A webcam trained on their man-made nest was so popular the birds will find two cameras and a microphone there when, it is hoped, they return next year.
He said the key to the fish-eating birds' popularity was the live feed from the webcam, revealing life inside the nest, relayed onto a large plasma screen at the visitor centre.
"A lot of local people came in every day to keep up with the soap opera. That's how we pulled in 75,000 people - it was something like a soap story," said Mr Evans.
"It was great watching the live net cam images, but it was a bit like watching a natural history programme with the sound down. The microphone will just give that extra dimension."
The plan to increase camera footage from the nest is to be explained at a meeting of around three dozen organisations which help fund the RSPB project at Beddgelert in Gwynedd, on Thursday.
Mr Evans said the parent birds, currently wintering in west Africa, are expected back in March 2006, and it was hoped they would return to the nest for the third year running.
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