Low-flying helicopters are disturbing wild birds at two RSPB nature reserves in Cornwall, the charity has said.
Visitors to Hayle Estuary and Marazion Marsh are being asked to record details of each incident so the charity can address the issue.
David Flumm, from the RSPB, said some birds had not returned after helicopters had passed over.
The charity hopes the information collected will allow it to approach those causing the disturbance.
Mr Flumm said: "It's been an issue for quite a long time and we've had quite a few complaints from local people and birdwatchers."
During the winter months the birds will be using up valuable energy flying off rather than feeding, he added.
Marazion Marsh is Cornwall's largest freshwater reedbed and is important for warblers and waterfowl.
As regular CFZ-watchers will know, for some time Corinna has been doing a column for Animals & Men and a regular segment on On The Track... particularly about out-of-place birds and rare vagrants. There seem to be more and more bird stories from all over the world hitting the news these days so, to make room for them all - and to give them all equal and worthy coverage - she has set up this new blog to cover all things feathery and Fortean.