry tours run on the reservoir.
“They have dramatic habitat,” Mr Dearnley said of the birds. “They dive for fish and are very visible.
“We can explain more about all the wildlife in our forest by using them as a focal point. It’s a great species to engage with.”